Re: Engine knock?

Posted by Jim McPherson on June 17, 1997 at 22:56:27

In Reply to: Engine knock?
posted by Gary Rudicil on June 17, 1997 at 15:44:07

: I've had a problem in my 1929 Model A engine ever since it was overhauled back in the early 1980s.I tore the engine down and had the cylinders bored to .100 (due to damage from a broken piston wrist pin lock).The mains were repoured and align bored, the block was decked, and the head resurfaced.The pistons are new, the piston rod bearings were also repoured, with new wrist pin busings installed.It has a reground camshaft and .003 oversize cam gear (since I used the original crank gear which looked okay).When the engine is run cold at 35-40 mph at full distributor advance, the engine is quiet.However, once it warms up, it begin a very noticable, deep knock.Retarding the spark half way helps, but doesn't completely eliminate the knock.I've rechecked the clearances of the main and rod bearings twice, and even installed an oversize headgasket, thinking maybe a piston was hitting the gasket.That made no difference.About the only thing I can think causing this knock is either the head has been resurfaced too much, and a piston is striking the head (but I didn't notice any sign of that when I installed the new head gasket).The only other thing I can think of is maybe too much front-to-back crankshaft motion.I didn't think to check that with a feeler guage the last time I had the oil pan off.
: If anyone has some thoughts on this, or similar experiences, please let me know.I've never heard a similar knock in any other A I've encountered, and I'm definitely baffled!
: Thanks.
: Gary Rudicil.
Gary,
Mike gave you some good advice. I just rebuilt the engine in my "A" but had it sleeved to standard. When I got through setting all the clearances and went back to torque everything and install cotter pins, the engine was so tight I could not turn it with a 3 foot wrench! I finally got it to turn by pulling on the wrench and bumping with the starter. Finally I set the timing this way and started the engine the same way. IT had the same knock with the spark advanced and it reduced in sound or went away on retard. A fellow Model A Club member thought I had the timing advanced by as much as 20 degrees. I knew from the way I was forced to set the timing that it was advanced, I could see the piston was on the down stroke (well that would be retarded, correct?). Anyway he kept adjusting the timing by moving the distributor cam and the knock went away. One additional thought. If you don't have a timing light you can check when the points are open or closed by using a volt meter across the points. Let us know what you find. Good Luck, Jim McPherson

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