Yamaha EH63 Service Manual page 99

PISTONS, CAMSHAFT, CRANKCASE, AND CRANKSHAFT
a
P
TIP
Measure cylinder bore "C" by taking side-to-side and front-
to-back measurements of the cylinder.
Bore:
80.000–80.019 mm (3.1496–3.1503 in)
(EH63K/EH64A/EH64K/EH65A/EH65B)
84.000–84.022 mm (3.3070–3.3079 in)
(EH72A/EH72B/EH72K)
Warpage limit:
0.1 mm (0.0039 in)
"C" = maximum of D , D
1 2
b. If out of specification, replace the crankcase
assembly, and replace the piston and piston rings
as a set.
c. Measure piston skirt diameter "P" with the
micrometer.
a = 13.0 mm (0.5118 in) from the piston bottom
edge (EH63K/EH64A/EH64K/EH65A/EH65B)
a = 10.0 mm (0.3937 in) from the piston bottom
edge (EH72A/EH72B/EH72K)
Piston diameter:
79.960–79.980 mm (3.1480–3.1488 in)
(EH63K/EH64A/EH64K/EH65A/EH65B)
83.980–84.000 mm (3.3062–3.3070 in)
(EH72A/EH72B/EH72K)
Limit:
79.878 mm (3.1447 in) (EH63K/EH64A/
EH64K/EH65A/EH65B)
83.890 mm (3.3027 in) (EH72A/EH72B/
EH72K)
d. If out of specification, replace the piston and pis-
ton rings as a set.
e. Calculate the piston-to-cylinder clearance with
the following formula.
Piston-to-cylinder clearance = Cylinder bore "C" – Piston skirt
diameter "P"
3-55
, D , D , D , D
3 4 5 6
1
2
3
4
5
6
7
8
9
10