11-3
SECTION 11: CRANKSHAFT & CAMSHAFT
2. Inspect the crankshaft bearing bore in the crankcase cover
for damage and wear (Figure 11-7).
a. Measure the Inside diameter of the bearing bore.
b. If the bore is worn excessively, replace the crankcase
cover.
Figure 11-6. Crankshaft Sleeve Bearing
CRANKSHAFT
BEARING
BORE
CRANKCASE
COVER
Figure 11-7. Bearing Bore in Crankcase Cover
COMPRESSION RELEASE
A mechanical compression release is provided on the cam-
shaft (Figure 11-8). A flyweight pivots on a pin mounted in
the camshaft gear. The pin itself has a cam action. When the
engine is not running, the pin holds the tappet up just slightly,
which in turn holds the exhaust valve slightly open. This relieves
compression for easier cranking.
When the camshaft spins, the flyweight moves, causing the
pin to turn. The tappet is then free to move normally.
Measure the amount of compression relief lift at the tappet
(see Figure 11-9). See SPECIFICATIONS in Section 14 (Small
Frame) or Section 15 (Large Frame) for measurements.
Figure 11-8. Compression Release Mechanism
TAPPET
CAMSHAFT
COMPRESSION
RELIEF LIFT
CAM LOBES
Figure 11-9. Compression Relief Lift
CRANKSHAFT INSTALLATION
Before installing the crankshaft, lubricate all bearing surfaces
with engine oil. Seal protectors should be used to prevent
damage to oil seals during installation. Install the crankshaft
as follows:
1. Lubricate all bearing surfaces with engine oil.
2. Install the valve tappets.
3. Support both ends of the crankshaft and carefully install
into the crankcase.
11
0C1103Arev0.indd 3 6/22/2006 10:51:34 AM
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