1985 Ski-Doo snowmobile Service Manual, Page 198Get this manual
Section 02 ENGINE Sub-section 09 (537 ENGINE TYPE)
INSPECTION
1,5, Rotary valve coverrotary valve
A gap of 0.270.48 mm LOll.019") must be maintained between the rotary valve and the crankcaseTo measure this gap use feeler gage inserted between rotary valve and upper crankcase with the rotary valve cover in place without it's O-ringCheck as much surface as possibleFollow the same procedure for the lower crankcase