Honda CB350 Repair Manual page 66

ENGINE AND TRANSMISSION 61
Scoring on this piston was caused by a seizure
der is either larger than the service limit
using the largest measurement obtained
or has more taper than the service limit,
(subtract the smallest measurement from
the largest in a plane perpendicular to
the wrist pin), the cylinder should be
bored to the next oversize and a new
oversize piston fitted.
3. Make a visual inspection of the pis—
ton. Scoring, scuffing, or seizure marks on
the piston skirt can be removed with a
fine grade of emery or crocus cloth, sand—
ing in a crosshatch pattern, if not too se—
vere. If the damage is severe, the piston
must be replaced.
4. The rings must be free to move in
the ring grooves. If they cannot, either
they are carbon clogged (which necessi—
tates replacing the rings and cleaning the
grooves), or metal has been pushed into
Removing score marks from the skirt with emery
cloth: produce a crosshatch pattern when sanding
the grooves by seizure of the piston, or
the piston crown has been collapsed from
hitting a valve. In this event the piston
and rings must be replaced.
5. Measure the piston at the bottom
ofthe skirt perpendicular to the wrist pin.
If the diameter is less than the service
limit given in the "Engine Specifica—
tions" chart, the piston must be replaced.
If this has happened, it is probable that
the cylinder is worn as well and the solu—
tion is to have the cylinder bored out to
the next oversize.
Measuring piston diameter
NOTE: The piston and bore specifica—
tions in the "Engine Specifications"
chart are for standard pistons. Over—
size pistons have the oversize stamped
on the piston crown. Oversize pistons
are available in four oversizes from
Honda (0.25, 0.50, 0.75, and 1.0 mm).
New pistons come with the wrist pin
and rings. If an oversize piston is
needed due to a worn bore or worn or
damaged pistons, obtain the piston
first then take the piston and cylinders
to your dealer or machine shop and
have the cylinder bored so that the
piston—to—cylinder wall clearance is
0.025—0.050 mm (0.001—0.002 in.).
6. If an inside micrometer is avail—
able, measure the inside diameter ofthe
wrist pin hole and compare the measured
value to the service limit. The wrist pin
should be a light slip fit into the holes. If
too loose, the piston should be replaced.
7. Check the condition of the wrist
pin. Measure the diameter of the wrist
pin at three places along its length and
compare the diameter with the standard
specification for your model. If worn
beyond the service limit or if the pin is
discolored from overheating, it should be
replaced.
8. The wrist pin rides directly on the
connecting rod small end. Measure the
inside diameter of the small endif possi—
ble and compare your findings with the