Camshaft Thrusting Knock

[mantta]

I have that annoying knock from the cam thrusting back and fourth when the engine is first started. After a few minutes of running it is no longer heard. I replaced the spring and plunger in the gear cover but it still does it. I have the aluminum gear and that makes it even louder. Would binding in the pump drivecause this? I even thought of modifying a timing gear cover, removing the plunger and spring and drilling and tapping the plunger hole and putting in an adjustable thrust screw. I read about this somewhere in this forum but can not locate it. Have any of you tried this? Thanks for any input you can give me.

 

[RHD]

It sounds as though the cam plunger spring tension is not sufficient. The cam should not move back and forward no matter how cold the engine is. I know this spring has to be quite strong to do it's job. I wouldn't modify anything. Model 'A's were perfect just the way they were made.

 

[85930tudor]

I have a engine that has been modified like you are talking about, and think that I started that thread. i have the engine apart now. if possible i will post pics ......Dave

 

[pat in Santa Cruz]

read the thread on the complaint about the Antique Engine Rebuilder...the supposed cause of the cam slamming was a defective drive gear. I had a pounding camshaft last week in a customers car. The plunger spring was some home made thing, not very strong. Replacing it with the correct one did the trick. That car also had a missing oil pump drive gear retainer spring....man, was that ever noisy. sounded like a cold cummins diesel.

I believe Taylor Engines makes a cam thrust screw with a torrington bearing on it.

 

[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.

 

[just plain bill]

This is a more extreme modification. This was done because of oversized big ends on aluminum connecting rods reduced clearance when the oil pressure was too high and the cam moved enough to slightly gouge the rods. Don't believe this could happen on stock engine but posted this to illustrate solid cam stop I use on all of my engines

 

[Jim Brierley]

Very nice Bill. Me being lazy, I just drill and tap the cover for a 3/8" allen screw and use it to but up against the stock plunger. spot face the cover for a jam nut. The cover is thin in this area, so use caution.

 

[V4F]

there are people out there that make a great billet cover with threaded plunger ! i have one & it work fine ......... steve

 

[James Rogers]

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.

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.

 

[James Rogers]

I have never seen ones with straight cut teeth.
Originals and all replacements I have seen are all helical cut teeth.

Vince, the only straight cut camshaft and crank gears Ford ever used were on the early T's. Must have made a lot of noise since he discontinued them early on.