rhoeven

I need some help.
My automatic '81 developped an intermittent knocking sound during idle and only when warmed up.. It seems to come from the rear of the engine block.
The car idles fine at 650rpm, oil pressure is about 50 psi.
The knocking sound has an irregular pattern , sometimes disappears alltogether for approx. 5 secs and it always disappears as soon I start to drive.
I noticed that I have a small engine oil leak at the rear of the block. (oil drip through the torque converter cover plate)
I'm not that worried about the leak but I'm concerned about the knock.
What can it be?
I purchased the car almost 3 years ago with 59000 miles and has now 77K on odometer but I have no idea about the real mileage.
The engine runs great and does not burn any oil. Also all smog equipment is installed and functional.
The transmission is a new 4 speed TH400 with approx 5000 miles

Any advice is appreciated.

Roger
:cheers:

BB wowbagger

...Could be a bad hyd lifter.. :smash: :cheers:

Larry B.

What you are hearing sounds very much like a worn rear main bearing. I know that's not what you wanted to hear but... the noise and the leak sure make a good case for it. Try running a higher weight of oil like 20W50. If thicker oil helps or corrects it then that is most likely the culprit.

vettfixr

Before you start tearing the engine apart make sure it's the engine that's causing the problem. It could also be something loose in the exhaust system. The pipes go through the crossmember not too far behind the rear of the engine so a loose pipe or a pipe that's hitting the floorboard or something else can sound very much like an engine knock in the rear of the engine. Might be worth taking a look. Also, about the leak. I thought I had a bad rear main seal because of oil that dripped from the flywheel cover on my 4 speed. It turned out to be a leak from the valve cover gasket that worked it's way down the back of the engine. Take a look here too before major surgery.


[Modified by vettfixr, 9:39 AM 8/1/2003]

Dalannex

Is it a knock, or more of a tick????? Could be a lifter, or an exhaust leak if it's kind of a tick sound.

-Justin

Ki m Le

Sounds like your heat riser valve! Disconnect and plug the vacuum hose feeds to the heat riser valve on the pass. side exhaust manifold to see if the noise goes away.

rhoeven

It is a knock similar as if one crankshaft bearing went out, no tick.
If it were a crankshaft bearing, I would think that the knock is very regular and dependent of the engine rpm. The noise I have is very irregular and only during idling on hot engine.

Oh, I must correct my initial post regarding the transmission. It is a 700R4 instead of TH400 but I think this is not related to my problem.

Bluevetteman: I already run 10W40 synthetic.

Rear main bearing makes a lot of sense, specially with the leak but I still don't get it why the noise is only there during hot idle.
Do I have to pull and tear apart the engine in order to fix this?

Thanks keep em coming.
Roger



[Modified by rhoeven, 12:51 PM 8/1/2003]

Kevin_73

Maybe not. While I was investigating a knock in my engine several people suggested that I check the flywheel and torque converter bolts, apparently if they are loose they can cause strange knocking sounds like you are describing.
This did not turn out to be my problem, but maybe that is what is going on with yours.

rhoeven

This makes a lot of sense since I had engine and tranny out about 2 years ago :eek:
I'll check it out this weekend.
Thanks for the tip.

Roger

Larry B.

Typically a rear main sounds like a low dull rap and they will do this as soon as the bearing clearance gets more than the oil can fill. They do usually only make noise at warm idle with no load on the engine. (oil is thicker when cold.) Heres's a test to try... When the engine is cold listen very carefully imediately after it starts.. (like the first two or three seconds before the oil starts circulating) if you hear the rapping noise and then it goes away until the engine is warm. .. that is a good indication of the rear main. You can fix it by pulling the pan and rear cap. Not real tough. It just takes a little finnesse. Hopefully the crank is good. BUT.... if it is a bearing and you keep driving it, it can get worse and damage the crank. I do advise checking all of the thing others posted about as a precaution. It's a hard call diagnosing without actually hearing the engine.

Steve81

:iagree: I had this same problem a while back and that's what it was.

Jvette73

Ill jump on the band wagon to check convertor bolts and for possible cracked flexplate. Ive personally heard this knocking caused by loose and or missing convertor bolts on at least 2 different cars. When I heard it the sound would kinda go away when you increased the rpms, but as you let it slow back down again it would knock knock knock. And then intermitintly knock while idleing.

munday

You can check easily to see if it is a main bearing, I learned this from some fiat guys, and it works on an inline for so i guess it would work twice as good on a v8 :)

on the inline four you just removed spark plug wires 1 at a time until the noise died down, if it did, it was that main bearing the the cylinders pistion ran too. so i guess on a v8 without too high of compression it would work removing 2 plugs at a time? what do yall think?