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Bosch DU 4 Magneto Wiring Help Sought


hddennis
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I've been trying to help a new 1917 Maxwell owner revive his grandfather's car and am having a wiring problem. This car should have a Simms magneto but his grandfather put a Bosch DU 4 on it and I'm totally out of my element. Most I find online have 4 terminals and this one has 5 with the fifth having a wire running to the  front . I found a set of pictures showing this same wire but it doesn't look like something the  factory would do. Anyone have any idea why it would be done?

 

Howard Dennis451588784_Screenshot2021-12-12195226(2)-Copy.jpg.64945c6f7d5c1ed9797f0ffe9c018239.jpg867374746_Maxwell3.jpeg.de65832a666a8dde05284ecd4b762385.jpeg

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The fifth terminal usually means that a battery can be hooked to it (with coil) so that car can run on battery (with magneto just acting as a distributor) or only on magneto.  This would be a duplex magneto and that should be marked on side where DU4 is stamped.  Easy to start on battery, then switch to magneto to run….

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11 hours ago, trimacar said:

The fifth terminal usually means that a battery can be hooked to it (with coil) so that car can run on battery (with magneto just acting as a distributor) or only on magneto.  This would be a duplex magneto and that should be marked on side where DU4 is stamped.  Easy to start on battery, then switch to magneto to run….

 

 

Dave is correct.........it made sense for stocking purposes to just sell the dual instead of the single. The DU4 is the most common and reliable magneto ever made.....it should be easy to service and find parts. There are several well known rebuilders, most are busy and weeks to months out.......

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Thanks George,

Your diagram seems to indicate a solid wire. All the ones I found seemed to be dotted lines which I'm not understanding. I also am failing to understand the 4 and 5 terminal caps.  Your pamphlet shows 4 terminals and is American  Bosch which I think was  after WWI and the 5 terminal caps like my friend has seem to be prewar.1330889372_BoschDU4Wiring2.JPG.8140f2db4f41e3ced84fb5bbb309b04c.JPG

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19 hours ago, trimacar said:

The fifth terminal usually means that a battery can be hooked to it (with coil) so that car can run on battery (with magneto just acting as a distributor) or only on magneto.  This would be a duplex magneto and that should be marked on side where DU4 is stamped.  Easy to start on battery, then switch to magneto to run….

I believe this response answered the question regarding the fifth or center terminal. Here’s a schematic.43DDF83B-6388-4AC1-9832-1F0F319A5AD3.jpeg.de37a839f9867a652a247bfe4b1e741b.jpeg

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Your schematic's have shown up on other searches I've done and they all show switches and coils that apparently my friends Maxwell wasn't equipped with so we are wondering if his solution was the wire in question simply replaced all that and allowed the magneto to be used as it's own ignition source? 

To someone who fully understands electrical systems completely this may seem to be a stupid question but we don't understand and are trying to revive this car with out burning up rare and expensive parts while doing it.

 

Howard Dennis

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I believe Roadmaster is correct. For your purposes you need that wire to the center terminal as the spark is generated on the tower at the drive end that the wire connects to.  Some have a solid center connector to the rear of the distributor gear and only have 4 terminals for the spark plugs. 

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That wire attached to the tower and running around to the other end; isn't it just replacing the part that should be there, but would be bypassing the safety gap? https://www.ebay.com/itm/164170376742

Unless there are other issues, I am not aware that that wire would even be used or needed. The 5th terminal would be used in conjunction with a standard 6 or 12 volt automotive coil, or Model T coil with bridge tied down for starting on battery.

Edited by Mark Gregush (see edit history)
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Here is the published information on the 1917. Not much compared to other years. Notice it has an additional component tied in with the magneto and may be why something is jumped or bypassed. 12 volt car......interesting. Not much published on Simms........but they are so basic that it shouldn't be any trouble.

IMG_4824.jpeg

IMG_4825.jpeg

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The 5th terminal does not have to be used, the magneto should work fine without it. Unless, the rod that goes through the magnets to the other end is missing/damaged. That rod assembly is what carries the current to the front, point end. The 5th terminal on the cap is there IF you wanted to use battery/coil to start the car, then switch to run off the magneto. The kill wire would be connected to the cap covering the points terminal. If you look at the one I posted the link to, you can see at rod looking piece.

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I'm going to try to express my concern one more time. Like Mark I fail to see why this wire is needed. Edinmass, the car in question has had the original Simms magneto replaced with a Bosch DU 4. The original Simms magneto, unlike the Bosch was NOT able to spin fast enough by the starter to generate sufficient spark. That problem was solved by an intensifying coil and dry cells until the engine caught and reached a high enough RPM for the Simms unit to take over and run the engine. Those parts of the system were long gone over half a century ago when the owners Grandfather replaced the Simms with the Bosch magneto. That intensifying coil is something I have only seen one example in over 30 years of hunting so that route is not an option. All we want to do is get this car running again in it's current configuration as his Grandfather was able to do back in the 1960's. BUT I want to fully understand how and why he was able to do this modification before I tell the new owner to hook up 2 6 volt batteries and hit the starter switch. 

 

Howard Dennis

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18 minutes ago, Mark Gregush said:

The 5th terminal does not have to be used, the magneto should work fine without it. Unless, the rod that goes through the magnets to the other end is missing/damaged. That rod assembly is what carries the current to the front, point end. The 5th terminal on the cap is there IF you wanted to use battery/coil to start the car, then switch to run off the magneto. The kill wire would be connected to the cap covering the points terminal. If you look at the one I posted the link to, you can see at rod looking piece.

Thanks Mark, you've expressed my thoughts exactly but not having enough real knowledge on the subject I came here for clarification.

Howard Dennis

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I agree you don't need that wire........here is a link that you may find helpful........if this doesn't answer all your questions, nothing will. Parts diagrams are at the bottom, and very helpful.  

 

 

https://oldcroak.com/bosch-du1-du2-du4-du6-early-pre-ww1/

Edited by edinmass (see edit history)
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2 hours ago, hddennis said:

unlike the Bosch was NOT able to spin fast enough by the starter to generate sufficient spark.

This is why many cars etc not having duel sources, using magnetos, are equipped with an impulse coupler. It is a device that has an internal spring and latch. When the spring is wound while cranking and the correct spot is arrived at, the latch releases, allowing the rotor to spin faster, generating a stronger spark.

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9 hours ago, edinmass said:

 

 

Here is the published information on the 1917. Not much compared to other years. Notice it has an additional component tied in with the magneto and may be why something is jumped or bypassed. 12 volt car......interesting. Not much published on Simms........but they are so basic that it shouldn't be any trouble.

IMG_4824.jpeg

IMG_4825.jpeg

Edinmass,

Do you have page 256 of this information? I'd like it for my files if you do.

Howard Dennis

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Yes, it’s a weird book.......I think they were going to put Simms info there, but didn’t have anything. I looked through my files and didn’t find one thing on them.

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In going back over this to decide how to explain what to do to the new owner I think I stumbled across one answer to my very first question. Mark mentioned he didn't see any reason for the wire unless the connecting rod # 14 was damaged. I went back to my first picture to illustrate what I was talking about and  noticed the rod wasn't damaged it wasn't even there! So I plan to have my new friend check first to see if his is missing as well and if not is it broken or corroded and won't pass current. 

 

Howard Dennis451588784_Screenshot2021-12-12195226(3)-Copy.jpg.64945c6f7d5c1ed9797f0ffe9c018239.jpg.c74301cc6c949392a9ae81b6397eaed8.jpg675156028_Screenshot2021-12-14194743(3).jpg.eb0033c1cf26469c758448041bc00faa.jpg

 

 

 

 

 

 

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10 hours ago, hddennis said:

I'm going to try to express my concern one more time. Like Mark I fail to see why this wire is needed. Edinmass, the car in question has had the original Simms magneto replaced with a Bosch DU 4. The original Simms magneto, unlike the Bosch was NOT able to spin fast enough by the starter to generate sufficient spark. That problem was solved by an intensifying coil and dry cells until the engine caught and reached a high enough RPM for the Simms unit to take over and run the engine. Those parts of the system were long gone over half a century ago when the owners Grandfather replaced the Simms with the Bosch magneto. That intensifying coil is something I have only seen one example in over 30 years of hunting so that route is not an option. All we want to do is get this car running again in it's current configuration as his Grandfather was able to do back in the 1960's. BUT I want to fully understand how and why he was able to do this modification before I tell the new owner to hook up 2 6 volt batteries and hit the starter switch. 

 

Howard Dennis

Not needed if the connecting bar is there but... I don't see a connecting bar.

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  • 1 month later...
  • 9 months later...
On 12/14/2021 at 10:38 AM, George K said:

I believe this response answered the question regarding the fifth or center terminal. Here’s a schematic.43DDF83B-6388-4AC1-9832-1F0F319A5AD3.jpeg.de37a839f9867a652a247bfe4b1e741b.jpeg

Hi George, Any chance you can email me a copy of this as I cant read it when I zoom in and I am looking to rewire a Hudson 33 Magneto that has been removed? This is the schematic that I have been looking for. Thanks in advance. Mathew

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  • 3 weeks later...
On 11/13/2022 at 11:36 AM, Hudson33 said:

Hi George, Any chance you can email me a copy of this as I cant read it when I zoom in and I am looking to rewire a Hudson 33 Magneto that has been removed? This is the schematic that I have been looking for. Thanks in advance. Mathew

Good Morning:

I would also appreciate a copy of this book. I am restoring a couple of 1914 Jeffery four with the Bosch DU duplex system

thanks

jose

 

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2 hours ago, Oldsoul58 said:

Hi George K. Would it be possible to get a copy of your Bosch DU4 High Tension Mag book as I am working on a 1913 Hupmobile with this mag and do not have any info on the mag. Thanks. Dale.

https://oldcroak.com/bosch-du1-du2-du4-du6-early-pre-ww1/

 

This may help...it was listed above. They are very simple. 

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On 12/14/2021 at 8:34 PM, hddennis said:

In going back over this to decide how to explain what to do to the new owner I think I stumbled across one answer to my very first question. Mark mentioned he didn't see any reason for the wire unless the connecting rod # 14 was damaged. I went back to my first picture to illustrate what I was talking about and  noticed the rod wasn't damaged it wasn't even there! So I plan to have my new friend check first to see if his is missing as well and if not is it broken or corroded and won't pass current. 

 

Howard Dennis451588784_Screenshot2021-12-12195226(3)-Copy.jpg.64945c6f7d5c1ed9797f0ffe9c018239.jpg.c74301cc6c949392a9ae81b6397eaed8.jpg675156028_Screenshot2021-12-14194743(3).jpg.eb0033c1cf26469c758448041bc00faa.jpg

 

 

 

 

 

 

I've worked on these mags in the past. One thing no one mentioned is whatever you do, do not run external power ( Coil and Battery) to the center post in the cap without without disconecting the wire that runs along side. You will burn out the internal windings in seconds. Yours does not have the spring loaded center bar because it was made to run off of a switch that would switch out the mag from Battery to Mag positions. Old hand crank tractors, trucks, and other equipment had the center bar as a battery was never intended to be in the system. The wire running along side has bypassed the proper switch and should only be used as a mag that way. If it is a good and hot mag it will start and run the car fine. You can shut the car off with the advance and retard lever. If you have a post on the point cover, That is where a ground wire will go to shut the mag off also. Do not feed external power to that lug either. Hope this helps. Also, if you do decide to run off of a battery and coil, you would will need to ground out the wire on the end that is disconnected from the rear to keep the windings from burning out. The switch basically had a "Spark Saver" that was built into it to run the windings of the mag on when the switch was in other positions. Hence, no spark saver on this paticular style of DU4 mag itself. Dandy Dave!

Edited by Dandy Dave (see edit history)
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