Details to change commando starter to four brushes

Could anyone tell me if you can use four brushes without adding two new coils.

Yes I've converted my starter to four brush. RGM does the kit.

The four brush conversion is not worth the money. £70 plus, for very little improvement in performance, and it still does nothing to stop the rotor wearing into the drive end plate and shorting out the windings. The prestolite motor as fitted to the Commando had a few built in faults, The worse fault was the bush bearings fitted, allowing the rotor to wear into the drive plate snout. Much better is to fit a 6203 2RS bearing into the drive end, controls the end thrust so no rotor wearing and liberates more motor power to start the engine. The bush bearings sap motor power.The photos show what to look for and where the rotor windings contact the drive end plate.


These show the 6203 bearing fitted into the drive end plate.


Note that the motor frame in the photos had been fitted with the four pole field coil conversion, This increased the rotor wearing problem and made it worse!
PM me if you want a copy of the starter motor overhaul notes that cover overhauling and up grading the prestolite to better than new performance, so much so that a bearing modified two pole, two brush prestolite will turn the engine over like a jap bike.

You need the 4 brush 4 coil harley prestolite stator. Agree the roller bearing modification will help also but you need a machine shop to do it.

baldy said:

You need the 4 brush 4 coil harley prestolite stator. Agree the roller bearing modification will help also but you need a machine shop to do it.

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The bearing conversion improves the motor far better than the four pole frame and getting it done corrects all the other built in faults that the original prestolite has (this was the 1970s remember, their quality control was non existant)

I did mine years ago and I've just checked it and there's no evidence of the armature having ouched the endplate. I don't have a lathe or know anyone that has so I can't fit that bearing so things will have to stay as they are. According to the parts book there should be a shim in there which I don't have either.

Of all the prestolites i have overhauled for people, more than 50% displayed the rotor wearing fault. The thin shim and spring washer (that lives between the commutator and the brush end cap) exacerbates this as they help push the rotor towards the drive end.

dobba99 said:

Of all the prestolites i have overhauled for people, more than 50% displayed the rotor wearing fault. The thin shim and spring washer (that lives between the commutator and the brush end cap) exacerbates this as they help push the rotor towards the drive end.

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Peter, just an idea, but would you be able to do the bearing conversion on an exchange basis? ( I don’t have a MkIII, but just asking).

cliffa said:

Peter, just an idea, but would you be able to do the bearing conversion on an exchange basis? ( I don’t have a MkIII, but just asking).

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Yes