1980 Ski-Doo Shop Manual, Page 68Get this manual
SECTION 03 SUB-SECTION 02, (ENGINES)
To correctly install the rotary valve disc proceed as follows:Turning crankshaft counter-clockwise(drive pulley side) bring magneto side piston to Top Dead Center uSing T.D.CgaugePosition the rotary valve disc on gear to have edges as close as possible to the marks
(2) through Rotary valve shaft assembly
To remove rotary valve shaft assembly from crankcase, first remove coolant pump impellerandclrclip0Using the suitable pusher (P 420 876 610) and fiber hammerpush shaft assembly
NOTE: The rotary valve disc IS asymmetricalthereforeat assembly try positioning each side of disc on gear to determine best installation position