1985 Ski-Doo snowmobile Service Manual, Page 342Get this manual
253 ENG INE TYPE
Section 04 ELECTRICAL Sub-section 02 (IGNITION TIMING)
ELECTRONIC IGNITION SYSTEMS Two methods are detailed in this section, the first one using top dead center gauge to check the flywheel timing markThe second one using stroboscopic timing light to verify ignition timing
NIPPONDENSO
3Rotate the crankshaft until the piston is at: DIRECT TIMING: 2.31 mm (.091) B.T.D.CBTDC: Before top dead centerAt this point, the crankcase central mark and the flywheel mark MUST alignIf the marks do not correspond to the specification, scribe new mark on the flywheelTiming marks verification cannot be used as timing procedure, therefore, always check the timing (using stroboscopic timing light) at 6000 R.P.Mafter the marks have been alignedCAUTION:
Top dead center gauge verification
1Disconnect spark plug wire and remove spark plug2Install and adjust T.D.Cgauge on engine as follows:Rotate magneto clockwise until piston is just before top dead center- With gauge in adaptor, adjust roller so that it is parallel with dial faceTighten roller lock nut