whit3rd wrote:

On Friday, February 3, 2017 at 3:28:30 PM UTC-8, wrote:

I have an old Baldor bench grinder. Probably 70 years old or older.
The motor is the type that uses a capacitor

I decided to run some numbers. The moment of inertia of the 8 inch
grinder wheels is approximately 3.16 times the moment for the 6 inch
grinder wheels.

The rotor is probably denser than the wheels, it might dominate.
One quick way to test a 400uF 330VAC capacitor, would be
to put a smaller known-good capacitor in parallel with it. If that
makes a big difference, the old capacitor needs replacement.

Look for a date on the capacitor (and if you replace it, write a date on
the new one); tracking the history sometimes simplifies things.
I seriously doubt the run capacitor is anywhere NEAR 400 uF. It would be as
big as a toaster in 1950 technology. Maybe 40 uF, but even that sounds big
for a run cap.

Jon