Yamaha pw80 - Manual (Page 36)

2. Check cylinder bore. Using a cylinder
hone, remove any scoring. Hone lightly,
using smooth stones. Hone no more than
required to avoid excess piston clearance.
Piston
1. Using a scraper, remove carbon deposits
from piston crown.
2. Break a used piston ring in two. File end
square. De-burr edges to avoid scratching
ring groove and clean carbon deposits
from ring grooves.
3. Using 400 ~ 600 grit wet sandpaper, lightly
sand score marks and lacquer deposits
from sides of piston. Sand in a crisscross
pattern. Do not sand excessively.
Piston clearance
1. Cylinder bore measurement
Using a cylinder gauge set to standard
bore size, measure the cylinder. Measure
front-to-rear and side-to-side at top.
center and bottom just above exhaust
port. Compare minimum and maximum
measurements. If over tolerance and not
correctable by honing, rebore to next
oversize.
2
.
Piston outside diameter measurement
Using an outside micrometer, measure
piston diameter. The measuring point is
at right-angles to the piston pin holes,
about 5 mm (0.2 in) from the bottom of
the piston skirts.
Make a correct calculation of the piston
clearance using the following formula.
• PISTON CLEARANCE
= Minimum Cylinder Diameter
- Maximum Piston Diameter
EXAMPLE:
PISTON CLEARANCE
= 47.000 mm-46.965 mm = 0.035 mm
(1.8504 in-1.8490 in = 0.0014 in)
Norminal piston clearance
0.033-0.038 mm (0.0013-0.0015 in)
-24-