Standard Player Action slide valves should be adjusted so that the
slider uncovers the port to the pneumatic with about 1/16-inch
clearance above the opening.

The adjustment needs to be close, but is not something that needs to
be measured with ruler by any means.  You can certainly eyeball it.
If the crankshaft is straight, and the sliders are adjusted correctly
and the motor still does not run smoothly on low vacuum, it is probably
leaking elsewhere.

I refer you to my article in the MMD Archives regarding restoring the
Standard Pneumatic Co. player action wind motor [000818 MMDigest].

John D. Rutoskey - Automatic Music Machines
Baltimore, Maryland