Yamaha F150B Service Manual page 64

TECH
FEA
Technical features and description
Offset crankshaft
The crankshaft centerline is offset by 10.0 mm (0.39 in) from the centerline of the cylinder bore. The
offset positioning results in the disagreement of crankshaft TDC with piston TDC, and allows the dif-
ferent duration of compression stroke from that of combustion stroke. Such difference in compres-
sion stroke and combustion stroke makes it possible to cause the earlier expansion and to keep the
piston longer at around TDC after the ignition, leading to more effective use of combustion pressure
and improved combustion efficiency.
It is also useful to reduce the frictional loss because the piston side force, the force in the thrusting
direction generated on the piston during the combustion stroke, becomes smaller.
Crankshaft center line
Center line of cylinder bore
Offset 10.0 mm (0.39 in)
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