A cap across PN is probably just a filter cap BUT it sounds like you have
start winding issues or a damaged commutator or winding.

(1) If the motor is a universal motor. then the open circuit cap may have
allowed spikes which caused damage. You may have lost a commutator segment.
Note the rotational position where the motor needs flick starting. If it is
always in the same location to within a commutator segment spacing that may
well be the cause.

This could be due to a damaged commutator segment contact or to an O/C
winding. If it has a comm, clean it and look for damage. If that does not
 help then it's probably a winding and not economically repairable. A rotor
from another grinder which is otherwise discombobulated may work.

(2) If the motor is an induction motor (less likely?) then  you may have a
starting winding which is usually in series with the cap and then there may
be a starter switch that opens when the motor is running or the motor may
be (more likely) a cap-run type where the capacitor and winding are always
in circuit..

The non starting may mean that you have a damaged starting circuit -
capacitor, winding, switch ...

 Russell
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.