The Stovebolt Site Forums The Shop Area Engine Shop deep sounding clang

Hey all, I am helping my buddy still with the 1953 3/4 ton with the 216. His engine runs smoothly, but has developed a deep sounding knock sound at certain RPM. Its sounds very deep in tone, coming from the middle area of the engine. I am thinking rod bearing-
We went through the valves and the obvious stuff. Could dirty oil cause this noise- I doubt it but thought I would ask here first before taking the pan off and checking the engine. Engine does have tendency to run hot when at speed- and cools off when you slow down. Does not overheat. Main bearings where checked and adjusted in accordance with the shop manual.

Thanks for the help.
Sam

Sam,

A rod, at least to my ear, wouldn't be described as a 'deep' knock while a main bearing would. If it's a rod bearing, you should be able to get it to bang at will.

Revving the engine up and gradually letting the throttle fall will let the rods float for a second and should make any offending rod knock. If the exact cylinder can be found, pulling the plug can sometimes make it knock a bit more steady and pronounced as there is not explosion in that cylinder.

Don't rule out goofy things like a water pump or a generator that's gone south. Use a length of rubber heater hose as a stethoscope to pinpoint the origin of the noise.

Stuart

I would add that a main bearing will knock at low RPM under heavy load.

I'm a little confused- - - -how were the main bearings checked without pulling the oil pan? I'd suggest disconnecting spark plug wires one at a time to try to isolate the noise to a particular cylinder. A severely damaged piston will also cause a noise, but the "clang" description isn't something that's usually associated with internal engine noises.
Jerry

I will, the main bearings were just re-shimmed about 200 miles prior to the new noise- At the time the owner did not have the time to get the rod bearings re-shimmed-

Well I think the plan will be to isolate which cylinder the noise is coming from(I have a stethoscope)

Then to figure out what is happening-


I have ruled out the heavy load- this is when driving around town, on the highway(50 mph), and can even be reproduced when sitting static in the shop while pushing the accelerator.

We will do some investigating and let you know what we find, and I am sure we will have more questions.

ok rods and main bearings check out ok- wrist pins ok

The vacuum advance line is crooked into the advance mechanism. Could vacuum advance problems leak to the knocking sound from pre-ignition, which would also cause the extra heat on the engine when at speed?

Yes. It could cause the timing to be, well, to be too advanced. Hahahaha
I think that this would show up under heavy load, flat out in fourth from 20 mph.

Running hot can be the timing too far advanced.

Have you verified the timing statically? Multi meter across the points, just breaking contact at the mark?

Running lean can cause this too. What about a vacuum leak?

Does this happen right off of idle?

Vacuum leak, just found it. sound is going away quickly now that it is fixed.
Thanks all

Woohooo!
Good to hear!