Cylinder Block - Yamaha 20C Service Manual

POWR
INSPECTION
G61501-0*

CYLINDER BLOCK

Cleaning
1) Using a gasket scraper, remove all traces of
gasket material from the cylinder-block surface.
2) Using a soft brush and solvent, clean the cylin-
der-block.
Inspection
1) Visually inspect the cylinder sleeves for cracks
and scratches.
If cracks are found, replace the cylinder block.
If scratches are found, check the degree of out-
of-round, and then hone the cylinder or re-bore
it if necessary.
2) Using a cylinder-gauge, measure the cylinder
bore at three positions in the thrust and axial
directions.
1 Axial direction
2 Thrust direction
A: 10 mm (0.4 in) below the cylinder top
B: 10 mm (0.4 in) above the exhaust port
C: 5 mm (0.2 in) below the scavenging port
NOTE:
Do not place the cylinder-gauge on the port hole.
Cylinder bore size:
67.000 – 67.020 mm
(2.6378 – 2.6386 in)
Maximum allowable taper:
0.08 mm (0.0032 in)
Maximum allowable out-of-round:
0.05 mm (0.0020 in)
If diameter is greater than the maximum allowable,
hone or rebore the cylinder or, if necessary, replace
the cylinder-block.
5-16
E