Checking The Cylinder Bore; Checking The Piston Clearance; Checking The Piston Ring - Yamaha 250GETO Service Manual

Checking the cylinder bore

1. Measure the cylinder bore (D
measuring points a, b, and c, and in
direction d (D
, D
1 3
to the crankshaft, and direction e (D
D , D ), which is at a right angle to the
4 6
crankshaft.
c
d
e
a: 10.0 mm (0.39 in) from the cylinder head top
surface
b: 5.0 mm (0.20 in) above the exhaust port
upper edge
c: 5.0 mm (0.20 in) below the scavenging port
lower edge
Cylinder bore (D
90.000–90.020 mm
(3.5433–3.5441 in)
Cylinder gauge 1:
90890-06759

Checking the piston clearance

1. Calculate the piston clearance using the
piston outside diameter and the cylinder
bore specifications. Replace the piston
and piston rings as a set or the cylinder
block or all parts, or rebore the cylinder if
out of specification.
NOTE:
Be sure to rebore the cylinder for matching
the replacement oversize pistons, when using
the specified oversize pistons.
Piston clearance:
0.155–0.161 mm
(0.0061–0.0063 in)
6S35H11
—D ) at
1 6
, D ), which is parallel
5
,
2
1
a
b
6F650370
–D ):
1 6

Checking the piston ring

1. Check the piston ring dimensions of B
and T. Replace the piston and piston
rings as a set if out of specification.
Piston ring dimension
Top ring and 2nd piston ring:
B: 1.970–1.990 mm
(0.0776–0.0783 in)
T: 2.700–2.900 mm
(0.1063–0.1142 in)
Crankcase
B
T
69D50410
5-32
1
2
3
4
5
6
7
8
9