Yamaha F25A - Crankshaft Inspection; Main-Bearing Oil Clearance

5-38
POWR
E
CRANKCASE, CRANKSHAFT ASSY., AND CYLINDER
BODY
2. Measure:
● Side clearance a
Out of specification → Replace the
piston and piston rings as a set.
Crankshaft inspection
1. Measure:
● Crankshaft runout
Out of specification → Replace the
crankshaft.
Main-bearing oil clearance
1. Measure:
● Main-bearing oil clearance
Out of specification → Replace the
bearings 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 runout limit:
0.03 mm (0.0012 in)
Main-bearing oil clearance:
0.012 ~ 0.044 mm
(0.0005 ~ 0.0017 in)
Measuring steps:
● 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.
CAUTION:
Install the bearings in their original posi-
tions. Incorrect oil clearance measure-
ments can lead to engine damage.
NOTE:
Align each bearing projection a with the
notch in the cylinder body.