No.1 piston on the compression stroke at top center (TC) is the reference point for all timing procedures.
LOCATING TOP CENTER
1. Timing pointer (aligned with mark on flywheel).
Remove the valve and rocker arm cover (the two valves at the front of the engine are the intake and exhaust valves for No.1 cylinder). Remove the plate on the left of the flywheel housing.
Rotate the crankshaft counterclockwise (as viewed from the flywheel end) at least 60°, until both the intake and exhaust valves of No.1 cylinder are closed.
Align the timing mark “TC 1” with the pointer (1). The No.1 piston is now positioned at top center (TC) on compression.