ADVISE NEEDED ON ENGINE NOISE

[62_Conv_2-4s]

I have a 327/300 engine in my 1962 impala. The engine runs great and passes a cylinder pressure check and leak down test just fine. The problen is there is a slight knock noise below 700 rpm. You can only here the noise at idle speed. When the engine is reved the knock noise dissapears, It is not valve related as it is a deeper sounding knock. I would like to repair the motor with out doing a total rebuild. I am going to pull the pan and check the main and rod bearings first. Any advise is appreateated as I do not wish to spend a great deal of time or money on an otherwise great running engine.

 

[blkblk63ss]

Check oil pressure at idle might help you isolate the knock. Also after you change oil and filter does any knocking appear louder till oil pressure builds up after starting?

 

[our1962]

Check the fuel pump and rod for the pump, could be worn out but still function's correctly.

 

[64ss409]

I thought I had a rod knock in a 409. It turned out to be the fuel pump. A new one fixed it.

 

[Iowa 409 Guy]

Check the oil filter for debris.

 

[62_Conv_2-4s]

The fuel pump has been replaced but not the rod. I will check the length of the fuel rod and for wear. The oil pressure at idle (650 rpm) with engine warm is 23 psi. when reved it goes to 50. The oil has been changed and a thicker oil was used. It helped a bit but the noise is still there. I did not save the filter so it ended up in the trash.

 

[Don Jacks]

Pull the fuel pump,start the engine and see if the noise is still there.

 

[blkss64]

Does your car have an aluminum case PowerGlide? First, check the torque converter nut & bolts to see if they are loose. Second, check for cracks in the flexplate and then third, look at he face of the converter to see if the flexplate to crank bolts have backed out.
If this all checks out then look at the harmonic balancer and belt pulleys.
Just a few things that come to mind.

 

[blkblk63ss]

Pull one spark plug wire at a time idling on all cylinders see if noise gets less on a certain cylinder. If it does then you have a clue where to look.

 

[DonSSDD]

Take a stethoscope and listen to the fuel pump and each exhaust port. Use a broomstick if you don’t have a stethoscope

 

[62_Conv_2-4s]

Thanks for all the help and suggestions. After pulling the spark plugs one at a time I noticed the noise went away after pulling #2. I'm thinking rod bearing on #2. Going to pull the pan next weekend and check it.

 

[Iowa 409 Guy]

You said the knock goes away on acceleration. If it's a rod it most likely knock more upon deceleration.

 

[62_Conv_2-4s]

You said the knock goes away on acceleration. If it's a rod it most likely knock more upon deceleration.

The noise goes away when free reving the motor in neutal. Cannot hear the knocking noise from the driver seat in idle or driving the car. You can only hear it from under the hood, fully warmed up, and only at idle. No noise when starting it cold. The rear main seal is leaking anyway. I will pull the motor and refresh the gaskets and check for wear while it is out.

 

[1964SuperStocker]

Take a stethoscope and listen to the fuel pump and each exhaust port. Use a broomstick if you don’t have a stethoscope

Stethoscope would be the first and only thing to do. Stop running the engine unless you are testing something. Could be serious, could be nothing but the stethoscope never lies. It will tell you right where the noise is coming from. I use mine so much I just had to buy a new one. LOL!

 

[Phil Reed]

I got mine from Dr. Oz!!!!!!

 

[425/409ER]

Do like other have said and check the fuel pump, if it's ok I am willing to bet the 327 has cracked crank and then do not run it. I had the same noise in the lower end on a SJ 327 back in the 70's and everyone said it was fine just run it. One day I fired it up to leave and BAM it just stopped. We pulled the engine down and sure as all heck the crank broke after the 4th main across to the rod journal. Once you break it the repairs cost a lot more.

 

[region rat]

Thanks for all the help and suggestions. After pulling the spark plugs one at a time I noticed the noise went away after pulling #2. I'm thinking rod bearing on #2. Going to pull the pan next weekend and check it.

It sounds like you have it figured out.
In high school that was the test when you bought a used car.
If the noise goes away, it's that rod.
If it gets louder, bad piston.
Myself I never saw a broken crank in nature. Maybe at the track.
Bob

 

[region rat]

The noise goes away when free reving the motor in neutal. Cannot hear the knocking noise from the driver seat in idle or driving the car. You can only hear it from under the hood, fully warmed up, and only at idle. No noise when starting it cold. The rear main seal is leaking anyway. I will pull the motor and refresh the gaskets and check for wear while it is out.

If something is bad, I probaly have a couple wayward 327's that followed me home.
Bob

 

[Brian64SS]

Thanks for sharing diagnostic tips. The 283 in my 4-door has a rattle like the ball inside a spray paint can that's almost empty. Stethoscope doesn't help me find it. Does a rod knock ever sound that high-pitched? It comes and goes and doesn't seem to related to RPM. Will try the spark plug wire idea.

 

[425/409ER]

Thanks for sharing diagnostic tips. The 283 in my 4-door has a rattle like the ball inside a spray paint can that's almost empty. Stethoscope doesn't help me find it. Does a rod knock ever sound that high-pitched? It comes and goes and doesn't seem to related to RPM. Will try the spark plug wire idea.

Sometimes rod bearings squeak. When I worked a a Pontiac dealer one of the guys that worked next to me had a 3800 Buick engine that we all swore was a rod knock, turned out to be a broken valve spring with the roller lifter bouncing off the cam. They replaced all the related parts and the 3800 was quiet as a mouse.