1978 Ski-Doo Shop Manual, Page 172Get this manual
SECTION 04 SUB-SECTION 02, (ENGINES) (If it is necessary to disassemble components of rotary valve shaft assembly, install assembly carefully in vise, compressing spring retaining cup in order to remove cirlip
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.O.Cgauge- Position the rotary valve disc on gear to have edges as close as possible to the marks
NOTE: The rotary valve disc is asymmetrical, therefore, at assembly try positioning each side of disc on gear to determine best installation position
' Magneto Side piston