HYOSUNG Prima Service Manual page 48

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 the 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
reduced 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 service
limit, replace it with a new one.
Dial calipers : 09900 - 20605
Piston pin bore I.D.
Standard
Serivice limit
41.005~41.020 mm
41.070 mm
40.935~40.950 mm
40.885 mm
0.065~0.075 mm 0.120 mm
Service limit 10.030 mm
ENGINE 3-20