Engine is in a 1955 Super 88. It's a 324, the car is all original and has 90K miles. The engine runs fine and has no issues other than this knock, knock at low rpm and/or coming off a higher rpm. The oil pressure is really good almost 30psi at idle and 45psi while driving. You don't really feel anything and when I check with a stethoscope it sounds fine like a clock running. The knock goes away after the engine is rev'd up and while driving you don't notice it. I removed the belt to remove the water pump and generator from the equation and the knock is still there. Could it be the balancer or do you think it's bearings? Could maybe be pistons too, they had a factory defect didnt they? Can do a Youtube video if it comes to that.

 

Pointless for us to speculate. Sounds like you've got it narrowed down pretty well. Make sure torque converter bolts are not loose.

 

Its forward on the engine not back by trans. There would only 30 bolts to check, lol.

 

Whats up front...timing chain & fuel pump.
Is it upper tick tick or lower thunk thunk.
Oil filter have metal in it?

 

Using proper insulated spark plug boot pliers, disconnect one spark plug cable at a time to see if it changes the sound.

 

FWIW, there are many articles regarding rocker assembly noises on these early Oldsmobile 324 engines.
Example:
https://www.jalopyjournal.com/forum/...4-olds.622303/

 

If the noise is lessened (even goes away) when the engine warms up, it does speak to the possibility of lubrication since any oil will be far more viscous at lower temperature than higher temperature.

 

Here is an issue, problem that hasn't come up in a while, sounds like a wrist pin knock, doesn't happen often, but this description reminds me of it....Tedd

 

Tedd, Was wondering the same...to the OP a wrist pin has a unique noise when it is loose. It makes a "double" click or knock as the piston goes up and down near TDC. They usually are louder cold and quiet some as the engine warms and the piston expands.

 

Lower, oil filter is clean. I am going to remove the belt again and really study this more. Also, taking to my buddies tomorrow for another set of eyes and ears.

 

Tedd, seem like a piston, agree. Will get another opinion tomorrow. My buddy has rebuilt many 303s and 324s, he is an aircraft mechanic also. We will see what he thinks.

 

It's definitely not a top end valve train noise. The engine sounds really good with a stethoscope. Too bad I don't have a way to record a WAV file to share the sound.

 

Start simple working towards engine tear down inspection.
Pull the fuel pump and look at the arm and eccentric.

 

Not as a fix, but to help you diagnose the problem, try and add a jug of STP after the engine is warm and see if it quiets down. A higher viscosity oil may let that piston float a little quieter on the wrist pin.

Should it turn out to be a wrist pin, they will usually last a long time before give you any bad trouble. The problem with that is you will have to listen to the damn thing every time you are sitting at an idle...Tedd

 

We don't think i'ts a piston now. Rod bearings, we removed the belt and ran it for a awhile, it does have a knock as it revs up. We think its a few rod bearings, probably #1 & 2. Another issue is there is #7 cylinder head on the driver's side and #8 on the passenger side. So it's been apart before. No idea on the history of that but the compression difference between the heads probably didn't help with the longevity of the motor. It's got 92K on it now. I will posting a new thread regarding replacing with another 324, possibly a 1956.