1978 Ski-Doo Shop Manual, Page 55Get this manual
SECTION 02 SUB-SECTION 04 (DRIVEN PULLEY) (INSTALLATION
With drive chain tension released, hold upper sprocket and chain in position then insert assembled driven pulley shaft through chaincase and sprocketInstall spring washer and castellated nutTighten castellated nut fully then back off nut turnLock in position with new cotter pin_ CAUTION: It is important that nut is backed off or damage may occur due to burnt or seized bearing116
REMOVAL
Remove pulley guard and drive beltDetach driven pulley support from engine bracketRemove brake assembly and tool boxRemove chaincase coverRemove air silencer box and carburetorsRelease chain tension then remove cotter pin and castellated nut securing driven pulley to chaincasePullout driven pulley assembly