Restoration of a Bosch ZEV magneto

[BoschZEV]

Some of you might be interested in the detailed description of the restoration of a magneto I posted to BritBike Forum under the name Magnetoman. It is the most extensive such description I am aware of on the web or in print, requiring 20 posts over four months to complete. The subject of the thread is a Bosch ZEV I restored for a friend's 1923 Harley-Davidson that he subsequently rode in the 2012 Cannonball Rally:

http://www.britbike.com/forums/ubbth...46733#Post4467 33

My obsession with magnetos was, ahem, sparked in the mid-1990s when I restored a BSA Gold Star that came with a nonfunctioning magneto. Rather than taking the time to figure out how to fix the magneto myself, I decided to send it to a specialist. That was a mistake. Although the specialist came highly recommended, had a very well equipped shop, and seemed quite sure of his abilities when I spoke with him, the magneto failed after 90 miles with what I recognized as a bad replacement condenser.

Anyway, as a result of that unfortunate experience with a highly recommended magneto rebuilder, and as I wrote in the 'Epilog' to that thread, "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." I should add that this is not an advertisement for restoring magnetos since I only do that for myself (and a few close friends who managed to corner me)

[marsh1915hd]

I started buying Bosch ZEV magneto's in the early 90's also but i am in no way as good as you are.
So how much did this job cost? Just to do the work I would say $1,000.
I too send magneto's to the best guy around, and had a lot of problems with the mag and it cost some miles on the Canon Ball 2010.
So you want to be the ZEV guy? I have a couple of doz. that need done? Most of the clean up work is done. Threads taped, screws cleaned up, and many other hours of works done to them.
I use to buy them for $100, now there $500 and don't work. There are fake ones, cost $1,000.
Thanks you for posting this, it is very good and i have learned a lot.
Terry Marsh

[BoschZEV]

So how much did this job cost? Just to do the work I would say $1,000.

Well, I did it for a friend, so it was priceless. I didn't keep track of the time involved, but the work I had to do to make that magneto function as good as when new easily would have cost over $1000.

I too send magneto's to the best guy around, and had a lot of problems with the mag and it cost some miles on the Canon Ball 2010.

I have to wonder how you can call someone "the best guy around" when you say his magnetos failed you. If you had someone do mechanical work on your engine and it failed, I doubt if you would say that mechanic was "the best guy," so why do people -- not just you, but a lot of motorcyclists -- accept magnetos that fail? There is simply no reason a properly rebuilt magneto should fail.

Thanks you for posting this, it is very good and i have learned a lot.

Thanks very much for the nice comment.

[marsh1915hd]

The best guy around magneto was tested for three days just could not handle the heat. Condensers were all bad, it was not just my magnetos.
By the time I have them cleaned up and working I have more in them than they will pay for one. No one wants to buy one for $1,200. They want a $500 one that cost $1,000 to repair. So I have not repaired anymore.

[BoschZEV]

They want a $500 one that cost $1,000 to repair. So I have not repaired anymore.

Yes, that's quite a problem. A magneto cannot be properly repaired for the $250 that people already think is too much. I would have lots of customers if I spent $1500 worth of my time rebuilding magnetos, as long as I only billed them $200 for the labor. However, if I billed what it actually costs, there would be very few customers lining up. So, I do what any rational person would do who has assembled a comprehensive set of instrumentation and facilities and actually knows how to diagnose and repair magnetos properly -- I repair them for free... (but only for a few friends ).

[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

[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

[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.

[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]

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.

[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]

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.

[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.

[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.

[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.