Cylinder Head Identification; Engine Rotation; Crankshaft; Piston And Connecting Rods - Mercury 305 CID Service Manual

Cylinder Head Identification

MCM 5.0L
MCM 5.7L/MCM 350 Magnum
IDENTIFICATION OF GEN + CYLINDER HEADS
The Gen + cylinder head has four 5/16 inch x 18 in-
take bolts verus six 3/8 x 16 bolts on cylinder head
prior to Gen +. There is not a provision for water
crossover in the center of the head.
a
a - Cylinder Head Prior To Gen+
b - Gen+ Cylinder Head
Index
3A-16 - ENGINES

Engine Rotation

Engine rotation terminology at times has caused
confusion. To clarify, engine rotation is determined
by observing flywheel rotation from the rear (trans-
mission or stern drive end) of the engine looking
forward (water pump end).
PROPELLER ROTATION IS NOT NECESSARILY
THE SAME as engine rotation.
When ordering replacement engines, short blocks or
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parts for engines, be certain to check engine rotation.
Do not rely on propeller rotation in determining en-
gine rotation.
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a - Left-Hand Rotation (CCW) - All Stern Drive Engines,
MIE Inboard LH (Standard) Rotation
b - Right-Hand Rotation (CW) - MIE Inboard RH (Opposite)
Rotation

Crankshaft

The crankshaft is supported in the block by five insert
type bearings. Crankshaft end thrust is controlled by
flanges on the No. 5 bearing. A torsional damper on
the forward end of the crankshaft serves to help
dampen any engine torsional vibration.

Piston and Connecting Rods

Piston pins are offset slightly toward the thrust side
b
of the pistons to provide a gradual change in thrust
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pressure against the cylinder wall as the piston
travels its path. Pins have a floating fit in the piston
and a press fit in the connecting rod (to hold them in
place).
a
b
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