Mercury Optimax 115 Service Manual page 251

POWERHEAD
3. Measure cylinder bore diameter (with a snap gauge micrometer) of each cylinder, as
shown below. Check for tapered, out-of-round (egg-shaped) and oversize bore.
135/150 Models
Standard Piston Bore
.015 in. (0.381mm) Oversize Piston Bore
4. If a cylinder bore is tapered, out-of-round or worn more than 0.003 in. (0.076mm) from
standard "Cylinder Block Finish Hone" diameter (refer to chart, preceding), it will be
necessary to re-bore that cylinder(s) to 0.015 in. (0.381mm) oversize or re-sleeve and
install oversize piston(s) and piston rings during reassembly.
NOTE: The weight of an oversize piston is approximately the same as a standard size
piston; therefore, it is not necessary to re-bore all cylinders in a block just because one
cylinder requires re-boring.
5. After honing and thoroughly cleaning cylinder bores, apply light oil to cylinder walls
to prevent rusting.
Pistons and Piston Rings
IMPORTANT: If engine was submerged while engine was running, piston pin and/or
connecting rod may be bent. If piston pin is bent, piston must be replaced. (Piston
pins are not sold separately because of matched fit into piston.) If piston pin is
bent, connecting rod must be checked for straightness (refer to "Connecting
Rods," following, for checking straightness).
1. Inspect pistons for scoring and excessive piston skirt wear.
2. Check tightness of piston ring locating pins. Locating pins must be tight.
3. Thoroughly clean pistons. Carefully remove carbon deposits from pistons, with a soft
wire brush or carbon remove solution. Do not burr or round off machined edges.
Inspect piston ring grooves for wear and carbon accumulation. If necessary, scrape car-
bon from piston ring grooves being careful not to scratch sides of grooves. Refer to
procedure following for cleaning piston ring grooves.
Page 4A-28
Models
51846
Cylinder Block Finish Hone
3.501 in. (88.93mm)
3.516 in. (89.31mm)
90-855347R1 JANUARY 1999