General; Engine Identification; Engine Rotation; Firing Order - MerCruiser GM4 Service Manual

General

Some of the repairs in this section must be completed
with engine removed from boat. Engine removal de-
pends upon type of repair and boat design. Place en-
gine on repair stand for major repairs.
When engine removal is not required, make certain
that battery cables are disconnected at the battery
prior to performing any on-board engine repair proce-
dure.
Lubricate all moving parts (during reassembly) with
engine oil. Apply Quicksilver Perfect Seal on threads
of and under heads of cylinder head bolts, and on
threads of all cylinder block external bolts, screws
and studs.
No. of
Model
Cylinders
MCM 3.0L/3.0LX

Engine Identification

The MerCruiser Model can be determined by looking
at the LAST TWO LETTERS of the engine code
stamped into the cylinder block. This code number is
stamped on all MerCruiser power packages and re-
placement partial engines, but not replacement cylin-
der block assemblies.
If the engine serial number and/or model decals are
missing, the engine code letters may help in deter-
mining the engine models.
3.0L uses the 2.5L cylinder head
3.0LX uses the 3.0L cylinder head
a - 4 Cylinder-In-Line Engine Code (Next To Distributor)
G.M. Engine Code Location
MCM Stern Drive Engines (LH Rotation)
3.0L - RM, RJ
3.0LX - RN, RK
Index
3A - 6 - ENGINES
Cu. In./Litres
Displacement
4 181 (3L)
a
74520

Engine Rotation

Engine rotation terminology at times has caused con-
fusion. To clarify, engine rotation is determined by ob-
serving flywheel rotation from the rear (transmission
or stern drive end) of the engine looking forward (wa-
ter pump end).
PROPELLER ROTATION IS NOT NECESSARILY
THE SAME as engine rotation. Do not rely on propel-
ler rotation in determining engine rotation.
a - Left-Hand Rotation (CCW) - All Stern Drive Engines

Firing Order

a
72001
90-816462 2-695