Two days before setting off for Silverstone, a last minute start-up of the Mouse race car induced total panic when the starter motor failed to start anything! The Mouse operates on 12 volts so the first conclusion was that I had burnt it out by previous over-zealous use. As the remedy would involve removing the old starter and replacing it somewhat urgently, I retrieved a couple of old starter motors from the depths of the “don’t throw anything away” store but, of course, neither of them worked. (See a previous Technical Tip about the inadvisability of keeping old coils!). However, one of them had its inspection ring missing and violent sparks were issuing from the brush gear. They say the most obvious remedy is always the least obvious! And, yes, all that was at fault was the brushes in the Mouse starter motor had worn down to the holding screws and were no longer doing their business. It may be possible to change the brushes without removing the starter motor from the engine but, as can be seen in the attached photos, I decided not to mess about and take the damn thing out to work on. However, removing the starter motor took much longer than replacing the brushes! However, starter motor brushes and dynamo brushes are NOT the same—starters have brass ones and dynamos have carbon so keep a set of each in store. David Whetton
| Lifting up the old brush against its spring shows just how badly it was worn. With a second screwdriver just unscrew the screw shown in the photo and the old brush falls out together with the screw but none of the spring mechanism. |
| When replacing the inspection cover, be careful not to bridge the round electrical contact on the top of the motor. |
| The starter bolts are notoriously difficult to get a spanner around so whilst I was at the job I cut a screwdriver slot in the ends with a hacksaw to aid future operations. |