Crankshaft Inspection; Main-Bearing Oil Clearance - Yamaha F20A Service Manual

POWR
CRANKCASE, CRANKSHAFT ASSY., AND CYLINDER
BODY
2. Measure:
Side clearance a
Out of specification → Replace the
piston and piston rings as a set.
Side clearance:
Top piston ring:
0.04 ~ 0.08 mm
(0.002 ~ 0.003 in)
2nd piston ring:
0.03 ~ 0.07 mm
(0.001 ~ 0.003 in)

Crankshaft inspection

1. Measure:
Crankshaft runout
Out of specification → Replace the
crankshaft.
Crankshaft runout limit:
0.03 mm (0.0012 in)

Main-bearing oil clearance

1. Measure:
Main-bearing oil clearance
Out of specification → Replace the
bearings as a set.
Main-bearing oil clearance:
0.012 ~ 0.044 mm
(0.0005 ~ 0.0017 in)
Measuring steps:
CAUTION:
Install the bearings in their original posi-
tions. Incorrect oil clearance measure-
ments can lead to engine damage.
Clean the bearings, main journals, and
bearing portions of the crankcase and
cylinder body.
Place the cylinder body upside down
on a bench.
Install half of the bearings 1 and the
crankshaft 2 into the cylinder body 3.
NOTE:
Align each bearing projection a with the
notch in the cylinder body.
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