Mercury MerCruiser MCM 454 Mag MPI Service Manual page 288

454 CID (7.4L) / 502 CID (8.2L)
3. When finish-honing a cylinder bore to fit a piston, move hone up and down at a sufficient
speed to obtain very fine uniform surface finish marks in a crosshatch pattern of approxi-
mately 30 degrees to cylinder bore. Finish marks should be clean but not sharp, free
from imbedded particles and torn or folded metal.
4. Permanently mark piston (for cylinder to which it has been fitted) and proceed to hone
cylinders and fit remaining pistons.
IMPORTANT: Handle pistons with care and do not attempt to force them through
cylinder until cylinder is honed to correct size, as this type piston can be distorted
by careless handling.
5. Thoroughly clean cylinder bores with hot water and detergent. Scrub thoroughly with a
stiff bristle brush and completely rinse with hot water. It is extremely essential that a good
cleaning operation be performed. If any abrasive material remains in cylinder bores, it
will rapidly wear new rings and cylinder bores in addition to bearings lubricated by the
contaminated oil. Swab bores several times with light engine oil on a clean cloth, then
wipe with a clean dry cloth. Cylinder should not be cleaned with kerosene or gasoline.
Clean remainder of cylinder block to remove excess material spread during honing
operation.
PISTON SELECTION
1. Check used piston to cylinder bore clearance as follows:
a. Measure cylinder bore diameter with a telescope gauge 2-1/2 in. (64 mm) from top
b. Measure piston diameter at skirt across centerline of piston pin as shown.
c. Subtract piston diameter from cylinder bore diameter to determine piston-to-bore
d. Determine if piston-to-bore clearance is in acceptable range shown in "Specifica-
Index
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of cylinder bore as follows.
clearance.
tions."
SERVICE MANUAL NUMBER 23
72570
72624
90-861326--1 MARCH 1999