engine knock

[FRANK PKNY]

I get a knock when I advanve the spark about 1/3 way on the sector. Would this be an indication of end play on the crankshaft or cam bearings or main bearings? Thanks

 

[Doug Money]

Have you checked to see if there is a lot of carbon on the piston tops or combustion chamber?

 

[FRANK PKNY]

Yes Doug the engine had a recent valve job just prior to my purchasing it. It also has aluminum pistons.

 

[Jack Innes]

Timing gears can sound like a knock.

If you take a broom stick, put your thumb over the end & press that thumb to your ear then place the other end against various areas on the engine. You can often narrow down where a noise is coming from. Some folks have a stethescope but that is too easy. (I do think I can tell more through the broom stick.)

 

[stevests]

Perhaps you should recheck the timing - could be an ignition knock.

 

[CharlieB]

More info please. Does it only appear when you advance the spark or do you also hear a knock on other occasions too? Such as pulling a hill or sudden acceleration (without spark lever movement). If it's just when moving the lever it could merely be a spark knock. Crank end play in itself will not cause this noise. A loose connecting rod might. Shorting each plug while the noise is occuring will isolate the cylinder if it's a rod or wrist pin or whatever.

 

[John Otis]

Good advice about using the broomstick. I have a really long old screwdriver that has been my "stethescope" for years. I had a curious knock once relating to the spark lever that was like the one described. Drove me nuts until I discovered it was end play in the cam. If you take off the oil cap and look in with a flashlight you can see whether it's shucking back and forth while you monkey with the spark and gas. There is an aftermarket shim that will help if that's the source.