Bosch starter motor

Does anyone know the minimum length of the brushes or the correct spring pressure.


As you scroll down not only you get OEM part numbers, but brush sizes too. Don’t walk away just because it doesn’t say “Guzzi” on the tin. It is hard to reinvent a starter motor, so they are likely to be similar.

There is an excellent guide to stripping and rebuilding a Bosch starter on This Old tractor, unfortunately it doesn’t give a dimension for the brushes. I would say fit new ones if you have stripped it that far. They aren’t expensive

Good link Don, I rebuilt my starter motor about thirty years ago an it’s still going strong (or will be when I get the bike back on the road) I agree that if you have gone that far it would be daft not to replace the brushes, you never know when you will be back in there again!


I tarted mine up with silver Hammerite smooth and chromed the end cap while it was apart. The solenoid was new and is zinc plated.

Best of luck!

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Thanks for the replies, I’m aware they are not expensive and not that difficult to change. The motor is apart only because it sounded sluggish, battery/cables/connexions etc all good, not an unexpected amount of dust on the comm, now cleaned, so possibly brushes, I’m not someone who can approach fault finding with the attitude of keep changing parts until the fault goes away. While typing this I realise I have not looked at the state of the contacts in the solenoid.

I’m with Don, if you are that far into it, might as well, or you might have to take it apart again later! :grin:

If I find nothing else wrong then yes I agree with Don as well. Today I cleaned the gaps on the comm and checked resistance and insulation of the coils, the solenoid contacts were a little burned so they have been cleaned and burnished.
I hadn’t previously noticed but it is an 8 tooth motor and the case is marked 12v 0.6 P.S. , which I think is about 450 watts. I always thought 600w was the lowest power fitted. Perhaps that is why it struggles on a 950 but then again it always used turn over at a reasonable rate.