Dear Sam

The bearings should normaly last a good bit longer.

If the clutch is set too soft, it will be slipping a bit. Slipping in a clutch cause vibrations wich will be transferred to the bearings, and then wear them out more quickly. Slipping in a clutch is more likely when braking an engine in then at racing.

Make sure the clutch engage fully, also when you break in engines, and you will observe that the bearings last much longer.

Best wishes; Jens