I have toothed pulleys on my crossflow (crank, water pump and alternator) with toothed belt (aka Gates belt).

I notice that the pulley is off a little bit of the alternator pulley - picture shows it exaggerated.

Should I be worried?

The crank pulley has sides as shown in piccy so the belt should not fly off.

And how to fix it? I think if I shim the alternator mount out so that the rear of the pulley is a bit furtner out, the belt will want to run to the smaller diameter circle i.e. the front.

Otherwise I need to make new alternator mount to put the alternator further forwards.

Which would be the better?
Rescued attachment pulley.JPG

Belts tend to move to the larger diameter if a pulley is not parallel. This is how early flat belts used on lathes, farm machinery etc. stayed on the pulleys.

Similar problem on mine. Local expert reckoned a 5mm run-out is acceptable but no more.
Cheers, Pewe