D2B Magneto Restoration

15 September 2005 - Today I found out about some collectors in Europe getting together to do a magneto restoration project. This entails several owners going through the restoration process on their individual magnetos simultaneously. This allows the sharing of information and sources for parts as well as a helping hand if someone gets stuck. The general consensus is that most R12 owners pay a professional to overhaul their magnetos, myself included. However I have obtained a spare magneto for the purpose of going through the overhaul process myself. Dietmar Nix in Germany is spearheading this effort. As the project exists now, at the conclusion we should have a list of instructions and parts sources for anyone wanting to attempt a magneto overhaul themselves. Below is a link to Dietmar’s project page.

The magneto I am going to overhaul was incorrectly installed on a R11. However the owner found out that the R11 magneto he needed actually rotated in the opposite direction of the R12. He found the correct magneto and I got his original. The next few photos show the magneto in the condition that I received it in.

7 October 2005 - Unfortunately after I got done tearing down the whole magneto I have determined that this magneto is actually R11 or some other left rotating magneto. The point’s plate rotates left, the front gear cover is marked left, and the spark advance cable is for the left rotating point’s plate. I am now seeking a correct right rotating R12 magneto. Hopefully in better condition than this one.

The magneto is marked on the top with “BOSCH GERMANY D2B RS172”. In between the oiling caps is text which states the magneto needs to be oiled every 2000km.

This is a shot of the front showing the direction of rotation.

It appears that the left and right magnet plates (black rectangle on the side with the screw in the middle) are interchangeable from side to side. But due to the offset of the screw you could not turn them upside down. As you can see I am missing both spark plug brushes, wires and caps.

Here is a shot of the magneto bottom

The voltage regulator cover on the rear has some damage to the left side. The point’s assembly is right below the regulator. I am missing the Kontaktgebergehäuse (contactor case) that goes around the point’s assembly. This allows the rider to change the spark advance. There is a cable on the handlebar that allows the contactor case to be rotated and change the time at which the points open. Notice the “L” cast into the breaker point housing. This means this plate is for a left rotating magneto. The R12 uses a right rotating magneto.

Here is the voltage regulator exposed. The brown phenolic board on the regulator is cracked. Also due to the visible unterminated wires I can tell someone has been inside this magneto.

These two photos show the contactor cap and retaining clip. The contactor cap is a newer reproduction.

September 24 2005 – Today I disassembled the magneto. Things are not looking good. I have come to the conclusion this may become a parts donor. I have a few damaged and wrong parts in regards to making this a correct R12 magneto. Many photos follow. Here are photos of the front cover removed and cover with screws. It looks like only one of the front cover screws is the correct one. Two were to small and the two remaining screws had different heads.

Here I have removed the center gear. It had a “C” clip holding it on the gear post. The second photo shows a heavily damaged gear (missing many teeth) with the center brass insert for the gear removed.

By removing two screws the center gear post is easily removed.

Here are the magnets removed. I stored them on refrigerator for safekeeping.

This is a front and rear photo of the left rotating point’s plate.

Here is an inside photo of the rear cover showing the worn down armature brushes. Next we see the magneto rotor and generator armature ready to come out.

The generator armature seems to be in good condition. The next photo shows the mounted roof coil.

The magneto rotor has some problems. It looks like someone has been into this guy. The coil has been removed from the center of the magneto. The second photo shows what appears to be a metal capacitor inside of the end. I am wondering if you would have to remove the coil to replace this anyway.

Here are a couple of more shots of the magneto rotor. The second photo has a good shot of the two phenolic insulators (right end). The spark plug brushes ride between these on the copper strip. As you can see, one of the insulators has been cracked and repaired.

Here is a shot of the empty case and the removed roof coil. I have not removed the bearing races.

Here is a photo of the magneto disassembled down to its smallest parts (most of them anyway).

Project Stopper!

September 27 2005 – In light of the missing and damaged parts, it looks like this project has come to a halt. When I tally up the expected costs to repair this magneto, it seems to me I would be better off sinking my cash into another magneto in better condition.

I need replacements for the following parts as shown on the D2B Project website (2. Exploded view):

1. 1. 11b – brush ring on the magneto rotor. Mine is damaged – possibly useable, but I would prefer to replace.

2. 2. 11f – gear on the magneto rotor. Mine has a couple of damaged teeth.

3. 3. 16 – coupling gear – several broken teeth.

4. 4. 23 – regulator – standard replacement item.

5. 5. 32, 34, 38 – ingnition points adjuster – I am missing all of these pieces.

6. 6. 36 – points plate – I have the left rotating one, need the right.

7. 7. 40 and 39 – spark advance cable holder – I have one for the wrong side, missing the coupling screw (39).

8. 8. 27 – need new brushes.

9. 9. 11d – need new capacitor.

10. 10. 12 – need the entire sparkplug brush assembly.

11. 11. Various screws.

12. 12. bearings.

13. 13. Rewinding of magnetics.

14. 14. Capacitor.

All of this plus the fact there is a hairline crack in the top of the magneto make it tough to move forward with this one. Here are some additional photos of the incorrect, damaged parts. The roof coil has two of the wires trimmed. I don’t think this is important if you are going to a solid-state regulator.

Here is another shot of the brush ring, note how it has been broken and reglued. The second photo shows the damaged teeth on the magneto rotor gear.

Here is a photo of the left hand rotating point’s plate and the left side spark advance cable holder. Both wrong for R12.

How about the munched up coupling gear.

The moral to this story is the same that applies to buying entire motorcycles. It is really hard to tell the condition of the inside of any component whether it be an engine, transmission or magneto. With these old and hard to come by bikes and parts, it is often hard to inspect what you are getting due to the great distances between buyer and seller. So if you can’t do it don’t spend more than you are willing to throw away. In this case, I got the magneto at a very reasonable price. If it was good, I was getting a bargain. If it was bad, I was not sweating the money.

Return to main page