Check Valves; Piston And Piston Rings - Mercury 45 Jet 50-55 Service Manual

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.
If a cylinder bore is tapered, out-of-round or worn
more than .003 in. (0.08 mm) from standard "Cylin-
der Block Finish Hone" diameter (refer to chart), it will
be necessary to rebore that cylinder(s) to designated
oversize bore and install oversize piston(s) and pis-
ton rings during reassembly.
NOTE: The weight of an oversize piston is approximately
the same as a standard size piston; therefore, it is not nec-
essary to rebore all cylinders in a block just because one
cylinder requires reboring.
IMPORTANT: Ports must be deburred after honing.
After honing and thoroughly cleaning cylinder bores,
apply 2 cycle outboard oil to cylinder walls to prevent
rusting.

Check Valves

NOTE: Check valves can be replaced by removing intake
manifold when powerhead is attached to driveshaft hous-
ing.
The check valves are a 3/16 in. (4.76 mm) diameter brass
casing containing a nylon ball-valve. These can be dam-
aged by hot combustion blow-by into crankcase (ie.: back-
fire, or a hole in top of piston, etc.).
4-22 - POWERHEAD
TO CHECK: Inspect check valves by looking through hole.
If light can be seen the nylon ball is bad (probably melted);
REPLACE valve. If you see no light, insert fine wire into
check valve hole to see if there is slight movement of nylon
ball. If ball moves, valve is O.K.. Replace valve if ball does
not move.
Install check valve into check valve holder as shown.
TOP
CENTER
BOTTOM
a - Check Valve
b - Holder

Piston and Piston Rings

IMPORTANT: If engine was submerged while engine
was running, piston pin and connecting rod may be
bent. If piston pin is bent, piston must be replaced. Pis-
ton 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 "Connect-
ing Rods" for checking straightness).
Air
Air
Inspect piston for scoring and excessive piston skirt
wear.
Check tightness of piston ring locating pins. Locating
pins must be tight.
Thoroughly clean pistons. Carefully remove carbon de-
posits, with a soft wire brush or carbon remover solu-
tion. DO NOT burr or round off machined edges.
Inspect piston grooves for wear and carbon accumula-
tion. If necessary, scrape carbon from piston ring
grooves being careful not to scratch sides of grooves.
Refer to procedure for cleaning piston ring grooves.
a
b
PE-51080
90-817643R1 DECEMBER 1996