MTFCA Forum

I want to install a Bosch magneto and have acquired the mounting bracket below. Are all Bosch DU4s the same or am I looking for something specific? Any help would be appreciated.

They’re basically the same except the base is cast brass on early DU 4s and cast aluminum on later mags. I think both will fit.

Do yourself the favor of either buying one that's been rebuilt, or having one rebuilt. Rewound armatures, new condensers and freshly charged magnets make all the difference. Even with one that is original and works great, you still run the risk of throwing off the old armature windings and having the mag seize up.

Make sure the rotation is correct. They come in clockwise and counter clockwise rotations. There should be an arrow on the oiler on top of the housing. Looking from the front when mounted, it would be a clockwise rotation, the arrow pointing to the engine, turning the same direction as the crankshaft gear/engine.

You cannot rely on the oiler arrow, as all units are easily changed rotation. The points set is held by a long hex nut, change that , reset the brass gears and rotation is changed.

if you do change the rotation of the armature you also have to change the points out with the correct set, for that rotation. they made the points in both c.w. and c.c.w. rotation.
Harold III

oops, I guess I should have read the post that Dropacent posted more carefully, it does tell you to change the points. my bad.
Harold III

Tim, shown is the right point sets inside the mag. That set is clockwise. Shown on the backside , one is marked “C” for clockwise. The other “A” denoting Anti-clockwise. That is how Bosch referred to them. If you need a copy of the manual, let me know and I can email it to you. It answers everything you need to know to set it up correctly.
From memory, the 3 gear side drive setup uses an Anti-clockwise mag. The side drive like you show, and all the front mag drives use the Clockwise mag. If not correct, hopefully someone will shout out. If you don’t fool with these all the time, the info leaks from my brain. The recent Bosch mag shelf that I made up, I’m not sure of rotation required. Need to map it out someday.

“A” means anti-clockwise , also counterclockwise. “C” means clockwise

Clockwise from the drive end, correct?

If the crankshaft turns clockwise looking at the front then the camshaft turns opposite which would drive the mag anti clockwise. Referring to Tim’s new mag plate and belt driving it. Correct, maybe??

The part that always confused me is if it's CW FACING the gear on the front of the mag, or CW as if you were facing the back of the mag (like sitting on top of the mag if you were a gnome)... It's not the first time I've tried to suss this out and yet it still perplexes me... Is it facing the gear, or facing the back of the mag? ARRGHHH!!!!

On a direct drive (like yours) or one of those cool left-side chain (or belt) drive pedestal mounts, the mag will turn the same direction as the crankshaft (opposite the direction of the cam gear). On (most) crossdrives, it's the opposite.

Crank shaft from the front, clockwise, camshaft counter clockwise, generator or in this case single gear driven mag drive would be clockwise. Direction would be at the gear or driven end, so looking at that end of the magneto.
Thanks for the information on the markings. That makes it easy to swap them over if needed.

Yes, Clockwise or anti-clockwise when looking at the drive end.
Tim, those pics are gold for many people! May I steal them for my magneto records? Serious question. I don't know if I've seen that before!
Which manual do you have? Very curious. PM me if you feel it more comfortable.
oldcroak has graciously provided me with many magneto manuals. A God-send.
For impulse coupler users, most times that part's cake as the parts are marked like those "jewel pics" of the points plate.
Just flip the parts (and the spring) around so you see the A or the C/AC as your needs dictate.
Replace the interrupter (points) plate, re-time the gears and set the impulse coupler.
Susanne, I sure get ya there! In the driver's seat verses standing at the front. I've struggled with that also.
Mags are viewed with the mag in your hand or on the bench and the drive end or impulse coupler facing you.
In time, I'll need an anti-clockwise DU-4 for an OT project.
Gosh, I need to read this whole thread again! That's a good thing.
I'm more of a ZR-4 kind of guy (they are OK for a T also) and the chance to know a DU-4 is coming.

Danny and Susanne, it’s easy to get too tied up in terminology. Especially when one persons clockwise is anothers counterclockwise. Especially when one persons front of the magneto is another persons backside of the magneto. See where I’m going?
To make it easy, the cross drive front mount OR the side unit Tim Rogers posted pictures of, take clockwise points. Picture shown below, and stamped C on the backside. ( is it called a clockwise magneto ? I DUNNO) The 3 gear side drive unit takes a counter(anti)clockwise points stamped A on the backside. This for DU4 units. These units are great because they are so sturdy, bulletproof, easily changed in rotation , and timed just by moving the brass gear teeth. IGNORE THE ARROWS ON THE OILER LIDS !!
You are on your own if you want to use a Dixie, eismann Apollo, Splitdorf or one of many others. K.I.S.S.

I’ll post the manual for the DU4 here, Duey. Feel free to pass any of it on, but please let me know if I’m incorrect.

A mag that runs directly off the camshaft gear -- as most do -- will be clockwise, as the cam gear turns counter clockwise.
A mag that runs off an intermediate gear -- such as the Bosch side drive -- will turn the same direction as the camshaft; counter clockwise.

It is easy to forget that the cam gear is turning in the opposite direction of the crankshaft.

And if belt driven off the camshaft will need to be counterclockwise

I appreciate all the info, thanks! I'm in the market for a restored or fully functional clockwise DU4, let me know what you have...

I posted Dixie, splitdorf and New York coil manuals here months ago.

Who is the fellow that rebuilds these?

Depending on location here is a list on Smokstack some might be closer then others. While it does contain listings for different repairs, there are magneto repair people listed.
https://www.enginads.com/bizcards.shtml

Jerry has good advice above. This is what works for me. These Bosch DU4 mags are so plentiful ,that I only buy really nice looking ones. I take them apart, clean very well, especially the hardened old oil. I lubricate them, reassemble , and have never yet had one fail or not perform well. Knock on wood ! Another bonus is you really get to know the mechanics of your choice of ignition. I have them on 4 ts Be prepared to spend $4-600 for getting one rebuilt by a pro. I’ll let someone that has paid to have one rebuilt recommend a rebuilder.

My thoughts are recharging the magnets.

I always "sit up straight and pay close attention" whenever Bosch DU4 is mentioned. I want to thank all of you who contributed useful information to this thread, especially Tim Morsher for generously sharing the Bosch DU4 manual.

I will be saving all of this technical information for the time when the magneto on my '14 Metz causes disappointment and head scratching.

I like threads like this. Bill, I'm glad you find this useful! The mere mention of American Bosch mags perks my ears too!
Barring my own "tries" at sharing information with what little I know about these contraptions, stay clear of the wax smoke if you replace the condenser on the "rear" end of the armature with a capacitor. It smells really, really bad and never use sandpaper on the distributer.
Tim R, let us know when you find your magneto. Ya started a good thing here!
Tim M, that is the exact manual I have, jumbled pages and all! Thank you much!

Danny, is Cross lake Township in Maine close to you for recharging your magnets?
I'll admit I've not done business but thought I'd share about Mainely Magnetos there. There are many others also. Done business with some closer to me.
Funny how the antique automobile and old tractor worlds come together. Here there are 4 AB mags in care and upkeep.

Duey
I’m outside of Cincinnati but can ship anywhere. At the local museum hangout a fellow is big time into prewar fire trucks. He passed a phone number to me of a fellow he uses. I’m in no hurry, I have 2 builds I need to get finished before adding anything else.