HYOSUNG WOW90 Service Manual page 50

As a result of the above measurement, if the piston-
to-cylinder clearance exceeds the following limit,
overhaul the cylinder and use an oversize piston, or
replace both cylinder and piston. The measurement
for the bore diameter should be taken in the intake-
to-exhaust port direction and at 20mm from cylinder
top surface.
Cylinder bore
Piston diameter
Cylinder to piston
clearance
◉ DE-CARBONING
De-carbon the piston and piston ring grooves, as illus-
trated. After cleaning the grooves, fit the rings and
rotate them in their respective grooves to be sure that
they move smoothly.
Carbon in groove is liable to cause the piston ring to
get stuck in the groove, and this condition will lead to
reduce engine power output.
A piston whose sliding surface is badly grooved or
scuffed due to overheating must be replaced. Shallow
grooves or minor scuff can be removed by grinding with
emery paper of about #400.
◉ PISTON PIN BORE I.D.
Using a caliper gauge, measure the piston pin bore
inside diameter. If reading exceeds the following ser-
vice limit, replace it with a new one.
Piston pin bore I.D.
Dial calipers : 09900-20605
Standard
Service limit
52.500~52.515mm 52.590mm
(2.0669~2.0675 in) (2.0705 in)
52.432~52.447mm 52.332mm
(2.0643~2.0648 in) (2.0603 in)
0.120mm
0.073 ~ 0.083mm
(0.0029~0.0033 in) (0.0047 in)
Service limit
12.030 mm (0.474 in)
ENGINE 3-22