Finding Top Dead Center (Tdc); Method 1; Method 2 - Mercury MerCruiser Service Manual

2. Remove the rocker arm support assemblies and pushrods.
a
NOTE: Organize and store the rocker arm assemblies and pushrods in sets for assembly in their original locations.

Finding Top Dead Center (TDC)

IMPORTANT: Do not insert anything into a spark plug hole while turning the engine over.
0° timing mark on harmonic damper
a - Timing mark on harmonic damper
b - Timing mark on timing chain cover
NOTE: Cylinder number 1 is the foremost cylinder on the left side of the engine, as observed from the rear of the engine.
Position cylinder number 1 at TDC. Use one of the following methods:

Method 1

1. Remove the cylinder number 1 spark plug.
2. Attach a suitable socket wrench to the crankshaft pulley nut.
3. Place a finger over the plug hole and turn the engine over in its normal rotation until compression is felt in the number 1
cylinder.
4. Continue turning the engine over by hand until the block‑mounted timing pointer aligns with the 0° timing mark on the
harmonic damper.

Method 2

1. Attach a suitable socket wrench to the crankshaft pulley nut.
2. Remove the left (as observed from the rear of the engine) rocker arm cover and turn the engine in its normal rotation until
the number 1 cylinder intake valve is fully closed.
3. Continue turning the engine over by hand until the block‑mounted timing pointer aligns with the 0° timing mark on the
harmonic damper.
90-8M0099748 eng DECEMBER 2015
b
b
a
a - Rocker arm support assemblies
b - Pushrod
59510
54990
Pulley and belt removed for clarity
© 2016 Mercury Marine
Engine Disassembly
Page 3A-23