i am in the process of rebuilding my 91 n/a and the manual mentions "soft material coating" on the side surfaces and i was wondering if i can still send a engine parts i.e. rotor housings, rotors, intake to be cleaned by a machine shop if it will hurt that soft material coating.

 

is that the nitride coating maybe? If so I think it's safe to have it cleaned, you just can;t machine the surface without removing the nitride . . .

 

By "cleaned" I am guessing you mean surface ground or lapped. The nitride coating is only a couple of mils thick so any surfacing goes right through it. Then they will wear much quicker.