1970-1979 Ski-Doo Snowmobiles Service Manual, Page 136Get this manual
POWER TRAIN 3Lay 19 in(48 em) length of Ys insquare bar between pulley halves (Figure 26)4Check pulley offset and distance as specified in Table 35On front mounted engines if pulley offset is out of tolerance, loosen engine support and adjust in required direction to obtain specified offset6On center mounted engines, remove drive pulley and add shims to crankshaftCAUTION
CHAINCASE, DRIVE CHAIN, AND SPROCKETS Pressed Steel Chaincase Assembly RemovalInstallation 1Remove driven pulley2Release track tension (Chapter Two)3Place drain pan beneath chaincase and pry out drive axle oil seal from chaincase with small screwdriver (Figure 27)4Disconnect brake cableNOTE: On 1970 models with 18 intrack, remove foot rest secured to frame and chaincase(Figure28)