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Magnetos, Ignition Coils and Spark Plugs Discussion about magnetos, buzz coils, spark plugs, ignitors and low tension coils.

Magnetos, Ignition Coils and Spark Plugs

Bosch DU4/2


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  #1  
Old 05-30-2019, 07:41:44 AM
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Default Bosch DU4/2

Hello, I have a new to me Rumely X25-40 with a Bosch DU4/2 magneto that has a deteriorating bearing or bearings. This likely is due to the mag being under a bolted on cover & does not get oiled very often.
My question is, if the armature is damaged will an armature from a DU4 fit & work? I have several DU4 mags. Or can a DU4 be converted to a DU4/2?
Thank you,
Jack
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Old 06-01-2019, 12:02:21 PM
Eric B. Eric B. is offline
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Default Re: Bosch DU4/2

I believe they are armatures are interchangeable.
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Old 06-02-2019, 10:47:46 AM
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Default Re: Bosch DU4/2

Thank you Eric, so if I change the cap assembly & interrupter housing I can make my rebuilt DU4 work as a DU4/2 ??

Jack
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Old 06-02-2019, 12:30:34 PM
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Default Re: Bosch DU4/2

You only have to change the cap and make sure the unused terminals are grounded.
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Old 06-02-2019, 07:00:36 PM
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Default Re: Bosch DU4/2

Thank you for the information. I have made a bit of a commitment to repair the DU 4/2, the new bearings arrive tomorrow. If it does not work well I will convert the known DU4 that I have. I also made some tools to do the job. (not the mag wrench)
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Old 06-03-2019, 11:11:48 AM
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Default Re: Bosch DU4/2

Like posted above armature should be the same. The only difference iv ran into is with the front pickup being different but I think that is mostly on older du4's.

I recently installed some new bearings and I was always told to use phone book cover paper as the insulator shims. On this particular mag I ended up having to take a race back out to install a different piece of paper for the face paper because the bearings were too tight when I installed the rear cover.


Chris
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Old 06-03-2019, 06:52:54 PM
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Default Re: Bosch DU4/2

Thank you Chris. I installed the new bearings today & assembled the magneto. It seems someone in the past did not understand the concept of the shims & shimmed the drive end race with brass. That was the bearing that was worn considerably. I found that file folder paper is .010" thick & of good quality. It worked well & the bearings are now isolated electrically. Perhaps I will try it on the Rumely tomorrow.

Jack
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