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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775277 05/31/19 8:07 pm
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Well, the problem is that the timing slipped yet again. I've never had this problem before but this time I'm going to lap the tapers much longer than I did before, and with finer grit. Then I'll use a torque wrench when attaching the pinion, which is something I've not done before. If that doesn't work, there's always the TIG welder...

Prompted by edunham's and George Kaplan's posts I made a bespoke timing stick much like the one I made a year ago for my Ariel. While visions of slipped pinions danced in my head, for the 'Competition' I made the stick with notches at 39-deg. and 20-deg. which, with TDC also found with the stick, allows for a good estimate the amount of slippage. Of course, the actual problem isn't to measure the amount of slippage, it's to eliminate it.

Attached Files TimingStick.jpg
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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775290 05/31/19 9:22 pm
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You can bell mouth a taper when lapping. If the grit is too evenly spread, the OD cuts more than the ID.


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775298 05/31/19 11:34 pm
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Every time I have had a taper on mag that didn’t hold, it was either because of something I did or didn’t do the last time I was in there, or because something else was wrong. Washer missing on the advance gear, that sort of thing. My only point is that before you go all medieval on the taper, make sure it wasn’t something simple.

Ed from NJ

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775299 05/31/19 11:45 pm
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I can't say that I have known a taper to have slipped like that, especially after having been lapped by a careful practitioner such as yourself, MM. I wonder if the female taper is bottoming out somehow, preventing the mating surfaces from contacting fully? I've seen this happen if the small end of the male taper is slightly large, and/or extends too far into the pinion's female taper.

I've seen several armatures that must have had this problem, because someone had cut back the small end of the male taper. Some manufacturers used to include a thick washer between the pinion seat and the securing nut to ensure the nut did not bottom out on the start of the male taper. May not be your issue, but worth checking.

.. Gregg


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Re: Correct needle for 1000-series Concentrics? [Re: gREgg-K] #775305 06/01/19 12:42 am
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Hi MM,
Quote
Well, the problem is that the timing slipped yet again. I've never had this problem before but this time I'm going to lap the tapers much longer than I did before, and with finer grit.


Selective memory loss ???? LOL (your Ariel)

If Ed and Gregg's comments are not the problem
I'll bet the magneto drive shaft is turning relative to the armature, I have come across this problem a number of times before
I have seen more than a handful of rough tapers that give enough grip to drive a magneto without trouble
perfection is not needed,


John


Last edited by chaterlea25; 06/01/19 12:47 am.
Re: Correct needle for 1000-series Concentrics? [Re: gREgg-K] #775313 06/01/19 2:05 am
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Originally Posted by gREgg-K
I wonder if the female taper is bottoming out somehow, preventing the mating surfaces from contacting fully? I've seen this happen if the small end of the male taper is slightly large, and/or extends too far into the pinion's female taper.

<--- snip --->

Some manufacturers used to include a thick washer between the pinion seat and the securing nut to ensure the nut did not bottom out on the start of the male taper. May not be your issue, but worth checking.
I thought something similar. Either the pinion taper may be bottoming out (very hard to see with the magneto in place) or the nut bottoming on the shoulder of the taper / washer too thin. I think MM mentioned earlier that the washer o.d. was previously a little large and was jamming in the pinion.
Time for the bearing blue on the next reassembly?

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775322 06/01/19 3:17 am
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Originally Posted by Magnetoman
Well, the problem is that the timing slipped yet again.
That statement turns out to be incorrect, which is entirely the fault of edunham and Goerge Kaplan because:
Originally Posted by Magnetoman
Prompted by edunham's and George Kaplan's posts I made a bespoke timing stick
If those two hadn't tricked me into making the timing stick I wouldn't have inadvertently left it on the 20-deg. BTDC notch when I looked at the points, and incorrectly reported the timing had slipped. I hope they are ashamed of their mistake.

Originally Posted by chaterlea25
Selective memory loss ???? LOL (your Ariel)
No, the Ariel's issue is burned deeply into my long term memory. However, in that case the points plate slipped on the shaft. It's the pinion slipping on the taper that I've not experienced before. But, as I wrote above, it didn't slip this time, so the problem is something else.

The misfire problem had developed fairly suddenly after more than ten minutes into a run, but it only happened at fairly low rpm, going away at higher rpm as if the spark plug cleaned itself. So, after I pulled the magneto from the bike I installed my largest pulley and put it on the long term tester. The problem quickly revealed itself to be intermittent sparking between the spring and the cam, as shown in the photograph.

The fundamental source of this problem is the taper. That is, when I had it apart a few days ago I didn't think about it as rebuilding the magneto, I thought about it as just lapping the taper. So, I didn't take sufficient care when I reassembled it after the lapping.

OK, tomorrow a complete, careful magneto rebuild is on the agenda.

Attached Files CamLobeSparking.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775337 06/01/19 7:55 am
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Originally Posted by Magnetoman
[quote=Magnetoman]] entirely the fault of edunham and Goerge Kaplan


I shall forever hang my head in shame .

John


Last edited by George Kaplan; 06/01/19 7:56 am.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775379 06/01/19 3:55 pm
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Went through a taper slipping problem years ago. Problem ended for me when I started using a torque wrench to tighten using 20 ft lbs.
I use my old Bultaco spark plug hole vernier for TDC which is spring loaded and works great for finding TDC.
Charlie

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775417 06/02/19 5:22 am
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Hoping to avoid any issues I took great care rebuilding the magneto today, including using new points. I'm not in a great hurry because my daughter has the pickup through Sunday for a dressage event and I want it here as backup until I'm sure I have the issues sorted out.

After rebuilding the magneto I put it on the long term tester to make sure all was well, but there wasn't any spark. I reduced the gap, tried again, and everything was fine. I then magnetized the magneto, put it back on the tester, returned the gap to 5 mm and it sparked like it should. I mention this to point out that removing the armature and replacing it reduces the output. Only remagnetizing it will return it to the as-new performance.

My electromagnet is powered by the nominal 220 V from a socket in the garage, but the voltage on any given day or time varies. Today it got the magnet to 82.5 kA-turns, which is ~18% higher than the upper limit recommended by Lucas (38% greater than the lower limit). Unlike a tachometer, exceeding the recommended upper limit isn't bad since the Alnico simply sheds anything in excess of what it can store.

The spring for the points comes very close to the cam so I set up a strobe in order to follow the motion as the points plate slowly around to look for possible contact. It comes closer than I'd like but there's nothing to be done about it.

The sound of the spark changes slightly when it follows different paths so it's hard to tell if that is what is happening, or if it's missing. So, I hooked up a HV probe to my analog oscilloscope to watch for signs of missing. An iPhone has its limits when trying to take a photograph like this but it shows the principle. The oscilloscope triggers off a pulse and with the time base set at this sweep speed I can see it and the following three pulses. This is constantly repeated so if the magneto failed to fire during the time I was watching it would be obvious in the shape of a dropped pulse.

Attached Files MagnetoTest01.jpgMagnetoTest02.jpgMagnetoTest03.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775475 06/02/19 10:46 pm
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Hi MM,
OK, a not so serious problem so
I am not a fan of the steel back plate points which often display the problem you encountered
A diamond coated needle file (LIdl or Aldi and probably Walmart) will file the hole in the spring to elongate it where it is clamped by the securing screw moving the curve away from the cam ring

John

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775488 06/03/19 12:27 am
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Originally Posted by chaterlea25
Hi MM, I am not a fan of the steel back plate points which often display the problem you encountered
I have several older brass points plates I could revive, but the springs on them seem just as close. But, if you continue reading a few more paragraphs, I've come across another issue.

I'm not a fan of digital oscilloscopes, although they do have their uses. The first photograph shows a string of 41 sparks over 1.2 sec. (≈4100 rpm engine) without a miss, and watching for several minutes convinced me the magneto isn't missing. In case it's relevant, I've run the new set of points on the long-term tester at 2000 rpm for about an hour. I then moved the magneto to my modified distributor tester to check the timing. There, the plot thickened.

As the second and third photographs show, this tester lets me determine the timing of the spark to better than a degree. This is particularly useful for twin magnetos to see if the sparks are exactly 180-deg. apart (or whatever, for a V-twin). However, it's also useful to see if the timing jumps around due to issues with the points.

Unfortunately, as the fourth photograph shows, at higher speed the timing advances by ~5-deg. (10-deg. engine -- nb. from the tester's point of view the rotation is CW). This happens over a fairly narrow rpm range that I judge to be ~2000 rpm (the battery in the tester's tachometer died and I don't have a replacement). That is, below that rpm the timing has the same value as it does at lower rpm, but above it the timing advances by ~5-deg. The exact rpm where this happens isn't important, but the fact it does happen is.

I tried adjusting the points to give them a somewhat different gap but got the same result. It's not an artifact of my tester since I can watch the pinpricks of light from the points at high rpm and see them move to a less advanced value when I turn the rpm down. For the timing to advance the points have to open sooner and at the moment the only speed-dependent mechanism for this that comes to mind is if somehow the initial slope of cam (or a slight bump) is such that beyond a certain speed it "launches" the rubbing block rather than it continuing to follow the cam to the place where it should open.

I have to find the source of this problem and fix it because I certainly don't want the timing to suddenly go from 39-deg. BTDC to 49-deg. when I exceed ~4000 rpm.

Attached Files MagnetoTiming01.jpgMagnetoTiming02.jpgMagnetoTiming03.jpgMagnetoTiming04.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775501 06/03/19 2:55 am
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Interesting..one wonders whether this is repeatable on other magnetos of similar points operation? This might have been a design issue that was never realized?


No generalisation is wholly true, not even this one.
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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775505 06/03/19 5:10 am
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Originally Posted by Kerry W
Interesting..one wonders whether this is repeatable on other magnetos of similar points operation?
I have another Lucas Competition magneto on my Catalina but as you can imagine I'm not inclined to remove it for measurement. Tomorrow I'll look through my inventory of rusty parts in the hopes I might find another cam ring I could substitute for comparison.

The problem with having too much instrumentation is it only highlights problems, it doesn't provide solutions. Sigh...

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775517 06/03/19 11:43 am
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Originally Posted by Magnetoman
I'm not a fan of digital oscilloscopes, although they do have their uses.

Hi MM, may I ask why you dont like them?



Originally Posted by Magnetoman
For the timing to advance the points have to open sooner and at the moment the only speed-dependent mechanism for this that comes to mind is if somehow the initial slope of cam (or a slight bump) is such that beyond a certain speed it "launches" the rubbing block rather than it continuing to follow the cam to the place where it should open.


Could it be the spring that is letting this happen, too weak (or too strong)? Or a combination of the cam profile and spring, could there be some resonant frequency for the cam profile/spring combination at a certain rpm range?

My comments are just really thinking out load rather than knowledge and experience with this issue. I will be interested to see the cause of this.


John

Last edited by George Kaplan; 06/03/19 11:55 am.
Re: Correct needle for 1000-series Concentrics? [Re: George Kaplan] #775523 06/03/19 1:16 pm
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I've seen this phenomenon on my test bench as well. Sorting it out usually requires adjusting the tension of the contact breaker spring using a fixture of the type described by Lucas in their repair manuals.

It seems more likely to happen with the later/so-called "Low Inertia" fabricated steel assembly than on the older brass type.
.. Gregg


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775525 06/03/19 1:35 pm
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If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.


Amateur Loctite enthusiast.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775526 06/03/19 1:37 pm
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It might be an optical illusion, but it seems to me that in the photo copied below, the contact breaker's anti-fatigue feature is assembled incorrectly:

[Linked Image]

It should be inserted between the spring leaf and the post on the contact breaker, and curving inward toward the center of the mag. The photo appears to show the feature between the head of the screw and the spring leaf, rather than under the spring leaf.

As MM says, those "low inertia" contact breakers can be a pain to assemble without having the spring leaf shorting against the cam ring. Shorting that way did not cause loss of spark with the earlier brass type because the spring leaf connected to the brass platform, but it caused leaf wear nonetheless
.. Gregg


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775541 06/03/19 4:19 pm
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Originally Posted by George Kaplan
Hi MM, may I ask why you dont like them?
Digital oscilloscopes process the input in order to display waveforms, in multiple colors, that look great. Unfortunately, this means pesky features like transients usually are eliminated, which is often where clues to misbehavior lie. With a fast analog 'scope like the Tektronix 2465B, whose screen I showed in a recent post, what you see is what you got.

As an aside, in inflation-corrected dollars that Tektronix 2465B analog oscilloscope would sell new today for around $14k whereas their roughly-equivalent digital oscilloscopes sell for only 10-20% of that. The move from analog to digital wasn't because digital is better, it was largely driven by competition from manufacturers offering digital 'scopes with color displays, clean-looking signals, and automatic setup of triggering at a push of a button for a lot less money. Since that satisfied the needs of the majority of customers, it killed analog. It's also why you can find a 2465B on eBay for a lot less than $14k.

I'm not saying digital oscilloscopes aren't useful, because they are. Including three portable, battery-powered units I have four of them. One isn't much larger than the size of a credit card and, although it is very limited in what it can do, it's been with me on at least three trips to Ireland where it collected useful data on several magnetos. Also, a very useful feature of my benchtop digital 'scope is its ability to display an FFT, which is a crude, but quite useful, substitute for a spectrum analyzer. A digital oscilloscope is way better than no oscilloscope, but for troubleshooting fast transient phenomena I'd hate not to have an analog 'scope.

Originally Posted by George Kaplan
Could it be the spring that is letting this happen, too weak (or too strong)? Or a combination of the cam profile and spring, could there be some resonant frequency
The spring is rivetted to the points so I have no control over its strength. I can imagine why the points might open too late at higher rpm, but I'm struggling to find a reason why they open too early. The fact that the opening position doesn't slowly creep earlier as rpm is increased, but rather moves quickly to a new value over a narrow range of rpm, is an important clue.

Originally Posted by gREgg-K
I've seen this phenomenon on my test bench as well. Sorting it out usually requires adjusting the tension of the contact breaker spring using a fixture of the type described by Lucas in their repair manuals.
I've gone through my Lucas motorcycle and car manuals but didn't see a fixture for adjusting the spring tension. Could you point me to where this information is located? Thanks.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.
I didn't notice any movement of the pin when I installed the new points but I'll check this, and the fit of the points on the pin, today. Thanks for that suggestion.

Originally Posted by gREgg-K
It might be an optical illusion, but it seems to me that in the photo copied below, the contact breaker's anti-fatigue feature is assembled incorrectly:
You passed the eye test with flying colors. In my attempts to locate and eliminate this effect, and to keep the spring as far from touching the cam as possible, I assembled the spring in various ways to see if it made any difference. The photos of the correct assembly were earlier on my iPhone which meant I ran across the incorrect photos first as I worked backwards looking for photos to post. I uploaded those incorrect ones because I came across them first as I worked backwards through the iPhone album and, hey, who would spot the difference?...

Last edited by Magnetoman; 06/03/19 5:51 pm. Reason: another paragraph about digital oscilloscopes
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775545 06/03/19 5:43 pm
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Originally Posted by Magnetoman
<SNIP>The move from analog to digital wasn't because digital is better, it was largely driven by competition from manufacturers offering digital 'scopes with color displays, clean-looking signals, and automatic setup of triggering at a push of a button for a lot less money. Since that satisfied the needs of the majority of customers, it killed analog. It's also why you can find a 2465B on eBay for a lot less than $14k.
<SNIP>

I agree fully with you about digital scopes. The high point of my early design engineering career was when the company gave me a new Tek 465B as my "welcoming gift". During the following 35 years, I had numerous others, but I never got (or wanted) a digital scope. I like the comfort of knowing that what I see on the screen is an analog of what is happening in the circuitry I'm examining ... not a digital interpretation, no matter how clean or pretty. I have a 2465A in my personal lab, and like your 2465B, it serves very well.

Originally Posted by Magnetoman
[/quote]I've gone through my Lucas motorcycle and car manuals but didn't see a fixture for adjusting the spring tension. Could you point me to where this information is located? Thanks.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base, you get that sudden advancing effect when rpm rises.
I didn't notice any movement of the pin when I installed the new points but I'll check this, and the fit of the points on the pin, today. Thanks for that suggestion.

A loose and/or worn pivot pin is a common problem with these contact breaker assemblies. Lucas did not to my knowledge produce a drawing of a fixture to check the spring tension, preferring instead to leave "the how" to the ingenuity of the reader of the specs they published in the magneto Workshop Instructions. I built my own fixture with the back end of a scrap K2F armature, and using a digital "fish scale" to do the measuring. I built the fixture so that one can mount and measure either clockwise or ant-clockwise contact breaker assemblies.

[/quote]

Last edited by gREgg-K; 06/03/19 5:46 pm.

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Re: Correct needle for 1000-series Concentrics? [Re: chaterlea25] #775554 06/03/19 8:36 pm
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Originally Posted by chaterlea25
A diamond coated needle file (LIdl or Aldi and probably Walmart) will file the hole in the spring to elongate it where it is clamped by the securing screw moving the curve away from the cam ring
Done. I already had a box of appropriate diamond-coated Dremel bits for drilling holes in sea shells brought home from Calif. by my granddaughters to make necklaces. As the first composite photograph shows one of them made short work of making the slot longer. The second photograph shows there's now a comfortable distance between the spring and the cam.

Originally Posted by triton thrasher
If the “moving” contact arm is worn loose on its pivot or the pivot pin is loose in the base,
Originally Posted by gREgg-K
A loose and/or worn pivot pin is a common problem with these contact breaker assemblies.
The pivot is quite tight in the base. The third photograph shows that the clearance of the hole in the rubbing block is 0.0015", and in the other two NOS sets of points it was 0.0020", so that doesn't seem to be the issue, either

This time I shimmed the top and bottom of the rubbing block with fiber washers and attached the spring clip to give essentially zero freedom for up/down movement on the pivot pin, but not to restrict its rotational motion. Whether it was the somewhat tighter spring due to the enlarged hole, or the shimming of the rubbing block, this time it no longer jumped to earlier opening as the rpm was increased. It did start sparking at the original (arbitrarily-set) 0-deg. along with ~2-deg. retarded at high rpm, which is much less problematic than changing to too-advanced.

I moved it back to the long-term tester to put an hour on it to make sure everything is bedded in before I'll move it back to check the timing again. Anyway, significant progress has been made.

Attached Files MagnetoTiming05.jpgMagnetoTiming06.jpgMagnetoTiming07.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775555 06/03/19 8:51 pm
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There is something else about this contact breaker assembly that't not quite right:
[Linked Image]



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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775556 06/03/19 8:54 pm
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For how long will your zero end float last, I wonder?

Shouldn’t matter, if the spring was causing the jumping timing effect, of course.


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Re: Correct needle for 1000-series Concentrics? [Re: triton thrasher] #775564 06/03/19 10:29 pm
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Originally Posted by triton thrasher
For how long will your zero end float last, I wonder?
Once the face of the rubbing block is fully bedded with the cam there will be no upward or downward force so the end float shouldn't increase. And a few thou. increase shouldn't matter, anyway.

An iPhone is like a digital oscilloscope, i.e. terrible for capturing transient. I took several dozen photos before I got one that sort of shows what is now going on at high rpm. Visually most sparks are still at 0-deg. but every second or so (i.e. 30 revolutions if it is spinning at an estimated 2000 rpm) a spark happens later. Typically, the late sparks are at ~2-deg. (4-deg. engine) but this photograph happened to capture a spark at ~4-deg. (8-deg. engine). [*]

[*] after another 30 min. spinning at 2000 rpm on my long-term tester the sparks are more stable at 0-deg. with fewer excursions to 2-deg. retarded and none more than that.

If 3% of the sparks are late so the engine produces only, say, ~70% of the power on those strokes it would result in an overall loss in h.p. of 0.9%. I may just decide to suck it up and accept that loss, compounded by the h.p. loss due to having a Concentric instead of a GP.

Question for Gold Star owners to ponder: if my Competition magneto does this, how do you know yours doesn't?

Originally Posted by gREgg-K
There is something else about this contact breaker assembly that't not quite right:
What, pray tell? I've assembled and disassembled it enough times that I couldn't see a huge issue if it was staring me in the face. Which, in the photograph, it is.



Attached Files MagnetoTiming08.jpg
Last edited by Magnetoman; 06/04/19 12:29 am. Reason: quote from gregg-k and [*]
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775630 06/04/19 7:45 pm
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Unfortunately, I'm stuck carefully reading and editing about 50 single-spaced pages of material today so, along with other obligations, time in the garage was limited.

The capacitors for the dead Battery Tender arrived yesterday so I installed one and it has now rejoined the living. While doing this I put another 15 min. of time at 2000 rpm on the magneto. It's unlikely I'll have time to install it today so there's still time for gregg-k to let me know what he sees wrong with the current points assembly.

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