Bosch Mag question

[Guardian1fox2]

Got the DU4 reassembled and clean. Looks great.

Followed the original assembly instructions, but I’m not getting a spark when I spin it at the plugs or in the safety spark gap area. I’m doing it by hand with spark plug wires connected to plugs on table. In manual, with everything disconnected I still should see something in the safety gap.

The points seem way off according to the instructions. When the points are at the middle of the cam, it looks like they’re almost open 1/4” (not a good guess but to express the difference). Instructions call for .4mm. I just wanted to check with y’all I’m sure someone on here knows way more about them can give me some advice. Is the points indeed supposed to be .4mm? I also need to gap the plugs I removed from the engine when I first got it just for testing purposes. I’m running new plugs now which I’ll also have to gap to .18”. I’ll include pic here of what it looks like and my feeler gauge:

[Dropacent]

Jacob, that points set MAY have had the red fiber replaced. It was many years ago, and can’t remember my name some days. I’ll take a pic of another set here later and post. You may be able to sand and polish that down just a bit to help. Yes, gap looks way too big to me.

[speedytinc]

There is plenty of movement in the adjustable point. Undo the lock nut & close the gap. If I remember correctly the gap is .016"
Doing the math to your .4 mm equals .015748". aprox .016"

[Guardian1fox2]

There is plenty of movement in the adjustable point. Undo the lock nut & close the gap. If I remember correctly the gap is .016"
Doing the math to your .4 mm equals .015748". aprox .016"

Thank you! That’s what I’m going to do, just wanted to check!

Should I still get spark in the safety gap though? Or do the points need to be set correctly for that too?

[Wayne Sheldon]

If the "safety gap" you are referring to is the gap under that porcelain thing under the horseshoe magnets? You do not want to see a spark in there! It is a wide gap that hopefully might prevent the armature from blowing though its insulation IF the wiring or ground path somehow fails between the magneto and the engine ground. The problem is that the safety gap is wide enough that often the armature will burn through its windings in spite of the safety gap. Closing the gap down a bit might help, or it may cause misfires even under otherwise normal operating conditions.

Been a long time since I have played with a Bosch DU4. I like them. But they are tricky. Manufactured for nearly thirty years, many changes were made on them. Pieces got exchanged, timing marks varied and got mixed up. Points came in clock-wise and CCW versions, and the outer housing with the fixed cams for the points also varied. Getting all the right and compatible pieces together, lined up, and timed properly can be tricky. However, these are relatively simple magnetos. Once you get it sorted out in your head, they fall together fairly easily.

From the limited details so far, I don't have any really good suggestions about where the problem should be looked for. Points gap, cam positioning, gear timing? Everything the proper direction?
One suggestion, a good way to test the mag. Use four pieces of moderately stiff wire (copper or steel really doesn't matter) about six and eight inches long. Attach one each under each face plate distributor contact. Carefully route each over and down to near the base of the mag. Keep them all about a half inch from ANYTHING until the other end is about 1/8 inch out from the mag's base. Keeping fingers, hands, and any and all other appendages a fair distance from the "hot" end. You should be able to spin the mag by hand (may need something to grab ahold of?), and watch each wire fire off in proper order. The mag doesn't care whether the spark path is six inches or six feet, so long as it has a reasonable gap at some point.

Another diagnostic trick. Is that even at rest, the magnetic field flows through the armature. If everything is working properly? You should be able to feel the field while slowly turning the armature by hand. If a mag is really good, you should be able to "bounce" the armature between the magnetic fields.

[Guardian1fox2]

If the "safety gap" you are referring to is the gap under that porcelain thing under the horseshoe magnets? You do not want to see a spark in there! It is a wide gap that hopefully might prevent the armature from blowing though its insulation IF the wiring or ground path somehow fails between the magneto and the engine ground. The problem is that the safety gap is wide enough that often the armature will burn through its windings in spite of the safety gap. Closing the gap down a bit might help, or it may cause misfires even under otherwise normal operating conditions.

Been a long time since I have played with a Bosch DU4. I like them. But they are tricky. Manufactured for nearly thirty years, many changes were made on them. Pieces got exchanged, timing marks varied and got mixed up. Points came in clock-wise and CCW versions, and the outer housing with the fixed cams for the points also varied. Getting all the right and compatible pieces together, lined up, and timed properly can be tricky. However, these are relatively simple magnetos. Once you get it sorted out in your head, they fall together fairly easily.

From the limited details so far, I don't have any really good suggestions about where the problem should be looked for. Points gap, cam positioning, gear timing? Everything the proper direction?
One suggestion, a good way to test the mag. Use four pieces of moderately stiff wire (copper or steel really doesn't matter) about six and eight inches long. Attach one each under each face plate distributor contact. Carefully route each over and down to near the base of the mag. Keep them all about a half inch from ANYTHING until the other end is about 1/8 inch out from the mag's base. Keeping fingers, hands, and any and all other appendages a fair distance from the "hot" end. You should be able to spin the mag by hand (may need something to grab ahold of?), and watch each wire fire off in proper order. The mag doesn't care whether the spark path is six inches or six feet, so long as it has a reasonable gap at some point.

Another diagnostic trick. Is that even at rest, the magnetic field flows through the armature. If everything is working properly? You should be able to feel the field while slowly turning the armature by hand. If a mag is really good, you should be able to "bounce" the armature between the magnetic fields.

Thanks for the tips Wayne!

I was just suggesting the safety spark gap as it was a means in the manual to test for function. It said if it was installed on vehicle, to remove all wires and ground, and turn engine over briskly and you should see a spark in that area if functioning correctly. I don’t want to mess it up so definitely will avoid that!

There are no rotation arrows, but it seems that it is a clockwise setup for the Model T, with an anti clockwise points set, (since it turns opposite from the gear end). When assembling, I made sure to line up the timing marks, C for clockwise on the distributor gear with the dot on the shaft gear. I tried following the manual as close as possible. This is the manual I used: https://oldcroak.com/magneto-service-ma ... osch-1928/

And here is the pic of the timing assembly part, I basically matched the picture (on the left since that’s the point plat direction I have):

I’m at work now so I was unable to adjust before leaving. But with everything how it is now, turning the shaft and if I touch the end where ground wire goes to switch you can feel a tingle…but I’m barely turning by hand. Once I adjust points I’m gonna put a socket and long ratchet on it and spin it quickly with the plug wires and plugs connected. Unless it needs to have a ground connected then I’ll figure that out for countertop testing. I switched out the armature as the collector ring was broken on the old one, but it seemed to fit fine (not to mention a lot cleaner). Lol

[henryford2]

you are grounding the plugs "setting on the table" back to the magneto?

[Dropacent]

I just tested mine holding it, turning the shaft about a quarter turn I got I nice little jolt. If spun, I’d probably wet my diaper. I can barely see the gap in the points, so I know yours is way too wide. Picture to come yet. I know you aren’t suppose to spin them fast unless all wired up.
Wayne, I’ve only ever kept aluminum base models but have had a dozen apart at a time to clean and everything is interchangeable. I would suspect any brass base DU4 is the same. Extremely easy to change rotation, and I always tell people to disregard the arrow on the oil lid unless they check the points. Those determine rotation, and gears can be easily meshed accordingly. The only difference I can think of during production would be the big red cap and adjoining casting to take the clip mount instead of the 2 small hex bolts.

[Dropacent]

This is the points set for the side drive like yours or the cross shaft front drive eismann, matco, Columbo, others. “ C” denotes clockwise…..** note the gap, ****

[Dropacent]

This points set is for the 3 gear splitdorf aluminum front plate with mag mounted shelf on the side. NOT YOUR STYLE …… It’s marked “A” for anti clockwise or counterclockwise. Points are interchangeable, so never pass up a junker, it may be low mileage and have some good usable parts.

[Dropacent]

DISREGARD ANY STAMPED LETTER(s) ON THE front side of the points set…..the C and A are stamped on the backside where I’m pointing. Yes, it’s confusing, but you will soon be an expert, and amaze and thrill your friends and associates with a great ignition system! Let us know when you pee your pants!

[Guardian1fox2]

Thanks guys for the info. Perhaps grounding is indeed the issue “on the table”. I set the points as close as I could…my gauge wouldn’t fit…and I don’t have a small enough wrench , but I think I got it close. See here:

As you said, can’t really see the gap this is at maximum lift.

Attached a wrench to back of mag, and put wires and plugs on it on table…nothing. However, turning slowly by hand…I was brave/stupid and grabbed the grounding stud where switch would attach, and I could feel a tingle. So I guess I just need to put a wire on that to a ground…and THEN I should get something…I think lol.

It’s definitely not “easy” to turn…idk if inbetween the poles if it should basically free spin but it doesn’t. That’s also trying to spin via my fingers on a small nut on the shaft lol. Think I’m making some progress, getting close.

When I finally verify spark, I’ll make another thread with installing the bracket/gear and timing it on the motor. I also would like at that time to thank a member in that post for the generosity of building me a linkage for the spark advance it’s very very cool! Wanna have pics when I do

[Dropacent]

Ya Gotta get a wrench and feeler gauge to work. There are small ones out there just for Bosch that have a gauge attached to them, but in the meantime, just grind what you have shown above so it’ll fit( unless an heirloom piece or sumthin sumthin. Small vintage craftsman ignition wrench sets are all over the place. Good to have some to choose from and keep the best one with you, maybe on your keychain. . I have a favorite old tiny box wrench that has the perfect angle to it. I think it also fits the points plate bolt. As the red fiber wears down you should check and reset but it takes a looong time with regular light oiling. Also, there are different thickness’s of the platinum points sets. Looks like your fixed point is getting pretty thin.

[Dropacent]

As for spinning, it should turn pretty easily unless something is binding up. Sometimes a small paper gasket is needed to make clearance for the ball bearings, but should be done at that step. Kind of hard to convey what hard to turn is over the interweb,

[Dropacent]

If it’s binding here at all, perhaps the red fiber needs sanded and polished down a bit. The color of it tells me it likely has been replaced. Check that out.

[Guardian1fox2]

If it’s binding here at all, perhaps the red fiber needs sanded and polished down a bit. The color of it tells me it likely has been replaced. Check that out. 6B93DFD1-00EC-49E7-A091-3DECB69A8010.jpeg

Nah the arm isn’t binding, there’s still some room for it to move but where I show now is maximum open.

It seemed to spin better with the original armature, but perhaps it just fits a little tighter, perhaps with use it’ll free up more. It’s hard to say I’ve never handled any other ones lol. Ima take some wire tomorrow and attach to the ground stud and secure it somewhere that’s grounded in the house and try again. I’m sure I’ll get something then. After watching some YouTube videos on different magnetos I can see they throw a nice spark so it should definitely be noticeable lol.

[Dropacent]

Forgot about the new armature…. Just barely loosen up the screws on one end…….if it’s better, a thin paper gasket with do the trick.

[Dropacent]

Just thinking out loud here. I think I remember some thin paper gaskets behind the bearing race on some I’ve taken apart. I’m thinking that’s how it may have been put to the sweet spot originally. Wish other bosch affectionos would share any knowledge.

[Guardian1fox2]

When I disassembled this one, there was a fabric or something behind the race which I didn’t remove. But I thought that that was the oil wicking material to deliver oil to the bearing.


ANYWAYS! EUREKA!

I got my dad on the phone, he’s an electrical engineer, and his father was an inventor and electrical guru. I described what I had, and basically I was thinking about this all wrong. I cannot just connect the plugs to the magneto and see a spark as the body of the plug with the threads is the ground to complete circuit. So I removed the plug, and just brought the wire to the ground and VIOLA! Large spark!! Now…for my carb to finish getting rebuilt so I can check this thing out!

[Dropacent]

Great on you for following through on it , Jason! Treasure those phone calls to dad, as I sure miss my conversations with mine. He was my go-to guy for so many things, and I still have his little schematics here to help me, being the dim witted son.
Love to see a younger guy making his T special, keep at it!

[Guardian1fox2]

https://youtube.com/shorts/1rEUX2nMR8o?feature=share


For your enjoyment lol I was testing it, I got the spark then got confident. My son was distracting me and I guess my hand got a little too close to the end hahahaha

[Guardian1fox2]

Great on you for following through on it , Jason! Treasure those phone calls to dad, as I sure miss my conversations with mine. He was my go-to guy for so many things, and I still have his little schematics here to help me, being the dim witted son.
Love to see a younger guy making his T special, keep at it!

Thanks!! My 5 year old just got the laugh of his life when I shocked myself lol

[Michael Peternell]

You know it's a good one when the jolt hits your shoulder! Sometimes when you get one at the fleemarket you can't help but giving a twist to it to feel for the magnets. Got my attention more than once! Made me feel really good about my purchase! After buyer shock wore off.