Quote:
Originally Posted by Bob Bidonde
Causes of the camshaft thrust knock are:
> the distributor - oil pump drive gear;
> the camshaft & crankshaft timing gears;
> thrust plunger & spring.
The distributor - oil pump drive gear mesh with the camshaft is affected by the condition of the bushings in the distributor and oil pump. The mesh is also effected by the condition of the spring acting on the drive gear in the valve chamber.
The mesh of the drive gear with the camshaft is adversely affected when there is shaft play due to worn bushings and or the spring is defective. The drive gear usually wears significantly, and if not corrected, the camshaft gear teeth will also wear.
The camshaft & crankshaft timing gears have straight cut teeth, and when these teeth wear, the meshing surfaces become sloped so they impart a thrust on the camshaft. When the gear teeth wear is substantial, the thrust force is enough to overwhelm the plunger spring. Having an aluminum camshaft gear driven by a steel crankshaft gear is not a durable situation because the aluminum gear is too soft. A better choice is a bronze camshaft gear or a fiber one.
The above conditions take their toll on the plunger and spring. Moreover, when the camshaft moves it imparts side loads on the valves that will effect the valve guide wear.
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The camshaft and crank gears are not straight cut. They are helical and run smooth when new. Aluminum and steel will run almost forever in an oil bath and when matched correctly.