The Stovebolt Site Forums The Shop Area Engine Shop Lower end clunking noise

Did some searching and reading and I think I may have main bearing issues, but I wanted to run it by you guys first and see if anyone had any additional insight.

Just recently, our full-pressue 235 (from a '55 car, in a '54 3600) developed a low-pitched "clunk" in the lower end. I used the old stethoscope/rubber hose trick and determined it was coming from behind the oil pan or the lower end of the block. It's a really subtle clunk or tumbling sound. It only does it at low idle. Giving it any throttle makes it disappear. It doesn't have any discernible pattern and isn't consistent like a rod slap or other knocks.

So, main bearings? If so, what sort of R&R can be done with the engine in the truck? Can I pull the oil pan and do an inspection on the bearings?

I know the right answer is to pull and rebuild the motor, but I'm not wanting to drop $2500 on it right now. We don't drive it a whole lot, so if there is anything we can do to patch it together for another couple of years or until I can find another 235, that would be helpful. Thanks!

Hy chicklin, any idea what the oil pressure is when the engine is making this noise?

You can pull the pan and inspect the bearings without removing the engine. I would suggest you get a service manual for your engine, and do some reading. That should describe what you are looking for - along with the necessary specifications. Good luck with your project !!

Steady at 30 PSI, hot idle. Compression is about 130 psi across the board, vacuum gauge is steady at 19 lbs.

I've got the factory service manual, so I'll take a look.

If you can make the noise go away or change note noticeably by disconnecting spark plug wires one at a time, you've probably got piston slap, not a bearing problem. One or more pistons might have excessive skirt clearance, and is rocking in the bore as the spark plug fires. If that's what's happening, it's mostly just annoying, not an impending disaster.
Jerry

I experienced the same sound out of my 216 a coupla years ago. Clunk sound at the lower part of engine at idle and disappear when the engine revved up. It was a bad harmonic balancer. Any rod or main bearing noise, and piston slap I experienced with other engines always got louder when revved up.

Good idea....how were you able to diagnose it? Will it have some play if I grab it and wiggle it with the engine stopped?

I found it by accident. I took the fan belt off. Started the engine and the noise was still there. So, it wasn't the generator or the water pump. Shut the engine off and grabbed the harmonic balancer, it moved and made the clunk sound I had been hearing. Without removing the radiator I was able to get the harmonic off with a harmonic puller. Pushed the new one on by using a very long 1/2" extension through the grill crankhole, and a large socket against the harmonic balancer. I had lucked out and the front end of the crankshaft was not damaged.

You might check the clutch/throwout bearing, also.

cm

Noise does not seem to change whether the clutch is in or out, so I'm leaning away from throwout bearing issues.

Do not disregard the possibility of loose flywheel bolts (slightly,not very).This happens often when someone has left out the dowel when reinstalling the flywheel and crank grinders love to lose the dowel so it is forgotten on reassembly.
Get a bar on the flywheel rim and test for slack in the FW/crank/balancer assembly.
Or just wait---like pregnancy it will show itself clearly in time.

I second looking at fly wheel bolts. I had the bolts loosen one time on my truck. Clunked at idle, but would clear up at idle.

I believe with a main bearing knock, it will get louder as you load it up with the clutch. You could do this with the parking brake on using a low RPM.