1978 Ski-Doo Shop Manual, Page 202Get this manual
SECTION 04 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.Cgauge- Position the rotary valve disc on gear to have edges as close as possible to the marks
If it is necessary to disassemble components of rotary valve shaft assembly, install assembly carefully in vise compressing spring cup in order to remove circlip
NOTE: The rotary valve disc is asymmetrical, therefore, at assembly try positioning each side of disc on gear to determine best installation positionMagneto side piston must be at T.D.C
Clean rotary valve shaft and inside of distance sleeveAt assembly, apply Loctite Lock'n Seal 271 inside of distance sleeve
Using suitable pusher, push water pump bearing
with shield facing rotary valve disc