CYLINDER HEAD
Page 4A-28 90-857046R1 NOVEMBER 2001
Cleaning/Inspection/Repair
Camshaft
Manual start models are equipped with a cam shaft featuring a compression release
mechanism. The compression relief mechanism releases a percentage of the cylinder
compression during engine cranking, which lowers the starter rope pull force.
At cranking speeds (RPM) the cam shaft decompression levers rest against the side of the
exhaust cam lobes, protruding out from the heal of the lobe. This protrusion contacts the
exhaust valve rocker arms during the compression stroke, slightly opening the exhaust
valve.
With the increase of centrifugal force at engine running speeds, the decompression levers
swing out of contact with the exhaust valve rocker arms, allowing the exhaust valves to operate
normally (fully closed) during the compression stroke.
b
a
a-Exhaust Valve Rocker Arm
b-Decompression Lever
1. Inspect the camshaft for pitting, heat discoloration, or scratches, and for the following
measurements. Replace camshaft if worn or not within specification.
2. Inspect the compression relief cam lever (if equipped) for free movement. Replace cam-
shaft if necessary.
a
a-Compression Relief Cam
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