Restoration of a Bosch ZEV magneto

[BoschZEV]

Questions- is that the cap, the silver area between the brass? Do I remove the rivets and pull off the brass to expose the original caps? And then fit the new caps in that space?

The entire assembly in your photos is the capacitor. A large number of thick mica plates are separated by very thin metal "plates," alternate ones electrically connected to one brass piece and the other set of alternate ones to the other. One brass piece (and half the metal plates) is connected to the threaded stub so you'll need to recycle that stub by connecting one electrode of the modern, replacement capacitor to it. The other electrode of the modern capacitor goes to the appropriate wire of the coil.

I hope the above is clear. I'm unbelievably jet-lagged at the moment so I wouldn't be surprised if I re-read it tomorrow and say "huh?" to my instructions. if it's not clear don't hesitate to say so.

[Shaky Jake]

Well, it took me a bit to get back. I made up this puller adapter to remove the inner bearing races, when the split washer is installed, and the slip ring when they are removed. I used a 2 jaw puller to remove the parts from the shaft.[ATTACH=CONFIG]19277[/ATTACH][ATTACH=CONFIG]19278[/ATTACH][ATTACH=CONFIG]19279[/ATTACH][ATTACH=CONFIG]19280[/ATTACH]

Nice job!

Kevin
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[DanM]

Then I got the end cap off the armature assembly, and removed the part containing the capacitor. Now to remove the cap and replace with my Vishay caps. Questions- is that the cap, the silver area between the brass? Do I remove the rivets and pull off the brass to expose the original caps? And then fit the new caps in that space? I assume I need to retain as much material as possible and the stub that goes through the end cap and takes the screw for the points mechanism. Thanks again for all your support!
P1060390.jpgP1060391.jpgP1060392.jpgP1060393.jpgP1060394.jpg

[DanM]

Well, it took me a bit to get back. I made up this puller adapter to remove the inner bearing races, when the split washer is installed, and the slip ring when they are removed. I used a 2 jaw puller to remove the parts from the shaft.P1060395.jpgP1060397.jpgP1060398.jpgP1060399.jpg

[BoschZEV]

have an open condition from both A and B to the slip ring. Between A and B I have .6 ohm.

If I understand your labeling correctly, A and B are on opposite sides of the condenser. If so, and if the condenser is good, the reading should be ~0.6 Ohms because you're making the measurement between the lead that comes from the coil and the housing, i.e. through the primary coil. So ~0.6 Ohms is what it should be.

It is not clear to me the winding connections and whether I should have resistance between A or B and the slip ring. I assume so.
Can you advise?

One side of the condenser is connected to the housing, while the other side connects through the primary back to the housing (~0.6 Ohms) as well as through the primary and the secondary to the slip ring (i.e. it's ~0.6 Ohms + ~4 KOhms = ~4 kOhms because the 0.6 Ohms is a negligible addition to the total resistance unless you're using a 6-digit ohmmeter).

I also ask for clarification regarding removal of the end cap. Looks like I should un-solder the wires from the end cap connections prior to removing the end cap?

Yes, you have to un-solder the lead the connects the condenser to the coil. It's OK to unsolder the other lead as well.

How is the winding connected to the slip ring? If I were to pull the slip ring, will I find the wire soldered?

This wire is not soldered. The wire exiting the secondary is a slip fit in the slip ring. Since it will be at several kV when the coil "fires" the small gap is inconsequential. However, depending on how the wire is in that hole it may or may not be physically touching the metal of the slip ring (or it may be oxidized) so even with a good coil you still could get an infinite reading between the coil lead attached to the condenser and the outer surface of the slip ring. Once you remove the slip ring the wire will be exposed and you can make the necessary measurements. Once you have the end cap and the slip ring removed, and the coil is free standing, the resistance between the two wires at the condenser end of the coil will be ~0.6 Ohms, and between either of them and the exposed wire at the other end will be several kOhms.

Just to be clear, I've written 0.6 Ohms above but it might be anywhere within a factor of two of that depending on how Bosch made it back in the Dark Ages. Similarly, anything in the range ~3-8 kOhms is probably fine. However, coils that pass DC ohmmeter tests can still fail dynamic tests so your measurements can still give false positives for coils that will fail in operation.

[DanM]

Dear Mr. BoschZEV:

I am working on my first mag, a Bosch ZE1. ZE1 Armature A.jpgZE1 Armature B.jpg
I really appreciate your articles as guidance to the process of investigation and remediation.
My question is on measuring the coil in the armature. I have used an ohm meter between the solder joints in the capacitor end cap and the slip ring and have an open condition from both A and B to the slip ring. Between A and B I have .6 ohm.
It is not clear to me the winding connections and whether I should have resistance between A or B and the slip ring. I assume so.
Can you advise?
I also ask for clarification regarding removal of the end cap. Looks like I should un-solder the wires from the end cap connections prior to removing the end cap?
How is the winding connected to the slip ring? If I were to pull the slip ring, will I find the wire soldered?
Thanks in advance for your valuable time.
Dan

[BoschZEV]

...the technical information presented about the ZEV is unmatched!

Thanks very much for the kind words. I always like to hear when my efforts have helped someone with their magneto, although I do know the information is of interest from the number of views this thread gets. Thanks again.

[whp]

BoschZEV.

From knowing nothing about Magnetos to buying a ZEV for my J and taking it apart to diagnose condition I must thank you on your write up! I'm sure you've heard it a thousand times but the technical information presented about the ZEV is unmatched! I've probably spent about 10 hours pouring over every detail of my magneto in order to bring it into proper working order. I did run into a little trouble with how the brass insert where the earth brush rides comes out of the plate. After some... mistakes were made... I realized that it is threaded in after the fact. The oiler on the plate has a brass piece that acts as a stake to keep everything aligned and I did not know this when trying to take the piece out. The reason for disassembly was the earth plate was pulling away from the aluminum plate, and was wearing on the earth brush quite bad. I did manage to wrangle to back in correctly and is now in working condition!

I didn't quite understand the importance of re-magnetization until I had it done, I used to turn my armature about to do points adjustments decently fast and now I shock the sense right out of me.

I'd like to find the proper equipment such as your testers, I quite like this stuff but it's real tough to acquire!

[BoschZEV]

) the Dixie rotor does seem to have a bit of a dynamic imbalance. See the attached video.

Well, that video certainly explains your screen name. Either you had way too much coffee before making the video, or that magneto is a candidate for balancing. Just doing a simple static balance on a good set of rollers should make a big improvement, although the asymmetry means there will be a rocking couple that only could be dealt with by a dynamic balance. Still, that secondary source of vibration should be considerably less than the primary.

[Shaky Jake]

Instead of spinning a coil of wire in a stationary magnetic field the Dixie basically spins the magnetic field in a stationary coil of wire. I don't have one to measure but I believe the rotating part of a Dixie is heavier than the rotating armature of a Bosch. Irrespective of its total weight, since that rotating part is asymmetric it is more likely not to be perfectly balanced. That will result in vibration which will be hard on the bearings. However, it would be straightforward to balance the armature to eliminate this as a problem. Other than that one issue to pay attention to, there's no reason a Dixie shouldn't be as reliable as a Bosch ZEV.

Based on my precise scientific method and ultra-sensitive measuring and test equipment (a.k.a. my fingers) the Dixie rotor does seem to have a bit of a dynamic imbalance. See the attached video. Of course, as long as the bearings and their support structure are designed to handle the resulting loads, this doesn't necessarily result in a reliability issue.






Kevin


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[MMasa]

Eric
The Dixie design has some advantages over the Bosch design as well. These have to do with the advance/retard function.
In a magneto, there is an optimal moment for the points to open for maximum spark. This occurs at the time when the stator and armature poles are breaking their magnetic relation to each other and the magnetic field is about to collapse.
When you advance or retard a Bosch magneto, you are causing the points to open slightly before or after this optimal moment.
The Dixie is designed in a way that this pole relationship remains fixed as the magneto is advanced or retarded. The "guts" of the magneto actually rotate inside of the shell of the unit to effect the timing.
It seems to me that the weak link on a Dixie is the pot metal base.
Mark

[BoschZEV]

I'm a bit surprised that American magneto manufacturers didn't just rip-off the Bosch design during WW1;

Basically they did. Without taking time to remind myself of the details, the U.S. government seized the assets at the start of WWI and sold them to American insiders for pennies. Slowly over the 20 years after the war ended the German company bought back the assets, only to have them seized again when WWII started

[exeric]

Thanks, BoschZEV. I'm a bit surprised that American magneto manufacturers didn't just rip-off the Bosch design during WW1; but I guess everyone saw the handwriting on the wall that generators, circuit breakers, and distributors would be the coming thing, and magnetos would be taking a back seat. Most every motorcycle magneto I've looked at, looks very well built, with precision made parts, and beautifully finished. But, I guess Bosch was the cream that rose to the top.

[BoschZEV]

are there inherent design problems with a Dixie, compared to a Bosch?

Instead of spinning a coil of wire in a stationary magnetic field the Dixie basically spins the magnetic field in a stationary coil of wire. I don't have one to measure but I believe the rotating part of a Dixie is heavier than the rotating armature of a Bosch. Irrespective of its total weight, since that rotating part is asymmetric it is more likely not to be perfectly balanced. That will result in vibration which will be hard on the bearings. However, it would be straightforward to balance the armature to eliminate this as a problem. Other than that one issue to pay attention to, there's no reason a Dixie shouldn't be as reliable as a Bosch ZEV.

[exeric]

BoschZEV; can a Dixie be (reasonably) rebuilt into a trustworthy magneto? I guess what I'm asking is; are there inherent design problems with a Dixie, compared to a Bosch?