Engine Knock Diagnosis???

brum1

brum1

Well-known member
Been chasing an engine knock and looking for your collective feedback.

Knock is:

somewhat random
heard at low idle
disappears with increase of rpm(or at least greatly minimized)
heard at crusie speed(low level but a more steady knock
not noticed by some experienced Model A owner(or at least stated don't worry about it)
increased with advance of spark
minimized with #2&3 plugs shorted to ground

Knock is not:

Crank pulley-tightened
Timing gear-ckecked with pin
increased in loudness with rpm
floating crank-feels tight
affecting perforamnce- a beautiful running engine

All the research suggest a rod or main bearing; that be said how long can a well maintained Model A engine run without needing to be addressed. Car is driven 35-40 mph but will see a few thousand miles a season.

Assuming a rod or main low level knock; should this be torn down now or can it last for years without adjusting shims?
 
I had pretty much this same symptom on mine. Then one day when I was doing around 50, all h*** broke loose, and you could hear it really good - all the time.
Dropped the pan and discovered that all the babbitt on #1 rod was in the bottom of the pan in itsy bitsy pieces. I don't know if adjusting the shimms when I first heard it would have prevented it, but it could have.
 
Just had a similar issue, after firing up a 29. First 2 hours of warm ups and cool downs for retorque and break in, no unusual noises.
After that a faint low knock could be heard. A couple shake down runs around the block and it became more prominent but not so much when loaded in fact barely heard it at all in third but quite loud when free reving the engine. Shorted all plugs to ground and found it quieted on # 1 and all but eliminated on # 2.
Pulled the pan and found # 2 rod loose on the drivers side nut (the cotter pin saved it from coming right off!) Upon examination the old nuts threads were almost completely stripped. She was just beyond holding 35 Lb.s of torque and let go to settle on the cotter pin for a rest. Removed cap, re-guaged and shimmed, new nut, re-torque, and no more noise! Quite a relief really, as had it let go......well that's another story. My advice? Pull dat pan and have a boo at it before all
H E -doubletoothpicks happens.
Cheers!
 
Drain the oil, pull the pan, go to Harbor Freight for a cheap full face visor. Wait 2 days for most of the oil to drip down. Start checking big ends. Use Reynolds foil method. Take your time if possible when slicing down the shims.

Get it to .015 and you'll be quite content with a very quite engine.

Don't do it and wait for the Babbitt to shred. Very noisy and expensive.
 
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found and fixed my knock by pulling the pan,found #4 Rod was contacting piston Boss,was slightly misaligned when babbit was poured,shaved the piston Boss .030" and has been running quiet and smooth since 1992
 
roccaas said:
drain the oil, pull the pan, go to harbor freight for a cheap full face visor. Wait 2 days for most of the oil to drip down. Start checking big ends. Use reynolds foil method. Take your time if possible when slicing down the shims.

Get it to .015 and you'll be quite content with a very quite engine.

Don't do it and wait for the babbitt to shred. Very noisy and expensive.
Click to expand...
.0015
 
My Dad had a knock and checked all the upper stuff. When he pulled the pan he found the oil pump spring collapsed. The pump was barely being driven and was the source of the noise. I am not sure if this is common but I always reccommend a new spring to anyone putting an engine together.
 
I just completed my 1st shim job on the mains and rods. Do some research and give it a try. It really wasn't that bad. I had a great time (got dirty) and learned a few things. Very satisfying as well.

br,
Tim
 
sounds like mains, they usually knock more with advanced spark, it the knock goes away when shorting out a spark plug think rod, in any case its time to pull the pan and find the problem before you get on real good terms with the guy driving the hook truck
 
Brum, you said you checked the timing gear with the pin, Maybe it is worth taking the timing gear cover off and checking . we had our garage clinic a few months ago and the only way we found the noise was removing the cover and finding a few teeth chewed up on the timing gear.
 
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