1979 Ski-Doo Supplementary Shop Manual, Page 69Get this manual
SECTION 04 SUB-SECTION 02 (ENGIN ES )
To correctly install the rotary valve disc proceed as follows:Turning crankshaft counter-clockwise, (drive pu ll ey side) bring magneto side piston to Top Dead Center using T.D.C gauge- Position the rotary valve disc on gear to have edges as close as possible to the marks
(2) th rough Rotary valve shaft assembly To remove rotary valve shaft assembly from crankcase, first remove coo lant pump impel ler and circlip Using the suitable pusher (PIN 420876610) and fiber hammer, push shaft assembly
NOTE: The rotary valve disc is asymmetrical, therefore, at assembly try positioning each side of disc on gear to determine best installation position