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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775656 06/05/19 6:17 am
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Doing a bit of catch up so I am a bit further behind than normal but is there any reason wht the spring could not be encased in some heat shrink ?
In the past I have seen some points sets where the spring was insulated,


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Re: Correct needle for 1000-series Concentrics? [Re: BSA_WM20] #775666 06/05/19 9:48 am
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Originally Posted by BSA_WM20
Doing a bit of catch up so I am a bit further behind than normal but is there any reason wht the spring could not be encased in some heat shrink ?
In the past I have seen some points sets where the spring was insulated,


I’ve found them taped up before.

It would soon wear through and pressure from contact with the cam might break the spring eventually.


Amateur Loctite enthusiast.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775697 06/05/19 4:32 pm
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Originally Posted by BSA_WM20
is there any reason wht the spring could not be encased in some heat shrink ?
Originally Posted by triton thrasher
It would soon wear through
When I first installed the new points, before lengthening the slot with a diamond tool as suggested by chaterlea, I used a piece of paper between the spring and the cam to gauge the clearance as I rotated the points assembly. At the point of closest approach I had to tug on the paper to move it so the clearance was only ~0.003". That doesn't leave much room for insulation even if the spacing stays the same when rotating at 3000 rpm. Also, both the wear of the rubbing block and of the points will decrease the spacing between the spring and cam so even if the spacing is (barely) fine now, it only will get worse with time.

Once concern is the spark breakdown voltage for plane-parallel plates spaced 0.003" in air is only 600 V (possibly less in the presence of ozone, although a quick search didn't turn up any information on this), decreasing to 400 V at 0.001". This is roughly the voltage across the capacitor in the primary circuit when the points open. But, even if there were room for insulation, would it help? It's actually not an issue since the point that opens, that's attached to the spring, is always at earth potential, as is the cam.

Leaving aside abrasion, given that sparking between the spring and cam isn't possible, the remaining electrical concern is that if the spring touches the cam it would discharge whatever current is flowing in the primary at that time, leaving a reduced amount available for the spark plug. However, that's not actually an issue, either, since the places where the spring could touch the cam come at times when the points are open so no current is flowing in the primary anyway.

So, not leaving aside abrasion, abrasion is the concern.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775708 06/05/19 6:10 pm
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Can the spring be attached to the inner side of the post instead of the outer?


Ed from NJ

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775712 06/05/19 7:32 pm
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Did you ever solve the roller issue? If not try using your lathe and put a deep knurling pattern on them. Even if it doesn't work it will give you a better surface for the adhesive to adhere too.


1951 ZB GS
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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775719 06/05/19 8:17 pm
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Originally Posted by edunham
Can the spring be attached to the inner side of the post instead of the outer?
It could, but the post itself is threaded and it would be very difficult to tighten a screw installed from the inside (and it would be a tight fit for a nut), and it also would add quite a bit of tension to the spring. It's quite possible that the ~0.003" clearance with the new points would have turned out to be fine even in the long run, but it was just too close for my comfort. Lengthening the slot in the spring was easy and it gave enough additional extra clearance to make me happy.

Originally Posted by bsalloyd
Did you ever solve the roller issue?
It turned out to be a "breather issue" rather than a "roller issue." Before I discovered the problem the replacement abrasive paper already had been torn up but even then the rollers have had no problem at all starting the 10:1 engine multiple times. DocZ offers a set of "forever" rollers with slots and powder paint embedded with grit, and I'll probably buy a set once my current jetting experiments are done. They're sold using the current rollers as exchange and I don't want to be without my DocZ until I foresee a few weeks of down time.

You might remember that my friend's shop burned last month. He was able to salvage some things that he moved to space he rented a few weeks later. Today he asked for help rearranging the ten or so bikes (including my A65) that more or less made it through the fire. It's pretty sad. The fiberglass tank on a round-case Ducati looks like a chia pet. The lower yoke on a (formerly) very pretty small Ducati was completely melted into a puddle. He said he had taken a Moto Guzzi home immediately after the fire, before he had the new rented space, but when he looked at it on the trailer the next morning he realized there wasn't a single salvageable piece on it so he hauled it back to the shop to be disposed of.

The Gold Star connection to this is today he gave me a header pipe and twitter silencer he rescued from the rubble. Along with another Innovate LM-1 I picked up for very little because it was mis-listed, I'll now be able to get the jetting sorted out on an ultra-rare twin-port Gold Star should one come my way.

Attached Files DocZ_rollersJune2019.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775738 06/06/19 2:52 am
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It was an interesting day in the lab... er, I mean, garage.

I wrote a very long post immediately after coming in from the garage but decided I need to think about it a bit more so I'm temporarily deleting it. Stay tuned.

Last edited by Magnetoman; 06/06/19 4:29 am. Reason: temporarily removed post
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775739 06/06/19 3:25 am
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Mot being savvy with the operation of the oscilloscope and the data one can produce, one wonders what the makers of magnetos used to determine how their products worked, or didn't? And could they have improved the basic magneto if they did have the modern data? I suppose that question is answered by the development of modern CDI ignitions (by subsequent generations of ignition engineers) ...the first of which had a very short spark duration and weren't that successful.

One also wonders if modern magneto rebuilders go to these lengths to identify problems or check correct functioning? I'm sure some have the knowledge and capability...though surely not all.

KW

Last edited by Kerry W; 06/06/19 3:28 am.

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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775784 06/06/19 5:19 pm
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Originally Posted by Kerry W
Mot being savvy with the operation of the oscilloscope and the data one can produce, one wonders what the makers of magnetos used to determine how their products worked, or didn't?
I decided I wanted to make another measurement to add to yesterday's lengthy, temporarily-deleted, post before reposting it. Meanwhile, the attached figure from the 1933 edition of 'Automobile Electrical Equipment' by Young and Griffiths addresses your question. This book started out c1920 as 'Magnetos', with the renamed book adding chapters around the core of the original.

The figure shows two spark points on what is essentially the same apparatus as my modified distributor tester. The text explains that they observe a bright white flash between the two spark points when the spinning apparatus reaches position A, with a weaker flame continuing for several degrees after that as the apparatus spins further. By knowing the rotational speed and the fact that the bright flash doesn't appear to be "smeared" out they estimated that it must last only ~1 microsecond. This was the instrumentation available to them in 1933 to try to understand how sparks are generated. Today, a 50 MHz high voltage probe connected to a 400 MHz oscilloscope lets me directly "see" the details of the spark at a time scale 50x faster than they could even estimate.

Going even further, I have two high frequency current probes as well so, along with the 4-channel oscilloscope, I can simultaneously watch what is happening at each instant in time to the primary and secondary currents and voltages. This is easier done with a rotating magnet magneto since it doesn't require making electrical contact with a spinning points plate (making that contact isn't too difficult, but doing it without a lot of electrical noise is).

Originally Posted by Kerry W
if modern magneto rebuilders go to these lengths to identify problems or check correct functioning? I'm sure some have the knowledge and capability...though surely not all.
If I were rebuilding magnetos for a living I would have long ago gone bankrupt. I spent hours in the garage yesterday spinning the magneto and taking data, only to think of an additional experiment to run today. Add to that the time I spent changing the points, lapping the taper, and magnetizing it and I've easily been working with it for the equivalent of two full eight-hour days and I'm still not done with it.

I've written before that a bad experience with a magneto restorer 25 years ago set me off on the quest to understand these devices at the most fundamental level possible. As a result of that experience I've assembled what certainly must be by far the most heavily instrumented "magneto research facility" in existence. No rebuilder "needs" instruments to measure resistances from 10 µΩ to 1000 TΩ (1 thousand million MΩ), 6½-digit DVM that can detect the difference between the resistance of the 5000 Ω secondary coil alone and the 5000.5 Ω resistance of it plus the primary coil, 200 Watt 1 MHz pulse generator for stress-testing capacitors, etc. However, having these instruments lets me check functioning and identify subtle problems better than if I didn't have them.

If I regularly rebuilt magnetos as a business, rather than only one every year or so, each one certainly would go faster. However, although magnetos certainly can function well without being tested at the level I test them (or fail even then if a screw isn't Locktited), it's difficult to see how someone could go to the lengths I do to understand and characterize these devices and do so at a profit.

A "living wage" in most of the U.S. is $18/hr. for a family of 2 adults with one working. Coincidentally or not, this is the average hourly rate paid to automotive technicians in my town, even though garages bill at the rate of $80-100/hr. to cover that plus expenses and profit. Someone who rebuilt magnetos at the rate of 2 per week would have to charge $375 ea., plus parts, to reach that wage if it were their sole source of income. The median household income in the U.S. is $61.4k ($235 per working day). If they upped their production to one/day they could drop their price to $235 ea. to reach that somewhat higher standard of living.

Attached Files MagnetoTiming14.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775798 06/06/19 7:33 pm
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These days, if I knew it was being done to the standards above, I'd pay the price...


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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775816 06/07/19 12:04 am
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If you don't like technical topics, let alone long technical posts, now would be a good time to avert your eyes.

It turns out in the absence of a working tach I had significantly underestimated the rpm of the modified distributor tester. I'll come back to that in a moment, but having seen sparks that started coming too early at high rpm I put the magneto back on the long-term tester for another hour. I have the tester on a wooden workbench, and I didn't want to leave it running there while I was away, so that gave me time to make some other measurements.

In an earlier post you can see the spark but you can also see a magenta arc extending 5-7 degrees beyond the spark at whatever rpm was used at that time. So, why the magenta arc? I have a Tektronix high frequency, high voltage probe from the 1970s that is good for measuring 40 kV signals at up to 50 MHz (i.e. time constant 20 nsec). For voltages that high it has to be filled with Freon 114, manufacture of which was banned nearly 25 years ago. However, I have one pint of the precious substance that I'm saving for a rainy day (as if working with 40 kV on rainy days is a good idea...). Luckily, though, the probe is good for 13 kV without Freon. So, I connected it to analyze the signal while the magneto was running anyway.

The two traces of the first photograph show several sparks as seen on the displays of an analog (top) and digital (bottom) oscilloscope. The voltage probe is 1000:1 so each 1 V signal on the oscilloscopes corresponds to 1 kV. It can be seen that the signal repeats after 29 ms which indicates the magneto is spinning at 2069 rpm (1 rev./ 29 ms x 60 sec./min. = 2069 rpm). Starting in the middle of the top trace, what it shows is the voltage at the end of the spark plug wire starts out at 0 V with respect to the housing, abruptly goes negative by some number of kV (to be determined below), recovers somewhat to a skewed plateau value of ~1 kV for ~4 ms, after which it returns to near O V for ~8 ms, then goes nearly 3 kV positive, after which it returns to near 0V until the cycle repeats.

My Tektronix 2465B has the valuable feature of a second time base that I can trigger an arbitrary delay after the main trigger. Although I can display both the main and expanded signals at the same time, it's easier to photograph when I've displaced the main one off the screen and increased the intensity, as I've done for the bottom half of the second photograph. The region where the potential abruptly goes negative is expanded by 50x in the bottom trace, where the horizontal scale is now 100 µs. As can be seen, it takes the potential ~20 µs to get to -3 kV, after which it jumps back to ~-600 V in a time that's too short to be determined from this trace. That is, it takes ~20 µs after the points open for the voltage to reach a large enough value to cause electrical breakdown in the air, at which point the voltage drops "instantly" (i.e. a very short time to be determined below). The ghost traces show that the timing of these features jumps around by ~200 µs which, at the rotational speed of 2079 rpm, corresponds to an angle of 1.2 degrees. However, it's not quite that bad since this jitter depends on where the oscilloscope trigger is set. The modified distributor tester shows the jigger is less than 1 degree (2 degree engine).

Note that the voltage when the spark takes place is negative. This means electrons will be "pushed" from the relatively sharp central electrode of the spark plug and travel to the relatively flat earth electrode. If the magneto were magnetized in the opposite way electrons would be attracted from the earth electrode. Since it requires less voltage to eject electrons from a sharp electrode than from a flat one, this magneto is properly magnetized to initiate an arc with the greatest ease, which is just what you want for starting a 500 cc single. With a twin magneto this effect means one side works a bit better than the other, which only is important when magnetizing a V-twin magneto.

Going 500x shorter in time, to 200 ns/division, the third photograph shows what happens at the instant the voltage reaches the breakdown voltage of air. Basically, the time scale is close enough to the claimed 20 ns response time of the high voltage probe that, without calibrating the probe response with at least a 100 MHz square wave, all it's safe to say is that within no more than 40 ns after the spark was initiated the voltage has dropped to a new plateau value followed by damped ringing for ~800 ns.

As my previous post mentioned, with 1933 technology they estimated the main spark took place in no longer time than 1 µs. The oscilloscope trace shows it takes place in no more than 40 ns, i.e. at least 25x faster than that 1933 estimate.

At 3500 rpm, which is the maximum rotation rate the magneto needs to reach the 7000 rpm engine redline, it makes 58.3 revolutions/sec. The oscilloscope traces show that the lingering arc lasts for another 4 ms after the main arc. If sufficient current remained in that lingering arc for the discharge to remain visible for 4 ms that would be 58.3 rev/sec. x 4 msec. x 360-deg/rev. = 84 degrees. In fact, the visible arc in the fourth photograph lasts only ~10 deg. so by 10/84 x 4 ms = 0.5 ms so that's how long it takes for enough energy to be dissipated that the arc is no longer visible.

The fourth photograph shows the behavior observed in 1933, with a sharp bright spot followed by a lingering arc. Again, the rotation is CW in the photograph.

Because of the limitations of the iPhone camera I had to take ~20 photographs before I captured the dot of light at 351-deg. in the fourth photograph, i.e. well before the points should have started opening. The main spark actually remained at 0-deg. but in doing all of this, including dropping my iPhone when my elbow touched a piece of the tester and received a 2.8 kV jolt, I didn't notice the scale had moved.

The first signs of these dots of light appearing before they should have was at 3100 rpm (6200 rpm engine), with the dots becoming more frequent by 3280 rpm (6560 engine). The fourth photograph was taken at 3340 rpm (6680 engine). Although that dot of light is a spark of some sort, it doesn't have the characteristics of a "real" spark, i.e. it lacks a long tail due to energy from the coil being dissipated. At this point I don't know what those dots of light are. However, since it takes a few mJ of energy to initiate ignition, and since a magneto isn't designed to produce much more than that minimum, and since such a "real" spark results in a long arc trail, it's unlikely those dots of light have enough energy to cause premature ignition.

My long-term tester is much more rigid than my modified distributor tester so I ordered a larger pulley to increase the speed from the present 2000 rpm to a little less than 3500 rpm. That way I'll be able to see the electrical signature of those parasitic dots of light with the oscilloscope. However, I'm inclined to install the magneto tomorrow and save additional measurements for some undetermined time in the future.

Turning to a question raised by George Kaplan, I had time on my hands while the magneto was logging hours yesterday so made other measurements as well. The first photograph shows the sort of square-wave-like behavior around the time of the spark. The bottom of the second photograph is a 50x expanded portion of the upper traced, with the "ghost" lines indicating that part of the waveform fluctuated considerably. What this analog oscilloscope lets me do is simultaneously watch, in real time, the overall behavior while also seeing these fluctuations to observe the actual behavior of the spark.

The top of the fifth photograph shows the same region as in bottom of the second, except on a digital oscilloscope. Clearly, nothing much can be learned from this trace. However, it's not an entirely fair comparison since there are other ways to use the digital 'scope to do better than this. Still, since I own both types of oscilloscopes I have my choice, but I turn to analog for a situation like this.

Two things a digital 'scope can do that often are quite useful are shown in the first and fifth photographs. The bottom trace of the first shows many sparks because the time base is set to a long 10 ms/division. If an analog oscilloscope had a setting much longer than this the initial pulses would have faded from the screen long before the final pulses were registered, whereas a digital oscilloscope -- more accurately known as a digital storage oscilloscope (DSO) -- displays the trace for the full length of the sweep (or, forever, if the 'save' button is pushed). The lower trace is a Fast Fourier Transform (FFT) of the upper trace, which transforms data from the time domain to the frequency domain. The peak heights and frequency spacing between peaks can provide very useful diagnostic information in many circumstances (although not in this case).

I haven't even scratched the surface on the strengths and weaknesses of the two types of oscilloscopes (nor sub-categories, like analog storage oscilloscopes). But, it's horses for courses. For most automotive purposes I find an analog 'scope better, but for some things only digital will do.


Attached Files MagnetoTiming15.jpgMagnetoTiming16.jpgMagnetoTiming17.jpgMagnetoTiming10.jpgMagnetoTiming18.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775828 06/07/19 7:44 am
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Hello MM, thanks for taking the time to do this work and write about it. I read it twice and found it both interesting and informative (to a point due to my level of knowledge and experience with electrical circuits and electronics)

I have a simple question. Taking this data along with everything else that you have learnt about magneto's, what does this tell us in practical terms about:

a) Your magneto and the issues that you were having?

and

b) Magneto's in general and what this tells us about what we should or shouldn't do with them when maintaining/rebuilding or just using them?

John

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775843 06/07/19 1:11 pm
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Good morning, folks,

Many years ago, when MM and I were at our second or third Irish National Rally in County Cork (the 'Munster), MM bravely (or rashly) volunteered to give a talk about magnetos to the assembled throng.

As a pilot of light airplanes, I had long been used to testing magnetos during engine run-ups (there are two mags, for redundancy, in a typical light airplane). And I knew that magnetos in aircraft rarely, if ever, fail. Why? Because they are serviced regularly by mechanics who understand how they work, and what is needed to keep them in perfect condition. MM used this example in the preamble to his talk, implying that if magnetos are so reliable, why do they so regularly 'pack up', in old motorcycles.

The talk was, as you might expect, illuminating, and MM went into detail about coils, primary and secondary, the relationship between magnetism and electricity (Einstein would have been proud), and, most critically, the shelf life of capacitors. One guy in the audience took all this in so comprehensively that he became (and remains) a skilled magneto restorer. Many were enlightened, others amused. But several were downright dismissive. One, a chap who wrote a technical column in a British classic bike magazine, loudly denounced the whole talk as a 'load of bollox'.

And to answer George's question, this information has plenty of practical things to say about how we use our magnetos, day-to-day. But I will leave that to MM to elucidate.

TGIF,

Ultan



1949 BSA ZB34 'Bitsa'
1959 BSA DBD34 Catalina
1973 Norton Commando 850 R
1974 Norton Commando 850 R (I know, one too many)
1975 Honda TL250 Trials, a new addition to the family
1998 Montesa Cota 315 HRC
2004 Ducati M1000ie
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775854 06/07/19 3:38 pm
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Originally Posted by George Kaplan
what does this tell us in practical terms about:
a) Your magneto and the issues that you were having?
and
b) Magneto's in general and what this tells us about what we should or shouldn't do with them when maintaining/rebuilding or just using them?
Keep in mind the basic purpose of any of my posts is simply to tell you what I did. No one said I actually had to explain anything...

You can blame some of the length of my previous post on Kerry W, who had wondered how engineers studied magnetos in the old days. I answered that with Fig. 141 from a 1933 book, but that then caused me to crank up the time base of my oscilloscope to show the answer that a modern instrument gives. Some people (me, for one) enjoy learning that a magneto spark has two components, one that's over in no more than ~40 ns and the other that lingers for several ms (although it remains visible to the eye for only ~0.5 ms). However, it's hard to point to how those specific numbers would affect rebuilding a magneto, other than deviations from them means there's something wrong.

You're to blame for some of the length, as well, since otherwise I wouldn't have digressed to discussing some of the strengths and weaknesses of digital vs. analog oscilloscopes. But, it's hard to point to how knowing those differences would affect rebuilding a magneto.

Returning to your questions, my magneto had worked fine for several hundred miles, with the exception of the pinion slipping on the taper. However, at that point something changed and a misfire developed below ~3000 rpm that went away above that speed. That caused me to remove the magneto and start these recent tests to determine the cause of that misfire and to eliminate it. So, one of the practical things learned from these tests is how to modify the spring to make sure it can't touch the cam. Another practical outcome was that testing the magneto after first installing those points found rogue early sparks above 6000 rpm (engine) that could have had serious consequences. Knowing that properly installed points can result in a potentially engine-destroying problem counts as practical information that came from these tests. Also, it counts that finding that shimming the pivot to give zero end float eliminated that problem.

As NYBSAGUY pointed out, I give hour-long lectures on magnetos with over 60 images, including specific details on diagnosing problems and repairing them. That's way more information than would fit in even a dozen lengthy posts. Also, the information in those lectures is organized in a logical sequence by content, rather than sequentially (and incompletely) by time as it is here.

Reminder: an extensively documented rebuild of a magneto can be found here can be found here where much more information about the practical aspects of rebuilding a magneto can be found than in my previous post in the current thread.

Originally Posted by NYBSAGUY
One, a chap who wrote a technical column in a British classic bike magazine, loudly denounced the whole talk as a 'load of bollox'.
But, to be fair, he had reason to be grumpy. You'll remember that at the lunch stop that day I had fixed a flat for Mike Jackson (of Norton-Villiers and Andover Norton fame). Prior to my magneto lecture that evening grumpy magazine writer was pontificating to a group at his dinner table that modern tubes were made of a material that didn't allow them to be patched. Mike happened to be nearby and corrected him, saying the patch I had made at lunch had lasted the rest of the day (and the rest of the rally, for that matter). It turned out that grumpy writer had patched Mike's tube twice that morning and both had failed in a matter of minutes, resulting in the bike being hauled to the lunch stop in one of the breakdown vans.

Another unhappy listener insisted during the Q&A after my lecture that people shouldn't attempt to repair old magnetos and instead should replace them with reliable modern ones. I learned later that evening that he was the founder of the then-new BT-H company.

Attached Files MJMatchless.jpg
Last edited by Magnetoman; 06/07/19 6:16 pm. Reason: added photo of Mike Jackson (on the right) immediately after the tube on his Matchless was patched.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775858 06/07/19 4:25 pm
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MM & NYBSAGUY, thanks very much for your replies.

Originally Posted by Magnetoman
You're to blame for some of the length,


Blame happily accepted. Without the word "why" we would still be living in caves. Everyone should try to have an inquiring mind and be happy to learn new things (I believe I am preaching to the converted on this point). I am very appreciative of the posts that you make on here and I have read your main magneto post at least twice and referred to certain parts of it more times than that.

So it now seems that you have a magneto that you are happy with so I assume that your Gold Star will be ready for battle soon?

John



Re: Correct needle for 1000-series Concentrics? [Re: George Kaplan] #775862 06/07/19 4:45 pm
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Originally Posted by George Kaplan
I assume that your Gold Star will be ready for battle soon?
The morning coffee has finally started to kick in so I'm about to go to the garage to install the magneto on the bike. By the time I get that done, run an errand, and the breakdown truck driver (AKA wife) returns home it will have hit the first 100 oF high of the season so I might postpone the first test ride (and jetting run) until the relative cool of tomorrow morning.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775871 06/07/19 7:59 pm
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Jetting runs at 100°F builds character........


laughing


Never underestimate the human ability to elevate stupid to a whole new level!.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775885 06/08/19 12:26 am
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Originally Posted by Rich B
Jetting runs at 100°F builds character........
Thanks for that observation, but the shakedown runs I made on my Ariel during a record-breaking heat spell last July built enough character to last me the rest of my life.

The Gold Star is back together, timed, and ready for tomorrow. I started it... well, my DocZ started it, and I made an uneventful lap of the driveway. So far, so good, but fingers crossed that all goes well tomorrow.

Before installing the magneto I ran it on the modified distributor tester and took photos at a grazing angle to give a more 3D feel. Again, it required a number of photos at 3200 rpm (6400 rpm engine) before I caught an early spark. As can be seen the main spark happens at 0-deg. (or ~1/2-deg. before that) and the wayward spark came 5-deg. before that. Also, the long tail of the main spark can be seen to be visible for 12-deg. while the early spark has no such tail, which means less energy was deposited by that spark.

The second photo shows how I have my crankshaft marked to identify TDC. This isn't necessary, but certainly makes timing the magneto a lot easier. I don't have to mess around peeking in the spark plug hole trying to see the valves moving as I bump the rear wheel.

The third photograph shows a genuine Lucas magneto cam advance fitting on the bottom and an aftermarket one on the top. The genuine article has an O-ring and, more important, is a little bit longer. The aftermarket one is barely long enough to insert the ferrule on the cable into it.


Attached Files MagnetoTiming19.jpgTDC.jpgMagnetoCamAdvanceFitting.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775952 06/08/19 11:39 pm
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The goal of all my work flow testing, magneto measuring, carburetor rebuilding, and air/fuel monitoring over the past several months was to see if I could jet a 1036 Concentric to work on a Gold Star without changing the spray tube or drilling the compensating air passage. That is, I wanted to determine if only the simplest swapping of a few screw-in components would make it functional. Today all that work seems to have paid off.

First, some background. The "stoichiometric" A/F ratio for gasoline is 14.7:1. It varies from this depending on the ethanol content so λ is a better parameter to use (but, I prefer AFR so that's what I'll continue using). Maximum power from most 4-stroke engines will occur for A/F ratios in the range 12-13, although for maximum fuel economy a ratio closer to 14.7:1 would be needed. If it gets much richer than 10:1 the mixture can fail to ignite regularly, i.e. the engine will start missing, and if it is much leaner than 14.7:1 the engine can overheat and be prone to damaging pre-ignition.

I made A/F measurements under two sets of conditions, "static" and "transient." I made the former by holding the throttle in a fixed position for ~5 sec. before changing the throttle to a different position. For less than ~1/3 throttle these were made on relatively level ground as well as when going uphill and downhill. Higher throttle settings only were made going uphill to keep the speed within reason given the conditions.

"Transient" measurements were made by snapping the throttle open. I use a 1.55 V battery in my throttle position sensor so the first graph shows a 15-sec. section of the data where I was in 2nd gear at ~1/3 throttle (the red curve), then snapped the throttle closed and back open, shifting successively into 3rd and 4th where I finally gave it full throttle. The magenta A/F curve shows brief lean pulses occurred roughly 1/2-sec. after each of these throttle movements, but none are excessive and I felt no hesitation from the engine. In fact, I couldn't be happier with how the engine felt throughout this entire run today.

As can be seen from the first graph, even in regions where I kept the throttle constant the A/F curves fluctuate by ~+/-0.5 around a mean value. Added to this is the mean value at a given throttle setting at different times during the run (i.e. possibly under different conditions of, say, uphill one time and downhill another) could vary by nearly that much as well. As a result, I've drawn a band around a central line in the second graph to more realistically represent today's measurements.

A few comments about the second graph: The curve starts at an AFR of 12.2 at idle. I set the idle by adjusting the mixture screw to give the maximum rpm and this was the AFR that resulted. As can be seen, below ~1/8 throttle the mixture is richer than it needs to be. Comparing this region with the measurements I made with a #3.5 cutaway I judge that a #4.25 would be slightly better since it would raise the AFR in the valley at ~0.05 throttle. However, I don't anticipate spending much time riding with the throttle barely off idle so the fuel saved by making this change doesn't seem worth the effort.

For throttle settings between 0.2 and 0.5 the mixture is slightly leaner than the "optimum" 12-13 for maximum power. Raising the needle another notch isn't an option because that would make it much too rich in that region. However, there are two reasons I don't think this region is an issue. First, the 12-13 "rule" is just a guideline, and only time spent on a dyno would determine if more h.p. could be extracted with slightly richer mixtures. Second, most time on a machine spent cruising at mid-throttle so having a slightly leaner, but still rich, mixture will save a bit of fuel without costing any actual performance.

Before disconnecting the Innovate setup, re-installing the unmodified pipe, and declaring this episode 'done' I'll make at least one more jetting run to fill in a few additional data points between half and full throttle. However, I had a close call with a sheriff's car today. I had just come down a hill and made a U-turn onto a side street and was waiting for traffic heading up the hill to get far enough along that I wouldn't catch up with them. Had I taken off 5 sec. earlier I would have been going well over 60 mph (with a 35 mph speed limit) when the sheriff's car came around the curve at the top of the hill.

In conclusion: the 1036 Concentric jetting listed on the second graph is perfect-ish for my Gold Star.

Attached Files AFR_8June19_01.jpg
Last edited by Magnetoman; 06/09/19 10:00 pm. Reason: temporily removed Fig. 2. Will repost updated version with today's new data in due course.
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775978 06/09/19 2:33 pm
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The last and only Gold Star I have worked on with a 1036 carb it was jetted

4 stoke jet holder
230 main
needle in middle
25 pilot
106 needle jet
4 stroke spray tube
3 1/2 slide

How would the 2 stroke spray tube with leaner slide compare to the 4 stroke spray tube with slightly richer slide? You have all the stuff hooked up, slap a 4 stroke spray tube and slide in and go for one more ride.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #775986 06/09/19 3:50 pm
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Originally Posted by RPM
How would the 2 stroke spray tube with leaner slide compare to the 4 stroke spray tube with slightly richer slide? You have all the stuff hooked up, slap a 4 stroke spray tube and slide in and go for one more ride.
Unfortunately, I turned one of my slides into a #4 (after initially making it a #3.5) so right now only have one ea. #2, #3, and #4 slides. So, I can't do the measurement needed for a direct comparison with your result. However, I can speculate based on the data I do have.

Actual measurements always are best but, when they're not possible, estimates based on related data can be quite useful. The flow bench results I posted in April showed that at full throttle the 2-stroke spray tube (with unmodified air compensation passage) increases the pressure difference ("vacuum signal") by 21%. That says, all other things being equal (such as the air filter you did or didn't use, which is a big factor), your 230 main would imply mine should have been a 190 to give the same mixture as yours. My 220 gives a rich-ish 12:1 at full throttle so if I swapped it for a 190 the AFR would change to 230/190x12= 14.5:1. A bike should run without apparent problem with that leaner mixture so your main jet and mine are consistent.

The smaller "vacuum signal" from your spray tube also would draw less fuel into the air stream than mine at lower rpm and hence yours would require a richer slide than mine. Again, your slide and mine are consistent.

The difference in "vacuum signal" at 1/4 throttle, where my AFR curve has a broad peak, is 15%. Despite this difference, which is smaller than that at full throttle, your needle is on the same the middle slot as mine. However, the AFR in this region depends on both the cutaway and the needle position so I can't say whether or not this is an inconsistency.

Given the uncertainty in your configuration (i.e. the air filter), and the fairly broad range in AFR where the effect on performance is subtle (i.e. between 11:1 and 14:1), your jetting and mine are consistent. Although my jetting has the advantage that it's backed by actual AFR data, it's worth repeating that they're the best results possible with an unmodified air compensation passage and 2-stroke spray tube, not necessarily the absolutely best results possible (still, my bike runs great with this jetting). I'll end with the phase included in the conclusions of just about every scientific paper: further experiments are needed.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #776018 06/10/19 12:58 am
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I decided not to spare you from the dark underbelly of jetting a Concentric. Rather than draw a smooth curve the attached graph shows two day's worth of data in all its glory. By the way, those data don't plot themselves. It takes the better part of 2 hours after each run to find the one or two dozen time intervals worth examination, copy them to Photoshop, format, print, and then mark the AFRs and measure the corresponding relative throttle openings from the 0-1.55V signal from the throttle position sensor.

The first thing to note is I changed the main jet from one marked '220' that I used yesterday to one marked '200' today. This should have leaned yesterday's ~12:3:1 at full throttle to 13.5:1. Instead, the mixture became richer by the equivalent of having changed a 220 to a 225 rather than a 200. I've mentioned several times over the years that I measured a number of '500' AMAL main jets on my flow bench and found 25% of them to be as much as 3½ sizes too large or too small. The other 75% weren't perfect, having a spread of almost +/-1 jet size. Anyway, as these two jetting runs show, the '200' in it now is somewhat richer than the '220' that was in it yesterday.

I don't know if the '220' is smaller than its marked size, or the '200' is larger, but they're close enough that it makes sense to plot both sets of data on the same graph. Unfortunately, to measure the relative flow of the two jets would require me to dismantle the carburetor fixture from the flow bench, which I'm not inclined to do because I have more measurements I want to make. After plotting all the data I examined the outliers to see if I had made any mistakes, or if I had extracted any of them from graphs where I hadn't allowed the mixture to stabilize for ~4 sec. This removed three data points, but the three x's between 0.4 and 0.5 are real.

The scatter of the data points isn't due to experimental uncertainty in reading the values from the graphs, it is real. The same throttle setting under different conditions (e.g. accelerating on level road vs. climbing a hill) gives somewhat different AFR readings. Also, after yesterday's run the AFR at idle was 12.2. Today it was 11.5 even though I hadn't touched the mixture screw in the meantime.

Trying to find information on the "perfect" air/fuel ratio for gasoline, let alone E10 or E15, quickly takes one down a rabbit hole. If information is correct that 13.5:1 is the ideal ratio for maximum power then my present ~12:1 robs me of ~2%. However, if 12.5:1 is the correct ratio, my current jetting essentially robs me of nothing other than the price of having to refuel 4% more frequently if I ride all the time at full throttle. On the other hand, if much of my time is spent between 1/8 and 1/4 throttle my current jetting gives me better economy at the cost of only ~1% of the power in that range.

Just as with yesterday's '220', the performance with today's '200' felt perfect. The current configuration of the bike makes it a lot of fun to ride. At this point I'm, ahem, leaning toward calling it rich enough and removing the A/F sensor and associated apparatus. If it weren't the onset of summer I would be strongly inclined to inflict these measurements on the Catalina next. That might have to wait until Fall.

Attached Files AFR_9June19_04.jpg
Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #776049 06/10/19 1:08 pm
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Looking at the scatter of the data points, one things clear to me (in simplistic terms)...it's economical in the area of throttle openings likely to be used at sensible traffic speeds (where economy is a bonus) and will make good power at the throttle openings where power is required - big handfuls for going fast, accelerating and up hills..nice.

Looks like you have it nailed, the proof being that it's fun to ride..which I take to men that it responds readily, carburets cleanly and performs well...which is both satisfying to the tuner and rider alike.

Good effort.

KW

PS ..ad you solved problems with the mag, starter and battery charger/s that you didn't even know you had!

Last edited by Kerry W; 06/10/19 1:10 pm.

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Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #776058 06/10/19 4:58 pm
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Originally Posted by Kerry W
PS ..ad you solved problems with the mag, starter and battery charger/s that you didn't even know you had!
Yeh, sort of like setting out to simply install a new spark plug and ending up rebuilding the engine, gearbox, and both brakes before the plug is finally in place...

Luckily, I enjoy this sort of thing, but progress can be slow since I can't help digressing into making flow bench measurements, capturing 400 MHz oscilloscope traces, machining tachometer-drive timing checking tools, etc.

The only known problem that remains with this Gold Star is that its 10:1 piston isn't happy with 92 octane fuel and 100 oF temperatures. Despite using a name-brand octane booster I still heard a worrisome rattle a few times during these jetting runs so I have on order a super-expensive booster that will give me 100 octane at the equivalent cost of ~$8/gallon (I know, I know, Europeans won't be sympathetic when reading that number). "Racing fuel" is available at a few hot rod shops in town at approximately the same price, but the advantage of an additive is 8 oz. will turn a 2-gal. tank of 92 into 100 octane. Eight oz. is a small enough quantity to easily carry with me and will allow a range of ~200 miles away from the rest of the bottle back at base.

I don't know what piston is in my Catalina, but the only time I heard it rattle was when I turned onto an uphill street going too slow in a gear that was too high. Quickly grabbing the magneto lever and downshifting dealt with that. The 'Competition' isn't as easy-going.

Re: Correct needle for 1000-series Concentrics? [Re: Magnetoman] #776061 06/10/19 6:10 pm
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10:1 is certainly 'adventurous' on 92...I'd have expected not more than 9:1 and probably more like 8.5...

I know of a guy who is in the process of quantifying how much or little effect that drop in compression might have on perceived performance...

KW


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