Knocking coming from the engine.

solved

 

If its not the converter or the flexplate then theres only one spot left to check really. Pull the pan down and start checking rod bearings.

 

If it were the rod bearings wouldn't it get worse when I accelerate? The knocking goes away when I give it gas then comes back after a few seconds.

 

I'd quit running it and check the bearings before I knocked them all out.

 

Cracked flex plate.

 

Just a long shot but is it getting hot? Had the same problem in my 56 Pontiac with a 350. Turned out it was a head gasket right between 3 and 5 cylinder. Gas was getting through and detonating in both cylinders---NASTY!!! Just my 2 cents!! Do a compression check.

 

Hey Nerd, if that is a chevy engine it might have a broken crank shaft. I've personnally seen two cranks break right behind where the timing gear presses on. the engines ran fine but had a bad knock. Grab the balancer and see if you can move it at all, if it has any play , that could be your culprit. I have no idea what caused it on the two I saw, they were stock engines in daily drivers. Maybe GM cheaped out in the late 70's early 80's on their cast cranks. Happy hunting, Mitch.

 

If the engine was just installed it could be that the engine sat on the ground and the pan is bent just a little and hitting the crank.

 

Nah, the engine was put in about 10 years ago. I just noticed it yesterday.

It's not the a cracked flex plate, already ran a compression test, pulled the plugs and didn't see any difference...

It runs fine, doesn't get hot. Just sounds awful.

When I'm going down the road and accelerating, the knock disappears....ugh.

 

Try unplugging your vacuum advance.

 

A knock coming from the rear of the engine only at idle when not moving, eh? And just noticed it too. Is the knock crankshaft speed or camshaft speed (fast or slow)? Warm or cold? Automatic or manual transmission? Does it get worse when you put it into gear? Solid engine mounts or rubber? Headers or manifolds? Is the oil pressure OK?

 

Just checked out your photo album, cool car (except Pontiacs should have Pontiac spark plugs ). How are the engine and transmission mounted? Like a '57 Chevy w/front engine mounts and bellhousing mounts?

 

The knock seems like a real noisy lifter towards the rear of the engine but goes away when accelerating. The only reason I asked about the engine and transmission mounts is because I've seen bellhousings crack when using the old SBC front engine mounts with a latemodel transmission mount. All the valves are opening and closing the same, no wiped lobes, no egged out guides, good compression. Exhaust rattle? Is the heat riser valve still in the exhaust manifold? Got a stethoscope?

 

A stethoscope can be a big time saver. You'll really know it when you hear it! I've seen oldtimers use a big long screwdriver like a stethoscope too. Putting the vehicle on a lift to allow you to safely get under it while its running might help also.
Good luck

 

check your flex plate very close with a 250w worklight. did 2 for people that swore they were ok. if your oil psi stays up its not bearings. your convertor could have a few loose fins as they are only tack welded from gm.

 

It's mad because it doesn't have a Pontiac engine in it anymore.


On a serious note, my daily was kind of ticking/rattling at idle the other day after I drove it 2 hours straight. I was worried for a second before I remembered that I bent some of the heat shields on the manifolds around while I changed the plugs out the night before, and it dawned on me that one of them must be loose enough to flop and tick on the manifold somewhere. It's not something dumb like that on yours is it?

 

you might want to pull the torque converter back away from the flex plate and check the flexplate bolts for tight also check the flex plate for cracks between the webs.

 

Several have pointed to the flexplate and I cannot disagree. I had a reman crate in my 39 chevy, same sound. Thought it was the crank, but the only part I applied was the flexplate. Pulled the*******, re tourqed the flywheel bolts,****embled, problem gone.

This doesnt mean NOT to perform the other checks, even the pulling the pan to take a peak. But since its in the rear, I think of my only experience with that sound.

Post your findings!

 

Sounds like you need to rebuild your motor.

 

What was the verdict? I have a similar issue. A fresh rebuilt SBC 350, Rear bottom end knock, checked bearings on the main and con rods, no issues, 80psi oil pressure, wrist pins seem ok, separated trans from engine all is good. Maybe too much oil pressure??? Has a hi volume oil pump.

 

If the crankshaft is broken right there,what is turning the camshaft? Or do you mean the crank snout beyond the cam sprocket is snapped off?

 

It's a guessing game, if the engine's been in the car for 10 years, maybe it's time to pull it out and invest in a rebuild. To keep driving it is only asking for more damage, knocking sound, metal against metal is never a good thing and something that just magically goes away!

What matters is what is going on inside your powerplant, not the "what ifs" here. Good luck with the ol' girl.

 

Still, the way you describe it, it sounds like a cracked flexplate. The crack is almost impossible to see with the trans and converter still in place. Good luck with it man.
JM$.02

 

OK, pull the flex plate and go from there.

 

YA its mad at you, engines don't just knock there is a problem inside that needs to be dealt with no snake oil fix here just take it out and rebuild it,,,

 

If it has headers my bet is a blown header gasket. Had a similar knock on an engine at idle speed that turned out to be a blown gasket.

 

It takes a trained ear...

 

put it in drive press the brake hard and goose the gas if its a crck in the flex plate it will make a loud clicking sound. had the same problem with a mack one and a xj6 jag

 

Couldn't you, for free, crawl under, unbolt the flexplate to converter bolts, then start the motor and see if the knock is still there? You'd have to be able to push the converter back a bit I think. Either it will still knock or it won't, but you can bolt it back up and still drive if you don't have the beans to repair it.

 

This was the exact advice I was gonna offer.

I've run into a couple cracked flexplates that you just couldn't see with everything****embled. One of em was diagnosed by a professional mechanic as a fatal engine knock and we only found the bad plate when removing the engine, new one purchased and on the stand

When inspecting......things are oily and dirty, and oil has a tendency to streak a flexplate. A crack looks EXACTLY like an oil streak to the untrained eye. Consider shooting a bunch of degreaser in there followed by water, let it dry, then inspect.

Good luck