Restoration of a Bosch ZEV magneto

[BoschZEV]

I am amazed any of our machines run. I have no idea what condition my mag's are in, however they have run dependable so far ...

Your experience is a testament to the fundamental reliability of these devices. However, some of them are nearly a century old so it shouldn't be surprising they need refurbishing. The unfortunate thing is that not everyone doing the refurbishing has been doing the reputation of these devices any favors.

[Tom Lovejoy]

One other thing this made me think about, doe's anyone have any experience with the new Magneto's being advertised in the AMCA mag?

[Tom Lovejoy]

Very interesting reading and as been said - thanks for your efforts and sharing this info. I am amazed any of our machines run. I have no idea what condition my mag's are in, however they have run dependable so far - knock on wood :-) Your site and the info on it are very good reading + appreciated by any and all who ride old vehicles with a magneto, thanks again.

[BoschZEV]

Unfortunately, the Panasonic condensers I tested so extensively for use in rotating armature magnetos are now out of production and no longer easily available:

http://www.britbike.com/forums/ubbth...734#Post467734

However, I have just completed a series of tests on an alternative that is currently in production and available at $2.70 for the pair needed for a magneto. As described in the link below, I did an accelerated lifetime test to the equivalent of 20+ years of storage at 72 oF plus 30,000 miles of use at a very high operating temperature. Details are at:

http://www.britbike.com/forums/ubbth...762#Post508762

Note that I have no financial stake whatever in these capacitors so I have nothing to gain whether or not you follow my recommendation. Also, it is worth emphasizing that the 20 years plus 30,000 miles is only a lower limit because, other than discoloration of the white plastic base, these capacitors showed no sign whatever of degradation when I ended the test after a month. There is no reason to expect they would not continue to last quite a bit longer.

[BoschZEV]

While waiting for results of my capacitor tests, if you go to the following link you will find a new post I just uploaded diagnosing in detail the cause of the failure of an aftermarket slip ring:

http://www.britbike.com/forums/ubbth...338#Post507338

As I write there, although the results of that dissection and analysis apply only to that one specific slip ring, the implications for users of aftermarket electrical components are much broader. With most mechanical components on a motorcycle it's clear whether or not an aftermarket product works. Either the holes line up properly (or the bolt has the right pitch, or the fuel tank fits, or...), or they don't. There can be exceptions, like a badly heat-treated camshaft, but largely the average mechanic can tell when they install an aftermarket product whether it has the quality they expected.

Aftermarket electrical products are a different story, since they require specialized instruments to know whether claims about them are valid or not. This can be seen in the above post about slip rings. Without a particular highly specialized General Radio Megohm Bridge that measures to 1000 TOhm (a thousand, million, million ohms) I couldn't have made some of the measurements I made that were necessary to determine the cause of failure of that slip ring. As I say at the end of that post, the failure mode of this slip ring now has me investigating other ways for stress-testing slip rings that could be used by people who don't have the necessary specialized electrical test instruments.

[BoschZEV]

Thanks to Pete and Eric for the nice comments. Unfortunately, a few weeks into my test the hot plate lost control and heated the capacitors to nearly 200 oC sometime between checks of the temperature I did every few days, causing me to have to throw out those capacitors (the manufacturer rates them to 105 oC). However, I'm happy this happened a few weeks into a month-long test instead of many months into a years-long test. Because of that I had to start again (with a different hot plate), so the capacitors won't have accumulated the necessary number of hours in 102 oC 30W Castrol until later this week.

So far everything is good from measurements I've made along the way, although a more comprehensive set of measurements using different instruments will be needed to know for sure. I hope to have those measurements done and the results ready to post in another week.

[exeric]

BoschZEV, I too would like to thank you for doing the research, and sacrificing your time, and efforts to help the old bike hobby. I have 2 ZEVs that may benefit from your work. . . And, of course; me.

[pete @ occhiolungo]

new replacement capacitors / condensers

That is great news. I can hardly wait to hear about the testing of these new caps. It is a shame that the Panasonic part number is discontinued, but hopefully whatever parts you test (and hopefully pass the tests!) will remain in production for a while.

best regards,
Pete Young

Thank you very much for the compliment. Just doing my part to keep our old bikes polluting the air... er, I mean, purring like they should.

Although the Panasonic condenser I recommend in that article is now out of production, I have a stock of them that will last me well into the 22nd century. Because of this I haven't been strongly motivated to do the work necessary to find an alternative to recommend. However, prodded by someone who did the mind-numbing job of combing through the specification sheets of available capacitors to narrow down the possibilities, I finally gave in a week ago.

Basically, an appropriate capacitor has to satisfy three criteria: have the proper electrical specifications, be of a size that fits into the cavity, and not dissolve in oil. I selected several that met the first criterion, possibily met the second, and would have to be tested to see if they met the third. Although one is back ordered and won't be shipped until early September, the others arrived a few days ago. The construction of magnetos, and the size of appropriate capacitors, are such that every fraction of a mm counts, and there isn't a way to be sure whether or not a capacitor will fit from the published dimensions. Anyway, two of the ones I ordered are just a teensy bit too fat so had to be rejected. However, the ones that fit nicely into the armature and have the necessary electrical specifications were dropped into a container of 100 oC 30W Castrol earlier today. I won't be able to test them periodically over a span of two years like I did with the Panasonics (unless everyone wants to wait that long for an answer), but if they survive for a month in oil at 100 oC without degradation, that means they would last for 2^8 x 1 mo. = ~20 years at 20 oC.

Stay tuned for an update in a month or so. Meanwhile, cross your fingers and hope they don't dissolve.

[BoschZEV]

One of the best articles on the subject! Thank you!
I now might find the cause of the failure of my professionally rebuild ZEV when hot...

Thank you very much for the compliment. Just doing my part to keep our old bikes polluting the air... er, I mean, purring like they should.

Although the Panasonic condenser I recommend in that article is now out of production, I have a stock of them that will last me well into the 22nd century. Because of this I haven't been strongly motivated to do the work necessary to find an alternative to recommend. However, prodded by someone who did the mind-numbing job of combing through the specification sheets of available capacitors to narrow down the possibilities, I finally gave in a week ago.

Basically, an appropriate capacitor has to satisfy three criteria: have the proper electrical specifications, be of a size that fits into the cavity, and not dissolve in oil. I selected several that met the first criterion, possibily met the second, and would have to be tested to see if they met the third. Although one is back ordered and won't be shipped until early September, the others arrived a few days ago. The construction of magnetos, and the size of appropriate capacitors, are such that every fraction of a mm counts, and there isn't a way to be sure whether or not a capacitor will fit from the published dimensions. Anyway, two of the ones I ordered are just a teensy bit too fat so had to be rejected. However, the ones that fit nicely into the armature and have the necessary electrical specifications were dropped into a container of 100 oC 30W Castrol earlier today. I won't be able to test them periodically over a span of two years like I did with the Panasonics (unless everyone wants to wait that long for an answer), but if they survive for a month in oil at 100 oC without degradation, that means they would last for 2^8 x 1 mo. = ~20 years at 20 oC.

Stay tuned for an update in a month or so. Meanwhile, cross your fingers and hope they don't dissolve.

[pravg]

ZEV professionally restored...

One of the best articles on the subject! Thank you!
I now might find the cause of the failure of my professionally rebuild ZEV when hot...

[BoschZEV]

These are intended for Lucas mags,I don't know if they could be adapted for Bosch.
I'm all for doing a proper job on a repair,but if even good quality condensors are prone to give out in extreme heat,these would provide a roadside fix.

Sorry, but I have to disagree. For the technical reasons I give in my thread on Britbike Forum, I definitely do not recommend using those condensers. Also, a proper replacement condenser would still be fine after crossiing the Arabian Penninsula in August. The rider will expire long before the condenser does. The condenser I recommend in that thread is rated by the manufacturer for full performance up to 85 oC, and then up to 105 oC at derated voltage. If the inside of your magneto is at 85 oC, your fuel tank is on fire. If your replacement condenser goes bad when it is warm, the rebuilder used the wrong replacement condenser.

[Limey_Dave]

These are intended for Lucas mags,I don't know if they could be adapted for Bosch.
I'm all for doing a proper job on a repair,but if even good quality condensors are prone to give out in extreme heat,these would provide a roadside fix.

http://www.brightsparkmagnetos.com/index.htm

[BoschZEV]

PS... my mention of Mark was not to take away from Bosch ZEV... But to support his point that good work costs.

I have no experience myself with him, but I do know he was the subject of much discussion during and after Cannonball 2010. However, I work on magnetos only out of interest (or, more accurately, obsession), and only for myself, so I'm not in competition with anyone who does it as a business.

[sirhrmechanic]

PS... my mention of Mark was not to take away from Bosch ZEV... But to support his point that good work costs.

We need more good Mag guys out there. And should be glad when anyone skilled in their repair comes across our radar!

Thanks ZEV!

Cheers,

Sirhr

[sirhrmechanic]

We have a lot of magnetos repaired for the shop. We do the dynamos and starters ourselves. But mags are an art. Other than some work with points, we send them out and are glad to have others who are experts. Last couple of years, I think we had about 40 mags done.

Best guy we have found is Mark's Magneto Service in Ct. He has done some bike mags for me personally... but also a lot of Ghost, Phantom and Vintage Bentley mags. And these are for cars that are driven a lot. Not trailer queens.

Mags run a LOT to restore right, especially if you have to rewind them. The prices of $1000 are not out of line. If lucky, they don't need rewinding.

The main things to consider are a: A properly done job lasts for decades. b. You will pay for a properly done job. c. You will have to wait for a properly done job. d. If you get a cheap job, you may get it fast and cheap. You won't get it right.

Buy once, cry once. The quality remains long after the price is forgotten. There is no free lunch. Choose your plattitude du Jour. But when it comes to Mags, find good people. Pay them well. Be nice to them. And you will get a mag that will outlast (probably) you. Cheap out and you'll just have to do it again. And pay for a flatbed.

Cheers,

Sirhr