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#460000 - 10/22/12 12:46 pm Re: Restoring a Rotating Armature Magneto ***** [Re: Magnetoman]  
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Thankyou for posting this detail on the mechanical side of magneto restoration.

In my early attempts at classic racing I ruined two sets of pistons before I realised the asymmetry of my ignition timing due to poor alignment of the armature.

While checking to this level of detail may seem over the top for everyday use it is exactly this sort of accuracy that makes the fastest bikes go fast!! (and reliable!!)

If you get every setting - ignition, cams and valve timing, carbs exactly right with a blue printed motor you will gain at least 5 bhp on a 500 cc bike. 8 bhp on a 750.

John

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#460007 - 10/22/12 1:36 pm Re: Restoring a Rotating Armature Magneto [Re: Ken Tee, R.I.P.]  
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Originally Posted By: Ken Tee
Why would the rubbing block wander in and out? (apart of course from the effect of the cam.
Thanks for noticing this. I'm editing with Iphone so easiest to just delete that clause, which I just did.

#460013 - 10/22/12 2:43 pm Re: Restoring a Rotating Armature Magneto [Re: johnm]  
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Originally Posted By: johnm
While checking to this level of detail may seem over the top for everyday use it is exactly this sort of accuracy that makes the fastest bikes go fast!! (and reliable!!)
Thanks very much for your note. It's nice to know the information is being read and appreciated. While h.p. wasn't a concern for this particular restoration, it comes as a free added bonus with reliability and smooth running.

An impression of "over-the-topness" might come from my description of this restoration being spread out over four months by the time I'm done. However, although I didn't keep track of the time spent actually working on the magneto, what is taking four months to describe probably added up to the equivalent of about two days of work on it. The magneto was actually in my hands for 29 days, during which time I made two trips across the country, plus worked at my normal job.

If the level of attention I used on this magneto does strike some people as over the top, all I can say is, it's not. It certainly is possible to get away with a much worse restoration than the one I'm documenting here and still have the magneto function, just as it is possible to do a poor rebuild of an engine using improper clearances and ill-fitting aftermarket parts and still have the engine run. Also, while I am equipped with some over the top instruments, e.g. the Talyrond of my most recent installment, in all such cases there are "normal" pieces of equipment that could have been used instead (a mill's rotary table instead of the Talyrond). Some tools are specialized (e.g. a Merc-o-tronic tester), but specialized tools also are needed to rebuild an engine (e.g. a cam pinion extractor). The point is, the tools I used would be needed by anyone who is capable of doing magneto repairs properly, and their work would be done to the level of detail I'm describing.

Last edited by Magnetoman; 10/22/12 6:14 pm. Reason: fixed typo
#460165 - 10/23/12 7:22 am Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Yes it is a game to catch young and not so young players.

I measured 8 degree difference on an old Lucas K2F mag due to bad armature alignment. I kept trying to fix it by grinding the cam ring and ruined a second set of pistons before I finally realised. I was being a bit stupid really and should have figured it out earlier if I had not been diverted by other issues.

On my race bike I set ignition to within 0.5 degree both sides and have experimented with the dyno to get the best setting for petrol and methanol.

Many magneto servicing places address the electrical issues but not the mechanical issues

Last edited by johnm; 10/23/12 7:28 am.
#460272 - 10/23/12 8:20 pm Re: Restoring a Rotating Armature Magneto [Re: johnm]  
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Originally Posted By: johnm
I measured 8 degree difference on an old Lucas K2F mag due to bad armature alignment... Many magneto servicing places address the electrical issues but not the mechanical issues
This is a very important point, and you clearly understand the issue.

I didn't measure the slope of the ramps on the Bosch's cam, but on a Lucas K2F it is ~2.4-deg. of engine rotation per 0.002" of lift (1.2-deg. of cam rotation). That means that even if the cam is made perfectly, and you set the points to open on one cylinder precisely where you want them to, but if the cam is held in the housing such that its centerline is offset from the centerline of the armature by only 0.002", the other cylinder will fire 2.4-deg. too soon or too late.

Magnetos are electro-mechanical devices, so even if the electrics are in perfect condition, that only takes care of the 'electro-' half of the problem. As a preview of a future installment, one of the upcoming tests will be of the restored magneto run on my modified distributor tester at 1250 rpm (2500 rpm engine) to determine precisely where both cylinders fire during actual operation, and to see how much variation there might be during operation (due to, say, sloppy tolerances).

#460362 - 10/24/12 10:23 am Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Can I ask your opinion about using a strobe light to check the accuracy of timing on a mag ? At least one manufacturer's website does not recomend it but they do not explain why.

I have used my strobe powered by a separate bike battery to check the magneto timing on both cylinders for years. I have scribed a line on the belt drive plate and marked up the cover in degrees. I find this is a very quick way to check timing after and during a meeting.

I use a vernier on the sprocket to adjust the timing on my Norton twin but confess that I have also used points gap to swap the bike quickly from petrol to methanol timing in the middle of the meeting when trying to run one bike in two classes.

If you set the timing at one extreme of recomended points gap range for petrol you can then get the 3.5 degree extra advance necessary for my bike to go to methanol. I can then check very quickly with the strobe that I have got it right. I know this means the flux peak (not the right words but you know what I mean) might not be optimal but the best I can do in a few minutes between races. This is on a Fairbanks Morse/Hunt/Morris type rotating magnet mag.

This is all usually done in a 20 minute organised panic of three guys swapping carbs, front brakes and ignition timing to move up from Clubmans to Open class. It has proved successful with a couple of seconds in the NZ Classic Senior TT on a upgraded Clubmans machine!

Any other suggestions gratefully considered.

Last edited by johnm; 10/24/12 10:38 am.
#460418 - 10/24/12 6:22 pm Re: Restoring a Rotating Armature Magneto [Re: johnm]  
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Originally Posted By: johnm
Can I ask your opinion about using a strobe light to check the accuracy of timing on a mag ? At least one manufacturer's website does not recomend it but they do not explain why.
There is no reason whatever not to use a timing light with a magneto, although there are two significant practical issues that get in the way: 1) an appropriate, accurately located, timing mark, and 2) adjusting the timing.

1) Later non-magneto bikes had timing marks on the rotor, and even later ones still provided an access plate that didn't necessitate removing the entire primary case. The problem on an earlier bike is to find a component on which to make suitable marks in a location where oil won't spew out when it is uncovered. It sounds like you've found a solution to this on your racing bike.

2) Later bikes swapped the positions of the cam and the points, rotating the former rather than the latter. This makes it much easier to provide an adjustment mechanism to move the points relative to the cam. Again, you've solved this problem with a vernier on the magneto sprocket. However, it does require removing a cover to get access to that sprocket.

I've never done this myself, but it wouldn't be too hard to design a screw mechanism on the body of the mag that would basically replace the timing cable (I realize yours is likely locked at full advance, so you don't have a cable). You would still use the vernier to get as close as you could to the proper timing. But, during a race meeting if you found with your strobe that the timing was off by a fairly small amount, tweaking the cam angle slightly with the screw mechanism (securely located as part of the body of the mag) could quickly dial it in to being spot on.

#460999 - 10/28/12 4:09 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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REASSEMBLY, REMAGNETIZING, AND EXTENDED STRESS TESTS:

Finally, this Bosch ZEV magneto is ready to go back together. After cleaning off the unknown grease that the rebuilder had used on the bearings, I packed them with Sta-Lube high temperature disc brake bearing grease, applied a small amount of Lubricam to the cam and its pivot, and reassembled the magneto. I also put a yellow tag with a note on one of the oil cups telling my friend not to use oil, since it would only wash the grease away.

End Float

BTH and Lucas armatures have shims for both the armature shaft and for the housing to adjust end float, so just the fact these shims exist indicates it is something that needs to be checked. Especially with magnetos rebuilt by someone else it almost always needs to be adjusted. Since this magneto has a new bearings it means both races were removed and reinstalled by the previous restorer, and the position of the races determines the end float. Anyway, given how many problems I had found with this magneto, checking the end float was especially important. Inserting 0.005" shim stock between the end cap and the main housing and then measuring the end float of the armature let me determine that the end float would be 0.000" with no shim at all. I don't know if Bosch ever published specifications for the end float for this magneto but, even if they did, I don't have them. However, the only reason to use shims to get a positive end float would be if the thermal expansion of the armature was significantly larger than that of the housing, resulting in undue pressure on the bearings at operating temperature. Several years ago I made careful measurement of the thermal expansion of a Lucas armature and housing constructed of similar materials as used by this Bosch. Those measurements, plus the fact Lucas called for zero end float (0.005" max.) for their magnetos, makes me confident in using zero for this Bosch ZEV.

Contact Spring Pressure

An important measurement is of the spring pressure on the contacts. If it is too small the points will float at high rpm, and if it is too large the rubbing block will wear too rapidly. Because removing the cam leaves the rubbing block exposed on this magneto it is particularly easy to measure, as is shown in the next photograph taken using my ZE1.



Lacking specifications for this pressure from Bosch required deciding on a reasonable value for comparison. Literature from various magneto manufacturers has at the low end of the recommended range for tungsten points 10-18 oz, and at the high end 15-30 oz. Consistent with this, I measured my Vincent's Lucas KVF to be 24 oz, although its spring needs to keep the rubbing block in contact at nearly twice the rpm as does the 1923 Harley-Davidson's magneto. Complicating this further is that when I removed the ZEV's moving point arm from the assembly I found its balance point was slightly towards the contact end. Because of this, centripetal force will tend to open the points against the action of the spring, and this force increases as the square of the rpm.

With the above as background, I measured both the Bosch ZEV and the ZE1 at 13-14 oz. Although it is encouraging that they are the same, unfortunately, it may only mean their springs have weakened with age by the same amount. However, since 14 oz. is a reasonable value, although toward the low end, I decided to proceed with testing. I made a note that cannibalizing the spring from my ZE1 to use to double the pressure on the ZEV is an option, depending on what I find from my dynamic tests of the magneto (although this would move the pressure from near the low end of recommendations to near the high end).

Magnetizing

It's impossible to properly restore a magneto without being able to remagnetize it, so several years ago I made an appropriate electromagnet. I based its design on requirements given in the 1953 Lucas Workshop Instructions booklet Remagnetisation of Magnetos, after also checking specifications for magnetizing Alnico in several texts. The Lucas booklet calls for an electromagnet with a core winding value of 65,000-70,000 A-turns in order to magnetize their post-WWII Alnico-based magnetos.

Incorporating construction principles detailed in Laboratory Magnets by D.J. Kroon (Philips Technical Library, 1968), the electromagnet I built weighs several hundred pounds and consists of ~4500 turns of 14 AWG wire of total resistance 12.9 Ohms wound on a yoke made of Armco magnet iron. Since its inductance stores a serious amount of energy at full current, and such a DC current is difficult to interrupt without arcing, I use a 20 Amp Variac to ramp the current up and back down over a few seconds. Also, having an electromagnet whose field can be varied continuously, rather than only operate on/off, has other advantages for experimentation on magnetos. In any case, applying the full 240 V of rectified AC from the wall results in 18.6 Amps, and therefore 83,721 A-turns, which is comfortably above the values Lucas recommended for remagnetizing their Alnico-based magnetos. I use a clamp-on ammeter during operation to verify the applied current, and also used this ammeter along with a Bell digital gaussmeter to determine the full field vs. current curve of the electromagnet.

Interchangeable Armco iron pole pieces have faces that are shaped to closely conform to a variety of Lucas and BTH rotating armature and rotating magnet magnetos to minimize flux leakage. Further, I have pole pieces to remagnetize Lucas rotors from later motorcycles. Actually, the operating fundamentals of magnetos don't leave a lot of room for unique designs, so these pole pieces also work on Fairbanks-Morse (and A.R.D., Joe Hunt, and Morris), Splitdorf, Wico, etc. If I ever needed, I also have blanks to machine into whatever shape is required. However, simple flat pole pieces are all that are needed for this Bosch magneto.

Because the magnets on the Bosch ZEV are exposed they can be placed in direct contact with the pole pieces, so the amount of flux lost to "leakage" is significantly less than with a post-WWII magneto where the Alnico is encased beneath a shell of aluminum. Even if this were not the case, the ~84,000 A-turns of my electromagnetic is over 2x higher than that needed to fully magnetize the tungsten steel used for the ZEV's magnets (as well as higher than that needed for the later cobalt steel that preceded the Alnicos), so there is no question this electromagnet is able to fully magnetize this magneto. The next photograph shows the magneto ready to be magnetized. I already have attached the aluminum pulley that I normally use to drive magnetos at 2000 rpm on my long-term tester (more about this in the next installment).



For the magnet to be left with the maximum remnance the armature must be oriented correctly when in the electromagnet. However, the precise orientation isn't too critical, so this is easy to do by rotating the armature "backwards" by ~90-deg. from the position where the points are about to open (i.e. turn forward until maximum resistance is felt, then back by ~90-deg.). Although it only requires one cycle up to the full magnetic field to magnetize a magneto, I ran the magnet up a second time for good luck. After magnetizing the Bosch ZEV I attached the two HT cables and found that just a gentle flick of the armature gave an impressive spark.

Note, though, that while it is comforting to see a spark, such a "flick test" is often incorrectly used to claim a magneto is functioning properly. First, if a small gap is used for this test (e.g. the ~0.02" of a spark plug), a much smaller voltage is required to create a spark than will be necessary at the ~150 psi cylinder pressure during actual operation. Second, the instantaneous rpm when the armature is flicked through the position where the points open and the magnetic flux reverses typically is higher than it will experience at tickover speeds, again deceptively making it appear that the magneto is performing better than it actually is. Only a test using an appropriate gap (~0.2") and under steady-state operation can properly determine if the magneto is functioning as it should.

----------- Sidebar About Magneto "Chargers" -----------
Since it seems to be a common misunderstanding by many people who restore magnetos, it is worthwhile explaining why an electromagnet designed for earlier magnetos will not fully magnetize a post-WWII Alnico-based magneto. Just the fact the magnetic energy stored in Alnico is over twice that of the previous generation of Co steel magnets indicates a higher field electromagnet is required. Also, post-WWII magnetos have their Alnico magnets encased within an Al housing so the pole faces of the electromagnet cannot be brought into direct contact with them as they previously could be with the older horseshoe magnets. Because of this, some of the magnetic flux from the electromagnet "leaks" away through the Al housing without reaching the Alnico and as a result an even larger electromagnet is required for these "modern" magnetos than otherwise would be needed.

As an aside, the field produced is determined by the current and number of windings, which in turn determines the wire diameter, operating voltage, and overall size of an electromagnet. Because of this, someone who is familiar with the design of electromagnets can tell just by looking at one if it is capable of magnetizing Alnico. Just as someone who is familiar with engines can tell just by looking at a BSA Bantam and a Vincent Black Shadow that one is capable of 120 mph and one is not.

An electromagnet must be capable of driving the magnet into full saturation in order that it be left with the maximum remnant field once the magneto is removed from the electromagnet. The 2672 Oe of my electromagnet is ~20% more than that needed to fully magnetize a magneto containing anything from the Alnico family (Alnico, Ticonal, Alcomax, etc.), and it is 2.3x more than needed for older steel magnets. Stated differently, the field from an old magnet charger is a factor of ~2x too low for Alnico. This leaves an Alnico-based magneto less than fully magnetized (however, magnetic properties are nonlinear, so the performance is degraded by less than 2x). Although the field from earlier chargers is enough to magnetize an Alnico-based magneto sufficiently to spark an engine when it is kicked over at a higher speed, the magneto will have significantly degraded performance because the Alnico is only partially magnetized. The effects of this will be most pronounced in the form of harder starting and missing under load at low speeds.

Despite these scientific facts, some restorers insist their old chargers work "just fine" with Alnico, and that their customers are happy with the results. If you would accept as "just fine" the performance of your car if returned from servicing with a plug wire disconnected, you can accept the use of an old magneto charger on your post-WWII magneto. Otherwise, not.

Another important point is that a magneto has to be magnetized after it is fully assembled. The negative consequences on performance of magnetizing it with the armature removed (or removing and replacing the armature after magnetizing it) are amply documented in a various authoritative texts on electromagnetic devices. For example, in their chapter 'Magnetising and Timing a Magneto' in 'Automobile Electrical Equipment' (Iliffe, 1958), A.P. Young and L. Griffiths write that if the armature is removed and replaced "The flux density instead of being of the order of 10,000 lines per sq. cm., would be more nearly approximate to 7,000 lines per sq. cm…," i.e. the output of the magneto would be reduced by approximately 30%. In 'Permanent Magnets' (Pitman, 1949), F.G. Spreadbury shows that the output from a magneto with a Ticonol ("Alnico") magnet is reduced by 23% in actual operation if the armature is withdrawn and then replaced after magnetization. Even the Lucas shop manual on 'Remagnetisation of Magnetos' says "... it is necessary to remagnetise them, particularly after an armature or rotor has been removed from a magneto for repair or examination." My own measurements are consistent with the 20-30% reduction documented by these authors.

Despite the information in the previous paragraph, one company offers a service that magnetizes magnetos with the armatures removed from them. Further, they don't merely say that it is "just fine" to do it this way, but actually claim their measurements show it is just as good as magnetizing them when fully assembled. To paraphrase a line from a Marx brothers movie, "Who are you going to believe, this company, or all those lying books?"

Like the use of older magnetizers, people who have their magnetos remagnetized with the armatures outside them are not getting what they pay for. As the references cited above show, these magnetos have 20-30% degraded performance, depending on which member of the Alnico family is inside. By the early 1950s Lucas had used Alnico, Alcomax, Ticonal E, Ticonal G, and Alcomax 2, and my guess is that by the end of the decade they also had used Alcomax 3 and Alcomax 4. Although there is no reasonable way to determine just which member of the Alnico family is inside a given magneto, the B-H loops of all are similar enough that the figure of 20-30%" degradation should cover all possibilities.

Once again paraphrasing Bruce Springsteen's 'Magic', as far as magnetizing a magneto is concerned, "Trust none of what you hear, and less of what is claimed." Only a large, 65,000+ Ampere-turn electromagnet used on a completely assembled post-WWII magneto will fully magnetize it. Further, if you remove the armature for any reason from one of these magnetos (such as to replace a faulty condenser), it will have to be remagnetized after it is reassembled or it will have 20-30% lower output than it should have. It is even worse for a pre-WWII magneto, which won't effectively function at all until it is remagnetized.

A few final comments about the magnets: An often repeated piece of advice when restoring magnetos is to immediately place a steel "keeper" across the poles of the magnet as soon as the armature is removed to keep the magnet from losing its strength. Unfortunately, this advice is wrong. No matter how fast you are, a keeper will do you no good at all because the magnetic domains rearrange themselves nearly instantaneously (less than a millisecond). However, enough strength will be left that the magneto will still spark across a spark plug at atmospheric pressure, so you might think things are fine. They are not. A few other wrong, but harmless, pieces of advice you might run across for achieving full magnetization include charging the magneto 4-5 times (once is enough), holding the electromagnet at full field for a number of seconds (a fraction of a second is plenty), and tapping the magneto with a brass hammer while the field is applied (harmless, but pointless).
----------- End Sidebar About Magneto "Chargers" -----------

Send questions or comments to classic.vehicle.electrics@gmail.com.

#461690 - 11/03/12 9:05 am Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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In his last post, Magnetoman said something very important, albeit in parentheses:
Originally Posted By: Magnetoman
... a magneto needs to be magnetized when fully assembled (or with proper keepers).

The Lucas N1, KN1, K1F, K2F and KVF magnetos and MO1 and MN2 magdynos include internal keepers (the extensions of the pole laminations that extend underneath the armature and almost meet opposite the magnet). That is presumably why Lucas explain in their 1953 workshop instructions specific to these models of magneto that it is not necessary to apply a keeper when removing the armature. Equally, an extra keeper is not required when removing an internal remagnetising core from and inserting the armature into these particular models.

However, some other models of Lucas magneto (such as the GJ4 I am currently working on) and many other makes of magneto (such as the Bosch discussed in this series) do not include an internal keeper. Their magnets will lose a significant amount of strength the first time they are made keeper-less. That is presumably why the Lucas workshop instructions on remagnetisation of magnetos generally, which cover a vast range of Lucas models including those without an internal keeper, make the point that sometimes it is necessary to remagnetise after an armature has been removed.

It is therefore important, when remagnetising magnetos without an internal keeper using an internal remagnetiser, to apply a keeper before the magnetising core is removed, and to keep the keeper in place until after the armature has been replaced. That is what we do, and the result is as good as can be achieved using an external remagnetiser.

Of course, there are huge benefits of an internal remagnetiser, which is far less wasteful of copper, iron, money and bench space. Going by the wire gauge and resistance of Magnetoman's rig, and if my calculations are correct, it includes about 30 kg of copper. By comparison, an internal remagnetiser core takes about 300 g. Magnetoman's rig weighs 'several hundred pounds', whereas an internal remagnetising core weighs less than 2 pounds. And yet both can drive a magneto's magnet fully into saturation.

Ken
Brightspark Magnetos

#461723 - 11/03/12 3:20 pm Re: Restoring a Rotating Armature Magneto [Re: Ken Tee, R.I.P.]  
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Originally Posted By: Ken Tee
but, in the debate, Magnetoman likes to quote from authoritative sources to support the points he's making.
Yes, I provide facts that can be independently checked, not unsubstantiated claims. My only interest in writing these posts is to provide what I believe to be correct information on a subject where much mystery and misinformation exists. It takes me a lot of time to write these posts, and I make no money as a result of their content, so my only "gain" is knowing I've provided useful information.

Magnetos are quite complex electromagnetic devices, so it would be impractical here to provide all possible background information. For example, the 7th ed. of 'Automobile Electrical Equipment' alone has four chapters devoted just to magnetos, plus relevant material in various other places in this 450 page book. I've included citations to authoritative sources in this thread where appropriate to supplement what I've written, so anyone with the interest can look further into the matter. Again, the reason for the cited references is they contain facts that people can check for themselves, not unsubstantiated claims.

Originally Posted By: Ken Tee
were you telling the truth or an untruth? Please don't come back with more hundreds of words of bluster. A simple one-word answer please, "truth" or "untruth".
To phrase an accusation in the form of a question makes it no less an accusation. It is acceptable in any discussion to point out what you believe, correctly or incorrectly, to be an error. It is never appropriate to call someone a liar. To do so is bad enough by itself, but to do so without even pretending to provide a fact to support your false accusation is grammar school behavior. Unless you delete your post and issue an apology, you will get no answer from me to any question you ask.

Note to everyone else: I see that the post Ken Tee wrote after accusing me of lying about magnetos is another thinly-veiled advertisement in the guise of information. Even though it contains substantive errors, I don't plan to take the time to respond to anything from him.

#461855 - 11/04/12 2:32 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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REASSEMBLY, REMAGNETIZING, AND EXTENDED STRESS TESTS (CONTINUED):

Strobotac

I normally run long-term magneto tests at 2000 rpm (4000 rpm engine) because I want to generate a high internal voltage to reproduce what the coil will experience in later operation, as well as to put the largest number of "miles" on the magneto as fast as possible to reveal any problems. However, it's unlikely a 1920s Harley-Davidson V-twin will operate at 4000 rpm, so this magneto might not be designed to spin at 2000 rpm without the points bouncing. The reason this is a concern is shown in the next photograph.



On the left is the Bosch ZEV magneto and on the right is the Lucas KNC from my BSA Gold Star (note: I flopped the photograph of the KNC by 180-deg. to give it the same rotation sense as the ZEV, which is CCW when viewed from this end of the magneto). The KNC magneto spins to at least 3000 rpm (6000 rpm engine) and, at first glance, it might appear to have a more massive moving point assembly than the ZEV, so perhaps 2000 rpm will be fine. However, closer inspection shows that this initial impression is false. Most of the massive-looking KNC assembly is made of lightweight phenolic, while the entire ZEV assembly is solid steel. I didn't weigh them, but since steel has a density 7x higher than phenolic, a simple estimate is the moving point in the ZEV weighs 3-4x more than that in the KNC. This means that even 2000 rpm might be a problem for these points.

To see if this was the case, I installed the magneto on my long-term tester, removed the cover from the cam assembly (holding it in place with my hand, since the cover spring no longer was doing that), and used a General Radio Strobotac to watch the operation to see if everything was moving as it should.



Setting the strobe to precisely the rotation frequency of the magneto "freezes" the motion. Setting the strobe to a slightly different frequency makes the points plate appear as if it is rotating forward or backward in slow motion. This slow motion effect makes it easy to closely examine the operation everywhere throughout the entire 360-deg. of rotation, or to freeze it at any point, in order to spot any problems with the mechanical motion. This is why I always do this test. The next photograph shows that indeed there is a problem trying to make this magneto run at 2000 rpm.



For this photograph I had set the strobe to freeze the motion just after the points have been pushed open by the cam (rotation is CCW viewed from this end of the magneto). The reason it appears the points gap is quite a bit larger than it should be is because it is. The inset shows why this is the case. The rubbing block is "floating" above the cam because the inertia from its heavy mass has overwhelmed the ability of the spring to keep it in contact after encountering the ramp at this speed. This is the same phenomenon as valve float, except there is no piston nearby to wreak havoc. Unfortunately, this means I either will have to double the pressure by adding the spring from my ZE1 (as discussed in the previous post), or take the time fabricate a larger pulley to reduce the operation speed on my long-term tester. I decided to do the latter.

Another problem the strobe helped me spot, that I had not noticed earlier, is the spring comes within only a few thou. of touching the cam twice per revolution. Although I could slip a piece of paper between the spring and the cam at the distance of closest approach, which means they weren't actually touching, they were too close. I looked at the assembly in my ZE1 and saw the short "helper spring" that is on the inside of the main spring and attached at the 5:00 end in the above photograph instead is at the 11:00 end in my ZE1. Although I had no way of knowing if its location in the ZE1 is the correct one, after I moved it in the ZEV the clearance improved significantly. This seems to be yet another mistake to add to the long list of mistakes the restorer made when rebuilding this magneto. Send questions or comments to classic.vehicle.electrics@gmail.com.

#461871 - 11/04/12 3:58 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Originally Posted By: Magnetoman
Another problem the strobe helped me spot, that I had not noticed earlier, is the spring comes within only a few thou. of touching the cam twice per revolution. Although I could slip a piece of paper between the spring and the cam at the distance of closest approach, which means they weren't actually touching (which would have shorted the armature), they were too close. I looked at the assembly in my ZE1 and saw the short "helper spring" that is on the inside of the main spring and attached at the 5:00 end in the above photograph instead is at the 11:00 end in my ZE1. Although I had no way of knowing if its location in the ZE1 is the correct one, after I moved it in the ZEV the clearance improved significantly. This seems to be yet another mistake to add to the long list of mistakes the restorer made when rebuilding this magneto.

Sorry to interrupt, but in the interests of correcting misinformation, I think you'll find that, in that Bosch set up, the cam ring is at housing earth, and the contact-breaker back-plate, spring and moving point are all at armature earth. So if they touched, the only thing which they would short out would be the earth brush. They would not short the armature.

But of course the spring touching the cam would be a bad thing because of the resultant wear.

The Lucas 'low-inertia' CB assembly in the other photo is a different kettle of fish. There, the spring touching the cam would indeed short the armature.

Ken

#462397 - 11/08/12 11:44 am Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Magneto man, this has been a very educational thread, thank you for posting the beautiful pics and explanations. The strobe shots of the points bounce is very illuminating, it does look like there is a fair bit of extra material on the points moving arm with a lot of scope for judicious weight reduction especially compared with the Goldie points set up.

It is not clear to me how the Bosch points arm pivots, is the fulcrum point beneath the rounded tapering plate secured by the brass top hat washer, is it possible that the pivot bearing could introduce stiction and exacerbate the points bounce?


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#462409 - 11/08/12 4:11 pm Re: Restoring a Rotating Armature Magneto [Re: gavin eisler]  
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Originally Posted By: gavin eisler
Magneto man, this has been a very educational thread, thank you for posting the beautiful pics and explanations.
Thanks very much for your comment. I've spent a lot of time trying to make sure the information is correct and verifiable, as well as understandable by people who may never have seen the inside of a magneto before. I've never seen information at this level of detail on the web or in print on the restoration of a magneto. Of course, this hasn't made everyone who sells magneto products or services happy. I'm reminded that John Wycliffe was burned at the stake for the heresy of having translated the Bible into vernacular English, taking the information out of the sole control of the priesthood to interpret for them. Although some responses have been irritating, it hasn't reached the point of a bonfire being started in my yard.

Originally Posted By: gavin eisler
It is not clear to me how the Bosch points arm pivots, is the fulcrum point beneath the rounded tapering plate secured by the brass top hat washer, is it possible that the pivot bearing could introduce stiction and exacerbate the points bounce?
The pivot is a pin located at the ~10:30 position on the photograph, underneath the almost-vertical clip that has the elongated depression (elevation) in it. The points assembly has a ~1/16"-dia. pin that extends above and below it. At the bottom the pin is a slip fit in a hole in the brass plate. At the top the pin is retained by that elongated depression. That depression could have been a simple hole, but Bosch must have made it elongated to allow for the build up of tolerance (if it were a hole that was not located precisely over the hole in the plate below, the pin would be forced out of alignment and would bind).

Anyway, the points assembly pivots on the pin between the hole in the plate and the clip on the top. I lubed both locations with Lubricam, and at least by feel there was no stiction. That is, I could rock the points open and closed without feeling any resistance. Stiction would provide damping, and thus would help reduce overshoot, not exacerbate it.

The strobe is a very powerful tool for studying magnetos under actual operational conditions. Basically, the strobe lets me study everything in ultra-slow motion. Aside from floating points, if there is any jitter in what I see, that means there is variation due to some sloppy tolerance (which I then can look for and fix). If I were rebuilding a more modern magneto for a racing bike that needed to go to, say, 7000 rpm (3500 rpm magneto), the strobe -- plus different pulleys -- would let me make sure there were no mechanical issues up to that speed. I can't think of another instrument that would provide the same information the strobe does. This is a case where you need to see it, because that's what you're going to get.

#462761 - 11/11/12 2:46 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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REASSEMBLY, REMAGNETIZING, AND EXTENDED STRESS TESTS (CONTINUED):

Long-Term Tester

The reason for conducting an extended test is that, assuming a motorcycle is geared to go ~40 mph at the engine speed corresponding to my test speed for the magneto, a 12-hour test is equivalent to it covering 500 miles. Any teething problems should be revealed in this length of time, but it is not so long that it would cause significant wear on the "new" magneto. In the case of this Bosch ZEV magneto for the Harley-Davidson, I planned to extend the test to 24 hours.

My lathe has continuously variable speeds from 40-2000 rpm so I could use it to spin the magneto at whatever speed I want to within this range for further tests. However, since I run magnetos for at least 12 hours after rebuilding them I don't want to unnecessarily subject my lathe to that much use. So, some time ago I built a dedicated magneto tester using a reversible 1/2 h.p. motor and a universal mounting base that lets me test every type of platform- and flange-mount magneto I've yet come across. With my usual pulley the motor spins the magneto at 2000 rpm (4000 rpm engine). However, after finding with the Strobotac that the points on this magneto float at that speed, I had to fabricate a larger pulley in order to slow it down. Doing this was straightforward, but it ate up valuable time as the deadline for shipping it back approached.

I wanted the new pulley to be ~4" dia. to cut the speed by a third, but didn't have any Al bar that large at hand. So, I bought a 4" pulley from the hardware store, machined an Al rod a thou. oversize to press fit in the pulley's bore (and also held with the set screw), and then used my lathe to bore the necessary 1:10 taper for mounting it on the magneto. With this new pulley the magneto now spins at 1400 rpm (2800 rpm engine), which should be close to the upper limit it will experience on this motorcycle. Checking with the Strobotac showed that the points no longer bounced at this lower speed.



The first thing I found when I started the actual test was that the spark from this magneto was so hot that within a couple of minutes it began melting the plastic insulator on the 6-gap board at the left side of the tester. I got this Merc-o-tronic board on eBay recently and installed it in place of the one I had made myself (the fact I connected it to leads 5&6 instead of 1&2 is irrelevant).



Rather than take the time to reinstall my old gap board, instead I attached the two HT leads to nylon screws that can be seen at the right of the housing in the above photograph of the tester. I then used 0.032"-dia. stainless wires to make 5 mm gaps, corresponding to 6 kV at atmospheric pressure, and continued the test. This voltage is about 50% higher than what will be required to jump the spark plug gap in the operating engine.



At the left of the above composite photograph you can see that ~1 mm of the wire nearest the tip is glowing red hot from the heating caused by the spark current flowing through it (the bluish sheath around the tip is from the ionized plasma created by the high electric field, and the out-of-focus wire from the other lead is in the background). Since each spark lasts only a msec, it's easy to capture an image when it is not sparking, and that is what is at the right. Here it is even easier to see that the tip of the wire is red hot. What this shows is that, even though each current pulse lasts only ~1 msec. and is separated from the next by 35 msec. (i.e. a duty cycle of less than 3%), enough current flows to maintain the tip of the stainless steel wire at ~1000 oF (i.e. the temperature where the steel glows red). Note, though, that a spark plug electrode has both a larger diameter and a higher thermal conductivity than the stainless steel wire, so it would not get nearly as hot as the wire I used for these tests.

Even more dramatically than the glowing wire, if I slip a piece of paper between the electrodes it immediately bursts into flame (it did not touch the hot electrode; it is the spark itself that ignited the paper). Since the sparks from this magneto so easily set fire to paper, I can be reasonably confident they will ignite the mist of gasoline in the combustion chamber.



Elevated Temperature Test

After running the magneto on this tester for 18 hours, I wrapped it in heating tape and heated it to ~50 oC (122 oF) using a Variac, with a thermocouple to monitor the temperature. I ran it another 6 hours at that elevated temperature and it continued to spark reliably. Earlier, in the interest of time, I had skipped testing the armature by itself at elevated temperature, and this 6-hour test of the full magneto vindicated having taken that shortcut. However, had the magneto failed this elevated temperature test due to a faulty armature I would have had no choice but to disassemble it and find the time to wind a new coil myself. I took the next photograph after completing this test and already starting to remove the heating tape. Send questions or comments to classic.vehicle.electrics@gmail.com.


#462769 - 11/11/12 3:42 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Very interesting material MM, thanks for posting.
You must have invested a lot in all this equipment.
Did you ever consider rebuilding magnetos on a professional basis ?


Peter.
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1972 Trident T150T
1961 Goldie DBD34
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#462777 - 11/11/12 4:32 pm Re: Restoring a Rotating Armature Magneto [Re: Peter R]  
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Originally Posted By: Peter R
You must have invested a lot in all this equipment.
Did you ever consider rebuilding magnetos on a professional basis ?
I try not to think of how much money I've spent on instruments, or time on designing and fabricating magneto-specific equipment, fixtures, etc. These posts haven't even shown all of it, because not everything was needed for this particular restoration.

Although I have no way of knowing for sure, I very seriously doubt even the most heavily equipped professional restorer has the equipment and facilities I do for diagnosing and repairing magnetos. As I wrote in a previous post, well over a decade ago I became obsessed with understanding at the most detailed level the operation of magnetos, and cost is no object when feeding an obsession.

As for making money from this accumulated knowledge and equipment, the fact is, I doubt very many motorcyclists would be interested in paying me what I would have to charge in order to make restoring magnetos worth taking the time away from other things that I do.

There will be two more installments in this thread, the last of which I've drafted to help people identify restorers for repairing their magnetos. I won't name names, but will describe what to look for to separate restorers who won't be able to do a good job from those who might be able to (in the sense that you don't necessarily need to know the guy's name to understand that if you're in a bank and you see someone holding a gun that he's probably not someone you should offer to buy a gun from).

#462862 - 11/12/12 2:05 am Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Magnetoman,
I have been very impressed by this thread and have found it helpful, although some has been a little beyond my level. I would like to get your opinion on something. I have 2 bikes with Lucas magnetos, a k1F and a k2f. For years I have been setting the timing by removing the center bolt that holds the points plate, and using a continuity light. i don't remember where I first came upon this method, but it is not in the manuals, and I have not seen it referenced anywhere. Typically, I see references to using cigarette papers or expensive boxes. While the method has always worked for me, the fact that I do not see it referenced anywhere makes me wonder if there is some reason, theoretical or otherwise, why I should not be using it. From your posts, you seem like you might have some thoughts on this method.

Ed from NJ

#462885 - 11/12/12 4:18 am Re: Restoring a Rotating Armature Magneto [Re: edunham]  
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Originally Posted By: edunham
I have been very impressed by this thread and have found it helpful,

a k1F and a k2f. For years I have been setting the timing by removing the center bolt that holds the points plate, and using a continuity light. ... While the method has always worked for me, the fact that I do not see it referenced anywhere makes me wonder if there is some reason, theoretical or otherwise, why I should not be using it.
Thanks very much for your comment. I'm happy to hear you're finding it helpful.

The center bolt performs two functions. One function is as an electrical conductor to connect the points to one side of the primary. That's why removing it lets you use a continuity light. Otherwise the ~0.5 Ohms of the primary would effectively "short out" the light, so it would be lit whether or not the points were open. The other function is to mechanically lock to points plate to the armature. What this means is that if the points plate doesn't twist or move sideways by even 0.001" when the tension on the bolt is removed, the orientation of the armature when your light tells you the points open will be the same as when the bolt is retightened. Otherwise, it won't be, and the timing will be off.

#462915 - 11/12/12 1:04 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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Magnetoman,
Thanks for your thoughts. I think I will add a step to my procedure and make absolutely sure that the points plate is still tight on the taper after removal of the centerbolt and prior to setting timing simply by giving it a wiggle with my fingers.

Ed from NJ

#463824 - 11/18/12 1:42 pm Re: Restoring a Rotating Armature Magneto [Re: edunham]  
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FINAL TESTS:

Finally, we're in the home stretch. This Bosch ZEV magneto has passed all my electrical and mechanical tests so far, giving me good reason to be confident it will be function without problem for some thousands of miles. But, there are still a few more things to check before I am ready to ship it back to the engine builder for installation on the bike.

Low Speed Test

It's great that this magneto works so well at high rpm, but first the bike has to start. So, I next moved it to the lathe, whose continuously variable speed would allow me to run it as low as 40 rpm (80 rpm engine). The point of doing this is to determine the lowest speed the magneto will reliably produce 6 kV sparks with it fully retarded (where it will be for starting).



The photograph shows the magneto mounted on a bracket that I substitute for the lathe's compound and that sits 45 mm below the center line of the lathe. I also have a 10 mm spacer for mounting magnetos having a 35 mm spindle height, as well as a vertical plate with appropriate holes for holding flange-mounted magnetos. Although I don't expect anything in the magneto to seize, the lathe's 1-1/2 h.p. motor could cause quite a bit of damage if it did, which is why if you look closely you will see a short length of plastic tubing is part of the drive train for the magneto. I ran this test for several minutes and the magneto continued to spark reliably across a 5 mm gap down to 135-145 rpm (270-290 rpm engine) with the cam at all positions between fully advanced and fully retarded. A Lucas manual says 300 rpm is a the low end of kick starting speeds, with 500 rpm normal, so the magneto passed this test.

Distributor Tester

My final test used a modified distributor tester to see if during operation the sparks are precisely 157.5/202.5 degrees apart as they need to be for this Harley-Davidson engine, and as my static measurement of the cam profile indicated they should be. However, there are several reasons why under dynamic conditions the firing could be off, or even fluctuate around the correct values, and the only way to know for sure is to measure it. To some extent the Strobotac already addressed part of this issue, since I would have seen fluctuations in the positions of the points when they opened if larger than it a degree or so.

Ten years ago I made several modifications to an Allen distributor tester, including adding an adjustable platform that accommodates both platform- and flange-mounted magnetos. However, when the Bosch arrived the tester had been partially disassembled for a few months to make upgrades to it (actually, most of that time it had been just sitting there waiting for me to find the time to finish), so the temporary configuration I used for this test had the sparks strike just outside the markings on the large protractor. This tester spins the magneto either CW or CCW, whichever is appropriate, at up to 2500 rpm (5000 rpm engine). In addition to testing magnetos with manual advances, like this Bosch ZEV, a digital tachometer allows me to determine the advance curve of a magneto's auto-advance unit, to make sure it is operating properly. I also have adapters that let me check the advance curves of auto-advance units from newer motorcycles that don't have magnetos.

Ideally, the sparks always would happen at the same angles. Since their positions can be easily read to a fraction of a degree on this tester, any variation in spark timing larger than this is immediately apparent. The quantitative results from this tester allow me to decide what further work on a given magneto might be required (e.g. stoning the cam to alter the timing by a specific amount).

The first photograph shows what this tester looks like, although with a ZE1 magneto sitting on the base. The second photograph shows the sparks from cylinder #2 of the ZEV, with the protractor adjusted so cylinder #1 was at 0 deg.






The magneto was running at 1250 rpm (2500 rpm engine) for the above photograph and I used a 1/4-sec. exposure to capture 6 sparks. The protractor is slightly blurred because of vibration of the tester during the long exposure. Although it might appear that the timing was wandering by a degree, the apparent variation is largely an illusion due to the spark finding a different route to earth each time. Note that all the sparks radiate from the same point (to within ~0.2-deg.), which is the tip of the spark wire passing by much too quickly to be photographed with this long exposure (some of the ~0.2-deg. variation could be due to vibration of the tip of this wire in the temporary configuration I used, since the last ~3/8" was unsupported). This test shows that the timing of the magneto wanders by no more than ~0.2-deg. from one cycle to the next. Although this photograph only captured 6 sparks, I watched it closely for several minutes, seeing no sign of problems.

As I wrote in an earlier post, the points for cylinder #2 should open at 157.5 deg. on the magneto (315 deg. engine) for a 45-deg. V-twin engine, but this test shows that the spark is 1.3-deg. early (2.6-deg. engine), at 156.2. Again, this is with the protractor adjusted so #1 is at 0 deg. In terms of engine timing, what this means is #1 would spark that cylinder 2.6-deg. late if #2 were set to fire at the perfect spot. Since the spacing between #1 and #2 on the cam is 1.3-deg. too close (and between #2 and #1 that much too far), it might seem I should improve the timing by stoning a slight amount from the #2 ramp (if they were too far apart, it would require a new cam). However, the static measurement I made on just the cam, described in an earlier post, found it to be good to better than 0.1-degree. This indicates the source of the 1.3-degree problem is a buildup of tolerances of the several components, so grinding one of the ramps would be attacking a symptom rather than the actual problem. And, once ground away, metal can't be put back on the cam.

It bothers me to accept this 1.3-degree error in magneto timing (2.6 deg. engine), and if I had more time I would develop a proper solution, but sometimes perfection is the enemy of perfectly acceptable. The magneto has a manual advance, so if the rider hears pinging from one of the cylinders and retards the ignition until the pinging stops, the other cylinder will be 2.6 degrees further retarded from the optimum timing. However, given the low compression of the engine this magneto will be used on, this will not have a significant effect on performance, especially for its intended use in the cross-country Cannonball Run. Still, even though it won't matter much in practice for this particular engine, it bothers me not to have the time to resolve this.

Disassembly, Inspection, Remagnetization, and Reassembly

After having run the magneto for ~24 hours (~"1000 miles"), I disassembled it to inspect the bearings, measure the brushes for wear, and look for any signs of distress. Everything was fine, so I relubricated the bearings with Sta-Lube high temperature disk bearing grease and the rubbing block with Lubricam, reassembled it, checked that the gap was still 0.012", and then remagnetized it.

Although I previously wrote that running it on the modified distributer tester was the final test, the actual final-final test was to run it for another 15 min. on the long-term tester before packaging it up and sending it back to the engine builder.

Timing a Magneto Using an Inductance Meter

Timing this magneto to the engine wasn't part of the restoration, because that would be done 1500 miles from me after being delivered to the person rebuilding the bike. However, I wanted to at least briefly address how to do this using something quite a bit better than cigarette paper.

There are two aspects of timing a magneto to fire at the right moment. First, the engine has to be rotated to the correct position before top dead center (BTDC) where you want the magneto to fire. Most commonly, this is done at the fully advanced (high rpm) position, rather than retarded (low rpm). Finding the correct position -- most engines are between 30 and 40-deg. BTDC -- can be done to varying degrees of precision with a dial indicator and protractor, a ruler stuck down the spark plug hole, a factory mark on the crankshaft, etc. For the purposes of this post, assume the engine is now at the correct angle BTDC where you want the magneto to fire.

Next, the taper on the magneto's armature is loosely inserted in the gear or sprocket in the engine's timing chest. What you now need to do is to rotate the armature until the points have just opened by the slightest amount, and then tighten the armature to the gear to lock in that timing. Assuming for the purposes of this post that nothing slips when you do this and that there is no backlash in the gear train, the magneto is now correctly timed to have the points open when the engine is at the correct angle BTDC. But, how to find the position where the points have just opened? Forget using cigarette paper.

The resistance across the points of a magneto when they are closed is 0 Ohms, and when open is only ~0.5 Ohms, so a standard ohmmeter would barely register the difference. However, the inductance of a magneto's primary when the points are closed is some number of milliHenries, and when open is some number of Henries, i.e. ~1000x greater. So, an inductance meter across the points will register a huge change the instant the points have separated. Although measuring the inductance might sound difficult, it isn't.

If you search eBay for 'LCR meter' (without the quotes; also try 'LRC meter' for more choices) you will find precision ones go for over $1000. Luckily, though, you don't need precision, so Chinese-made ones that sell for ~$18 (delivered price) are just fine. Attach the leads across the points and set the scale to whatever mH value gives a reading when the points are closed. The actual value is irrelevant, and you don't even have to know the difference between a milliHenry and a megaOhm because all you care about is seeing the meter abruptly go over-range when you slowly rotate the armature. When that happens, tighten the nut to lock the armature to the gear, and the magneto is now properly timed to fire when the engine is at the correct angle BTDC.

Performance of the Magneto on the Road

A month after I shipped this restored Bosch ZEV back to the Harley-Davidson's rebuilder the bike was used in the 2012 cross-country Cannonball Motorcycle Run. Unfortunately, the builder was able to finish the bike only a few days before it had to be transported to the start in New York so there was no time for my friend to give it a proper shakedown. The bike suffered a variety of problems that would have been easy to fix under different circumstances, but that kept it from covering more than ~800 miles over the course of the Run. However, I'm happy to say that the magneto was trouble free. Added to the ~1000 simulated miles I subjected it to on the long term tester before shipping it back, this restored 90-year old magneto has "travelled" nearly 2000 miles without problem thus far. I have every reason to expect it to be good for many thousands more.

This post is the last on the actual restoration of this Bosch ZEV magneto, but there will be one final "Epilog" that I hope will help people identify someone who can properly restore their magneto. Send questions or comments to classic.vehicle.electrics@gmail.com.

#464907 - 11/25/12 4:04 pm Re: Restoring a Rotating Armature Magneto [Re: Magnetoman]  
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EPILOG:

As far as I can tell, at the time of this writing (Fall 2012) this is by far the most detailed description of the restoration of a magneto on the web or in print. Because of this, some additional observations might be useful for people on this Forum as well as those who find their way here thanks to Google.

Basically, there are three audiences for the information in the previous posts in this thread: people who plan to rebuild their own magnetos; people who want their magnetos rebuilt for them; and people who rebuild magnetos for profit. This Epilog is primarily for the second group: people who want help identifying someone who can properly rebuild their magneto.

The Major Problem Areas in Restored Magnetos

Briefly, when magnetos are improperly rebuilt, the subsequent problem(s) they develop most likely result from one or more of the following factors, all of which I have addressed in my previous posts in this thread:

-- Inappropriate condenser
-- Improperly rewound coil
-- Improper (or no) remagnetization
-- Aftermarket brushes that are either too hard or too soft

There can be issues other than these, but these four account for most of the failures I have seen in magnetos that were professionally rebuilt. Because of this, my first recommendation is that you make sure whoever you hire to restore your magneto at least has the tools required to correctly deal with these four issues at a minimum.

Tools

I wrote in the initial installment that my goal in restoring this Bosch ZEV rotating armature magneto was simply to return it to the condition it had when it left the factory. In my experience, to do less than I described in these posts would have resulted in a magneto that was not as reliable, had a shorter life, and/or produced a lower output than it did when it left the factory nearly 90 years ago. The major tools and test instruments shown in this thread that were required to accomplish this were:

--Mechanical--
Mill with digital readout
Lathe with continuously variable speed
1/2 h.p. long-term tester
Modified distributor tester
General Radio Strobotac
Talyrond roundness tester
Bench center with four dial test indicators
Surface roughness tester
Contact breaker pressure gauge
Precision scale

--Electrical--
84,000 A-turn electromagnet
Gaussmeter
500/1000/2500 V megohmmeter
LRC meter
Milliohmmeter
Merc-o-tronic magneto tester
Eisemann magneto tester
[coil winder & vacuum pump-- not used, but would have been had there been more time before the deadline]

--Optical--
Centering microscope
Stereo microscope
Traveling microscope
Metallurgical microscope

Although I have no way of knowing for sure, I seriously doubt even the most heavily-equipped professional magneto rebuilder has the range of equipment and facilities I do for diagnosing and restoring magnetos (not all of which were needed for this Bosch ZEV). But, not all of this equipment would be needed for many rebuilds. So, which of the above tools would someone not need if they only planned to "restore" a magneto as "efficiently" as possible? That is, what is the minimum set of major tools that a rebuilder would need to return the majority of faulty magnetos to customers in a condition where they appeared to function properly when removed from the shipping box?

If the screws in the armature of this Bosch ZEV had not been broken, microscopes and a mill wouldn't have been needed. Although I used the lathe and mill to help remove the epoxy, if someone just wanted to get the stuff out they could have used an acetylene torch instead (I'm definitely not recommending this, but I have seen armatures where the restorer had done this). Anyway, under these conditions, the only tool from the above list actually required would have been an electromagnet. Further, if someone only worked on post-1930s magnetos containing Alnico magnets, even that wouldn't be essential in order for the "restored" magneto to spark when turned with an electric drill (albeit, with a significantly weaker spark than it should have). The point being, there is a huge range of equipment, expertise, and time required between being able to claim to "restore" magnetos, and actually being able to restore them to the reliability and performance they had when they left the factory.

As a recommendation, since even the most straightforward rebuild will require the following, you should not consider sending your magneto to anyone who does not, at the very minimum, have a:

-- 65,000+ A-turn electromagnet (can be less powerful for older, pre-Alnico, magnetos)
-- 2500 V megohmmeter
-- Merc-o-tronic, Eisemann, or equivalent magneto coil tester

I can think of five people who posted to Britbike Forum over the last six months who said they do magneto repairs as part of their business. There was enough information in the posts of four of them for me to see that they do not meet even these minimal requirements, illustrating that by no means is everyone who claims to be able to repair magnetos actually able to do a proper job of it. It also illustrates why such a large number of "professionally repaired" magnetos fail.

Magneto Repairers

There is no accreditation board for magneto repairers, so anyone can claim to be an expert. One YouTube video shows a magneto being turned with an electric drill and the "expert" declaring -- quite incorrectly -- that the intermittent spark it develops at higher rpm indicates it needs to be remagnetized (the problem almost certainly is due to a bad condenser). Neither does a Consumer Protection Agency evaluate advertising claims for veracity. For a number of years one well-known supplier sold replacement condensers with the claim "Modern substitute, very high specification, zero failure." Despite this claim, many failed in service. Ignoring self-proclaimed statements of expertise or reliability, if you are looking for someone to restore your magneto, at a minimum you should determine if they have the necessary equipment to do a proper job (described in the previous section). That alone will eliminate a significant number of possible rebuilders from consideration.

Unfortunately, even if someone owns equipment more advanced than an electric drill, it still may not be obvious whether or not that equipment is appropriate. For example, a well-known magneto rebuilder has a web page showing the equipment he used to rebuild a post-WWII magneto, with one photograph showing it being remagnetized. The commercial magnetizer shown being used for this does not have the necessary field strength to fully magnetize Alnico, which means that magneto was returned to the customer with sub-standard performance. The same is the case for a small "internal magnetizer" another firm inserts in place of the armature. Irrespective of what field that magnetizer is able to produce, the moment it is removed from the magneto the reluctance of the circuit changes significantly. For reasons explained in references cited in earlier posts, this change in reluctance forces the working point on the Alnico's B-H curve to shift, resulting in permanent partial demagnetization, in turn resulting in sub-standard performance of the magneto (i.e. 20-30% reduced output).

The component that is responsible for most failures of rebuilt magnetos is the condenser. Given the countless magnetos that have failed because rebuilders used inappropriate condensers, coupled with the dismal history of false claims from suppliers like "Modern substitute, very high specification, zero failure," I strongly suggest you determine what condenser the rebuilder uses. As I wrote in an earlier post, the condenser I used in this Bosch ZEV was a pair of Panasonic polypropylene film/foil capacitors. I used these capacitors because the manufacturer rates them for high pulsed currents as they will experience in a magneto, they passed extensive environmental and electrical stress tests described in a two-part article in the Fall and Winter 2011 issues of 'The Antique Motorcycle', and they are the only replacement capacitors I am aware of that have passed such stress tests. However, if it were not possible for the rebuilder to get these particular ones, other film/foil capacitors (retail cost ~80 cents) have similar electrical specifications, so alternatives exist for installation in the original location in the condenser cavity. In any case, I recommend that you do not send your magneto to any rebuilder who uses a ceramic chip capacitor (retail cost less than 10 cents) that is packaged by one supplier for use in the points housing.

Armature Winders

If your magneto needs to have its armature rewound, chances are the person doing the restoration will arrange to have that work done by someone else. This is perfectly fine, except…

Although various people offer this rewinding service for ~$150, I spent considerably more money than that to buy my own coil winder, pump, etc. in order to wind and vacuum impregnate armatures myself. As just one of many examples for why I did this, a rewound armature supplied by a well known rebuilder repeatedly seized in the 2010 Cannonball Run due to him having used improper resin to encapsulate it, which continued to ooze for several days. No doubt some rewound coils are made to proper standards, but many are not, and there is no way to look inside the coil of a completed armature to see if it was wound with appropriate insulation and has correct encapsulating resin in the right locations.

Despite the rewound armature that came in this Bosch ZEV having passed all my tests, there is no way to test for possible slow abrasion of the insulation due to relative motion of the wires that could happen if the coil had not been properly vacuum impregnated. Although I judged the chances of failure of the coil as not large, this is the only aspect of this rebuild where I had any uncertainty. As a result of it, I breathed a sigh of relief when my friend called me from the finish line in San Francisco.

Coil winding is such a fiddly job that I would gladly pay someone $250 to do it for me rather than doing it myself. Unfortunately, after having seen a number of rewound coils, I concluded that winding them myself was the only way I could be sure the magnetos I restore will be at least as reliable as they were the day they left the factory. It takes me at least one long day without interruption to set up the equipment, remove the old windings from an armature, wind new ones, vacuum impregnate the coil, and put everything away again. However, if winding armatures were my only job, I can imagine the continual practice would allow me to wind them in maybe two hours (or even less) rather than a full day.

Magneto armatures have been around for more than a century so you would think that by now it should be very well established how to wind them correctly. As late as the 1950s magnetos were produced by the thousands every year just to supply British factories, so techniques of mass production resulted in excellent reproducibility and reliability. Today, though, the winding of magneto armatures is a cottage industry, done one at a time by people working alone and without any independent quality control. To repeat something I wrote in an earlier post, "there is a difference between hand made, and home made." This alone explains why many rewound armatures fail in service. Also, it is clear from what I have seen that many armature winders simply don't understand that there is a lot more to winding a reliable armature than putting many turns of thin wire on top of fewer turns of heavier wire.

The relative number of turns in the primary and secondary determine the output voltage, but the windings ratio is just one aspect of a proper armature. Other essential aspects include the total number of turns of each coil, not just the relative number; thickness of the wires; type and thickness of insulation on them (the insulation on "magnet wire" sold today is available in four thicknesses and at least seven different classes of material, not all of which are appropriate for use in a magneto, with breakdown voltages differing by over a factor of 4 -- and there's no guarantee someone isn't winding their coils using 50-year old spools that has obsolete and age-degraded insulation they bought cheaply on eBay); type and thickness of insulation wrapped over the core and between the layers; type of resin used to encapsulate it (i.e. not just that it has enough viscosity not to ooze out, but that it completely fills all the voids and fully hardens to eliminate all movement of the wires); and whether it was properly vacuum impregnated (which itself requires more than just applying a vacuum to the armature).

Despite my experience with the poor quality of some of the rewound coils being produced, in trying to prepare for possible eventualities I might face I contacted one well-known firm to ask them their turn-around time for rewinding a Bosch ZEV armature. Since I knew it would be difficult to find the time to wind a new one myself if the magneto arrived with a bad coil, I wanted to know if there was another option. When I contacted the firm I also wrote that I would test their rewound coil for a number of hours at 120 oF on my Wiedenhoff magneto tester before installing it and, since I would be working to a deadline, I wanted to know their policy on refunding money if the armature failed (rather than offering to rewind it again, since there wouldn't be time for that). I don't know if it was because I mentioned having my own coil tester, but I never received a response.

Unfortunately, the possible need for a rewound armature makes the restoration problem two levels deep. Not only do you have to find someone with the tools and expertise to properly rebuild your magneto, that person has to have the expertise to identify someone else who properly rewinds armatures. Of course, both good and bad magneto restorers will assure you that the person who rewinds the armatures for him does an excellent job. Maybe they do, but odds are they do not. I realize few people reading this will have an interest in winding their own coils, and I wish I could offer a constructive suggestion here, but all I can do is offer this information on coil winders as an observation.

How Much Should it Cost to Have Your Magneto Rebuilt?

So, how much should it cost to have someone properly rebuild a magneto? The good news is your magneto again can be as reliable as it was when it left the factory. The bad news is, it can't be done for $150.

I didn't keep track of the hours I spent on this Bosch ZEV because I was doing it for a good friend and had no intention of charging him for anything. Also, I had never worked on a ZEV before, so I had to spend additional time researching obscure screw threads, and machining a fixture and pulley specifically for it which, if I were doing this as a business, already would be in hand. Also, if I could have worked on it full time from start to finish it certainly would have been more efficient than piecing together a few hours at a time between trips. With this in mind, how long would it take for a fairly straightforward rebuild of an ailing rotating armature magneto that had been "professionally" rebuilt before, but whose armature hadn't suffered at the hands of the rebuilder as much as this one had?

No matter what, count on having to spend time removing the globs of epoxy that almost certainly would be holding in place the inappropriate condenser the rebuilder had used, in order to make room for a proper replacement. Doing that, skimming and preparing the surface for the earth brush, truing the slip ring, adjusting the end float, etc. all take time beyond just replacing brushes, greasing bearings, and bead blasting the body (even if what's inside is a bodge, magneto restorers always make sure the outside looks pretty, because that's how 95% of their customers will judge whether or not it has been properly restored). Assuming the coil did not need rewinding, my guess is a magneto in reasonable condition would take me the better part of a full day to rebuild to the same "as-new" standards as this Bosch ZEV. This includes conducting the necessary measurements and tests described in these posts (but not counting the hours chugging along by itself on my long term tester).

It should be clear from the posts that doing such work properly is skilled labor, and it requires specialized tools and instruments as well as expertise. One yardstick for cost might be the $85/hour that a machine shop in my town charges. At that rate, the labor alone to properly rebuild a magneto would be ~$700. Although this may seem high, I would have to charge at least that much if I were willing to take on the work. Other than perhaps a few Brough-Superior and Vincent owners, I doubt there would be many motorcyclists ready to pay that (owners of expensive classic automobiles might be more plentiful). Even if you think I am wildly off on my time estimate, and that it actually only would take four hours, that still would be $350 plus parts. But, having said that, I don't believe anyone could restore a magneto to as-new operation in only four hours, no matter how efficiently they were able to work. Even if someone who was skilled enough to command higher wages were willing to work for only $40/hour (which also has to cover health and business insurance, retirement savings, rental of space, and repair and replacement of equipment), and even if they could do a professional job in only six hours, that's ~$250 for labor. Again, these figures all assume a magneto that was in reasonably decent condition to begin with.

Cosmetics

I restored this Bosch ZEV for use in a motorcycle rally, so I spent no time on its external appearance. Had cosmetics been important, just soda blasting the alloy and painting the magnets would have added at least an hour. However, a full concours restoration would have required sending fasteners out for replating (after spending time polishing them), polishing brass and alloy, and finding better-looking HT pickups (or spending time making the current ones look much better). To do this would take more than a few hours and could double the estimates given in the previous paragraph. Again, this is just for the labor.

Final Comments

Even with the proper equipment a rebuilder still needs expertise, but that's harder to verify, and recommendations mean almost nothing in this area. There are a lot of unqualified people doing poor jobs rebuilding magnetos, but who get good recommendations despite magnetos that routinely fail. As an aside, I'm amazed at the number of times I've heard people recommend the person who rebuilt a magneto for them that subsequently failed. I'm not a psychologist, but this seems to be some form of the Stockholm Syndrome. To paraphrase Bruce Springsteen's 'Magic' one final time, as far as magneto rebuilders are concerned "trust none of what you hear, and less of what they claim."

Although I am sure qualified people do exist, I would have to personally know someone's work before I could recommend them as being able to properly restore your magneto. However, in your search for that person keep in mind that it is not that you get what you pay for, it's that you very seldom get more than you pay for. Even though a $150 quote for labor is highly unlikely to get you a $750-level rebuild to as-new performance, paying $750 still may only get you a bead-blasted housing that disguises a $150 repair of dubious quality. To end this thread on a positive note, when looking for a magneto rebuilder, Trust, but verify. Send questions or comments to classic.vehicle.electrics@gmail.com.

#466079 - 12/03/12 10:23 pm Re: Restoring a Rotating Armature Magneto [Re: triton thrasher]  
Joined: Nov 2011
Posts: 3,971
Magnetoman Online content
BritBike Forum member
Magnetoman  Online Content

BritBike Forum member

Joined: Nov 2011
Posts: 3,971
U.S.
If you go to the top of the first post in this thread you will see I've just added a Table of Contents to make it easier to find the information in the individual posts. However, I couldn't figure out how (or if) this Forum encodes hyperlinks to individual posts. If someone can tell me how to do that, I will be happy to update it to make it easier to jump to any post of interest.

#466209 - 12/04/12 7:31 pm Re: How to link to individual posts [Re: Magnetoman]  
Joined: May 2010
Posts: 2,547
TR6Ray Online content
BritBike Forum member
TR6Ray  Online Content

BritBike Forum member

Joined: May 2010
Posts: 2,547
Illinois, USA
Originally Posted by Magnetoman
If you go to the top of the first post in this thread you will see I've just added a Table of Contents to make it easier to find the information in the individual posts. However, I couldn't figure out how (or if) this Forum encodes hyperlinks to individual posts. If someone can tell me how to do that, I will be happy to update it to make it easier to jump to any post of interest.


I'll make no claim that this is the best method to link a specific post, but it does work. I'll use blue font (like this) for the steps to be followed, so they stand out amongst the rest:

{Edit: Due to the havoc wrought by Photobucket in destroying all their picture links and due to the updated format of this BritBike Forum, all the instructions that I once placed here to help MagnetoMan have gone obsolete or missing. In case someone might find it useful, I updated the info on 9/01/2017. I used a different example thread, because MagnetoMan's pictures fell prey to the evils of Photobucket and disappeared.}
_____________________________________________________________

Find the existing post that you want to reference. (It will be more convenient to open a second browser window to do this.) With that post on the screen, point your mouse arrow to the Post Number at the upper RH corner of the box. For example, suppose you want to add a link to a particular post within the thread, "1964 TR6/R Resto" as shown here:

[Linked Image]

Now, RIGHT click the Post Number. When the dialogue box opens, LEFT click the "Copy Link Location" command to copy the desired link onto your windows clipboard, like this:

[Linked Image]

Now, in your "New Reply" dialogue box (using the Full Editor), LEFT click at the spot in your text where you want to place the link. With the cursor flashing at the correct spot, LEFT click the link icon at the top of the dialogue box (see below):

[Linked Image]

When the dialogue box opens, RIGHT click in the text field (there's only one, so you can't go wrong):

[Linked Image]

Another dialogue box will open.

[Linked Image]

LEFT click on the "Paste" command. This will paste the link from your windows clipboard into the field in the dialogue box. Immediately, another dialogue box will open and prompt you to type in whatever info you want to actually appear on the screen as the label for your new link. In this case, I'll type in, "1964TR6/R Resto".


[Linked Image]

After you name your link, LEFT click the "OK" button. That's it, your link will appear in your Posting form dialogue box. Because of the format now used in BritBike Forum, your link will not be underlined like my example one below. I find it easier to recognize a link when it is underlined, so I edit mine to appear that way. If anybody is reading all of this, can't figure out how to underline their links but would like to, send me a PM and I will add that info here.

1964 TR6/R Resto

HTH

Ray

Last edited by TR6Ray; 09/01/17 8:26 pm. Reason: Updated to fix problems caused by Photobucket and to reflect the updated format of BritBike Forum.

'64 TR6R Plus some Twins from other countries (U.S., Germany, Japan)
#466218 - 12/04/12 8:52 pm Re: Restoring a Rotating Armature Magneto [Re: TR6Ray]  
Joined: Nov 2011
Posts: 3,971
Magnetoman Online content
BritBike Forum member
Magnetoman  Online Content

BritBike Forum member

Joined: Nov 2011
Posts: 3,971
U.S.
Originally Posted By: TR6Ray
I'll make no claim that this is the best method to link a specific post, but it does work...
Thank you very much. With three windows open, and only a few screwups along the way, the thread now has a "live" Table of Contents. It should make it a lot easier for people to find whatever they might be looking for without having to scroll through all sorts of nonsense to try to locate it. Again, thanks very much for the detailed instructions (which I kept on screen the entire time in one of those three windows).

p.s. I tested about half the links without finding any issues. But, of course, if anyone finds a problem, please let me know so I can fix it.

Last edited by Magnetoman; 12/04/12 9:09 pm. Reason: restored original "subject" line to avoid confusion
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