The mixer is about 20 years old but not used a lot
When last used on slow speed to mix crumble it started smoking after use. I have dismantled the mixer and there are no visible overheating problems I reconnected the motor (part No. 27912) and ran the motor on its own and it remained cool. There was however some sparking at one of the brushes at all speeds

david gentle, August 2007

Some sparking!

The brushes do wear and I have changed mine now twice in the 19 years to 2003.

The minimum length is about 8mm, new= 18mm.
Pt No 602834 (W=7mm d=5.5mm)

I normally try to 'dress' the commutator. Last time I checked the dia. was 0.953 inches but I am not sure how much more meat is left.

I am about to investigate exactly the same problem.

Stuart T, October 2008