Re: Engine knock?

Posted by Mike Flanagan on June 17, 1997 at 18:34:02

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. Knocks are hard to diagnose over the net. From what you describe if retarding the timing seems to help I would first check the timing. With a light. After timing as Henry intended with the engine still on number one TDC make a mark on the crank pully (I use a cold chisel and a light tap with a small hammer then fill the nick with soapstone) now you need a pointer of some sort. I made one that attaches to a timing cover bolt and stays with the car. Align the pointer with the mark on the pully and start the car with the timing light incircuit to number 1 spark plug and the spark lever fully retarded. If you are timing the car correctly (and mistakes are common) the mark and the pointer should be close. You can easily adjust to suit. Next do some research on how much advance you are getting. The timing light will aid in this. Do the math on the circumference of the pully and see how many degrees of advance you are getting. Do the math on the distributer and you will know how much you should be able to get. I have heard 40 degrees but my dist will not travel a full 40 but we run good so Quien Sabe'? Another problem may be in the timing gear itself. If it knocks at idle reverse the timing pointer and push on the gear while engine is running at idle. If knock goes away.... If you remove the head again look at everything for a shiny spot where something may be conflicting. To check for end play on crank with engine idleing have someone cycle the clutch in and out while you watch the crankshaft pully. If the pully moves fore and aft more than any.... At 45 mph you are nearing 2000 rpm so a knock associated with rods or mains would be "loud and often". Sounds like you have a problem not unlike my vibration. Much time, effort and money has been spent and I still vibrate more than the norm. Again, Quien Sabe'?????? I doubt if I've helped you but maybe this will keep you out of trouble for an hour or so.
God speed under 50.
Mike Flanagan, The Model A Fool.

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