Airhead starter motors
Posted: Sun 01 Jul, 2018 8:31 pm
My R90S has been very difficult to start of late, particularly on a cold morning. I have a good battery in the bike, so dived into the starter as soon as I got back from Jennacubine. I was surprised to see that my bike is fitted with an 8 tooth starter motor! I was so sure it was a 9 tooth because from mid '75 BMW made the change. My R90S is a Feb 1976 model. Of course the ring gear on the flywheel is different for the two different types. I suppose it is possible that the previous owner fitted an older flywheel and starter. The good news for me is that I had two 8 tooth starter motors in my stock of spares, one which has been refurbished. On disassembling my starter motor I found that not only were the brushes on the short side but the field windings were black from my sustained attempts at slow cranking and smelt like a freshly burnt forest. I think only my bendix is worth keeping. I guess the moral of the story is, be aware that your model may be equipped with an earlier (or later) component which is close to what you need but won't do the job.