clack/ knock noise

POPGUN

Member
1941 JD A - could a worn main bearing make a clacking/knock noise at idle and go away on acceleration. If so is it an in frame fix.
 
Have you looked at the clutch lately? They can make some noise also, just remove the cover and look at the splines.
 
Pretty open question, yes I read the whole post :arrow:

Take a large screwdriver or length of tubing and put one end up to your ear and move it around until the knock is the loudest, heck I've had a slick spot on a fanbelt "clack"
 
Very hard to tell what noise is what especially on the internet.
I can help at least by telling of some of the things I have found in past JD A projects.
loose flywheels and clutch drivers run rampant on those.
Cam bearings mainly the LH side are usually found in bad shape.
Some of those early ones have bronze wrist pin bushings that can come loose.
I had one with an insert rod that was tap tap tapping on the top side of the crankcase and needed some grinding so it went away.
I had a B with insert rod bearings have a rod journal make a noise it was only like .001 or maybe .002 but not any more than that out.
Easy enough if you have shimmed babbit rod bearings to check and readjust them.
Main bearings are a lot harder to get at. You can put a dial indicator on the end of the crankshaft and pry up and down and see how far out they are.
Many of these things I found were from poking around looking for problems often times more than from a certain noise. The cam bearing was a tough one on my first one I found it on. It had running issues that would come and go and didn't really make any noises.
 
Hello Popgun,

Usually if the sound changes with R.P.M's is not the cranckshaft. A worn wrist pin or piston slap, acts like that changing sound as the rpms change. That is my guess.....

Guido.
 
Badly worn main bearings on my 50 made a heavy worrisome thumping noise when in a hard pull at about half throttle. No noise at any engine speed when not under load. When I took the clutch pulley off, I could lift the end of the crankshaft by hand and duplicate the thumping noise.
 
Done the breaker bar stethoscope, but its obvious without it its in the sump area. Did flywheel deal nothing there. Its a ball peen sound at low rpm and leaves at higher rpms.
 
Years ago at a sale my dad bought a very straight 8N with all new tires for $800 it had a knock in
it turns out it was the fan belt slapping. Made his day.
 
Could have scored pistons if its been re-bored and had aluminum pistons put in. Pull one plug wire at a time with it running if knock goes away you have a scored piston on that piston. If not I bought a 49A with a knock in it, flywheel, clutch driver wrist pins all good, it had been overhauled but they did not remove the ridge at the top of the cylinder bore, new rings weren't worn and were hitting ridge, knock, knock, knock.
 

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