Just a thought, if u are having trouble finding a "Commutator Stone".....follow this link. It is an Australian company and will give you an idea of the product to assist you.
http://www.morgancarbon.com.au/Maint%20products%202.pdf
Depending on the damage/severity you have on-site, this may get...
Hi a70duster how are u,
I have completed this type of job many times on draglines, lift motors, winder motors and electric trucks (Komatsu).
1. How far out of round is the commutator...have u checked with a dial gauge to confirm your theory? If it is out of round you will notice excessive...
Did you take note of the ambient temp. whilst performisng the test, and the temp. of the stator itself?
Sounds like the winding is very dry and a good steam clean, varnish and bake may do the job. Good Luck