HELP! Knocking sound from 390

[NWwildman]

So here is a quick rundown of the engine history/story:
70's 390 4-barrel, older engine that I bought used.  I installed all new gaskets, timing chain/gears, intake, HV oil pump, etc.
Engine has good compression on all cylinders
80lbs oil pressure when cold, 40-60 when warm.

Dropped it into my 64 Galaxie and it fired right up, took for a shakedown run and it runs out nice, idles relatively smooth and cranks right up.

THE NOISE:  Never heard the noise until days after install when I was monkeying with the carburetor linkage... This doesn't sound like a top-end noise to me, I have heard numerous lifter taps, flat lifters etc in FE's and this doesn't sound like that to me.

The noise is a definite knocking sound, BUT it only seems to come on at aaround 2000 RPM when I'm free revving the engine and goes away at idle and goes away at higher RPM..  I'm stumped

I moved the timing around and it doesn't seem to have any effect at all.  The engine runs good, has a little blow-by but nothing crazy. 

Wrist pin comes to mind... but wouldn't a wrist pin be more persistent ??   

[cjshaker]

Sounds like a rod or wrist pin to me, based on the info that you provided. I say that because I've had both issues happen to me in the past and you couldn't hear either until the RPM's were brought up. Typically the wrist pin noise is more prevalent when you decelerate, at least in my experience, but both can be quiet at idle and low RPM and then get noisy as RPM's increases. But having said that, I'd try to eliminate any other possibilities before tearing the engine apart.

[NWwildman]

Yeah, I will poke around and see if there are any other possibilites but it sounds very knock-like... almost reminds me of the GM oddfire V6's when you would get hard on the throttle its like a non-violent knocking that seems to be crank speed...

[jayb]

The fact that it goes away at higher engine speeds is odd.  There's lots of things that can make knocking sounds and fool you.  I had a mechanical fuel pump do that once, and it was still pumping fuel; figured it out by putting a long screwdriver against various parts of the engine and listening at the end like a stethoscope.  When I put it against the fuel pump it was obvious that it was the problem. 

I've also had a header leak that sounded like a rod knock.

Drain the oil and cut the filter apart, spread out the filter material and look for any specs of copper or an abundance of metal particles which would indicate a worn bearing. 

If you don't find anything, pull the valve covers and check that area next, just to be sure that it isn't some oddball noise from the top end.

You can also try adding some heavy straight weight oil, like straight 40W VR1 Valvoline, and see if that quiets it down.  If it does, it probably is a bearing or piston pin.

If all else fails, pull the pan and start wiggling stuff to find the problem...

[Heo]

And you can pull spark plugwires one by one and
see if that change the noise if it does then you
know if its related to a specific cyl and probably
a bearing or wristpin

[NWwildman]

Jayb, I will do a little more poking around and report back.  I moved all of the rods around for side clearance when I had it apart to do the oil pump and gaskets and everything checked out good, also no particles in the pan and the pan was quite clean when I had it off.  I'll get out the stethoscope and see if I can narrow it down better. 

[shady]

I vote for the fuel pump. the return springs break & the push arm will have some free-play that you will swear is a rod knock. The pump will work just fine. As for the spring, it's just laying in the pan not hurting anything.

[machoneman]

On the fuel pump....warm the engine up. Kill it, remove the pump, stuff a rag kinda' shallow into the timing chain cover's hole and fire it back up. It will run for a tad w/o the pump connected.....to see if the noise goes away....or not. 

[WConley]

When you put the new timing chain kit in, was there a separate spacer behind the old cam sprocket?  If you put that back in with the new cam sprocket you may have created the problem.  New cam sprockets have the spacer built-in, so adding the old one on top of that gives your cam huge end play!

I've heard the same type of noise on a newly rebuilt engine, and it was the cam slapping back and forth.  Hopefully it's just the fuel pump like others have mentioned, otherwise the cam lobes and lifters may be all chipped up...

[fekbmax]

Just another thought.
Broken ear on piston skirt, old warn bore and pistons. No load rattle but gets better when it has a load on it.

[cjshaker]

I've had that happen on a fuel pump also, but the sound was pretty constant. I've had rod noises go away at higher RPM's though. I think it was because the rotational speed didn't allow the rod to 'unload', so the noise disappeared. Or sometimes you just can't hear it over the engine noise. But like the others said, LOTS of things can cause a knock. Starting with the filter, like Jay said, would be my first move.

[fryedaddy]

i just had the same problem,turned out to be a hole in my header.i would have swore it was a knock

[fastback 427]

Havn't seen it mentioned above, but have you checked for exhaust clearance? Had a pipe touching a crossmember once did about the same thing.

[NWwildman]

i just had the same problem,turned out to be a hole in my header.i would have swore it was a knock

Ok, I'm not saying its cured BUT I re-torqued the manifolds and replaced the steel donuts(new) with new fiber donuts because I was suspicious of the seal I was getting.  Aaaaannnnnddd I drove it about a mile last night and the engine is so quiet at idle or light throttle I can't tell its running other than the song from the pipes.  Under hard throttle no noise, light free-revving no noise.    

what the heck!?  it knocking like crazy a day ago when I free-revved it.... I will keep everyone in the loop as I investigate but I'm starting to think it was a weird case of resonation/leak or something along those lines..
Engine was still holding 70lbs oil pressure cruising at low rpm

FE's never stop surprising me

[NWwildman]

It's BACK!

So here is the exact circumstances where the noise is present.

Oil pressure stats:

cold 600 rpm 75-80 PSI
Cold rev 2000 rpm 75-80 PSI

Warm/hot idle 25 PSI
Warm/hot cruise/rev 45-60 PSI

The car will make a slight knock very quickly when it first fires after sitting for a while

The engine is silent when cold and oil pressure is high, revving, idling etc.

Once the engine is warm it knocks like wild when revved beyond 2000 rpm and rattles as it slows down then gets quiet once it hits idle speed.

Engine is whisper quiet at cruising speeds (so quiet that you'd think it died) but if you hammer on it and wind it up it will knock like mad at higher RPM but never loses power.

The engine does NOT smoke, burn oil or misbehave any other way.  There is some blowby that is consistent warm or cold.

Then engine runs strong and can get rubber from a stop (good for a bone-stocker) but the noise is bad and I know something is angry in the engine... Tried a stethoscope but cannot narrow it down to a certain area very well, tried a broom handle as well but no luck.

Could this be valve springs causing all the commotion?  I know that they were rather weak when I had the engine on the stand but since it keeps pulling at higher RPM is just doesn't feel like valve float but ??    Stumped!