Mercury 90 Service Manual

90-830234R3 DECEMBER 1997 POWERHEAD - 4-41
CYLINDER BORE SIZE
Piston Size Cylinder Block Fin-
ish Hone
Standard Diameter 3.501 in.
(88.77mm)
0.015 Oversize 3.516 in.
(89.15mm)
0.030 Oversize 3.531 in.
(89.54mm)
• Inspect cylinder bores for scoring (a transfer of
aluminum from piston to cylinder wall). Cylinder
wall scoring usually can be “cleaned up” by hon-
ing or reboring.
When reboring cylinder block, remove hone fre-
quently and check condition of cylinder walls.
DO NOT hone any more than absolutely neces-
sary, as hone can remove cylinder wall material
rapidly.
HONING PROCEDURE
• Follow hone manufacturer’s recommendations
for use of hone cleaning and lubrication during
honing.
IMPORTANT: After honing, bores should be thor-
oughly cleaned with hot water and detergent.
Scrub well with stiff bristle brush and rinse with
hot water. If any abrasive material is allowed to
remain in the cylinder bore, it will cause a rapid
wear of new piston rings and cylinder bore. After
cleaning, bores should be swabbed several
times with 2 cycle engine oil and a clean cloth.
Wipe excess oil with clean, dry cloth. Cylinders
should not be cleaned with kerosene or gasoline.
Clean remainder of cylinder block.
• Hone all cylinder walls just enough to de-glaze.
• Measure cylinder bore inside diameter (with an
inside micrometer) of each cylinder, as shown
below. Check for tapered, out-of-round (“egg-
shaped”) and oversize bore.
A
B
C
• If a cylinder bore is tapered, out-of-round or
worn more than 0.003 in. (0.08mm) from stan-
dard “Cylinder Block Finish Hone” diameter (re-
fer to chart), it will be necessary to rebore that
cylinder(s) to designated oversize bore and
install oversize piston(s) and piston rings during
reassembly.
NOTE: The weight of an oversize piston is approxi-
mately the same as a standard size piston; therefore,
it is not necessary to rebore all cylinders in a block
just because one cylinder requires reboring.
IMPORTANT: Ports must be deburred after hon-
ing.
• After honing and thoroughly cleaning cylinder
bores, apply 2 cycle outboard oil to cylinder walls
to prevent rusting.

Mercury 90 Specifications

General

Brand	Mercury
Model	90
Category	Outboard Motor
Language	English