Just bought a 87 GTA for a parts car. Mainly bought it for the new tranny that was recently installed and the disc brake 9-bolt rear end.
The eng (TPI 350) is making a loud knocking sound.
While at idle, it's intermittent; but more knock than quiet.
Knocks the same when cold and warm.
When it's rapped a little (1500 rpms), it sounds really bad.
Putting tranny in drive doesn't seem to make much difference.
All cyls seem to be firing, runs smooth and has lots of torque.
Sounds like the bottom end, but I'm not sure.
Does a bad main bearing make a specific type of sound?
I've heard that a lower rod bearing will make a double knock sound and that's not what I'm hearing.
Kinda sounds like someone's inside with a hammer striking at random intervals.
I've pulled the tranny, and checked the flywheel.
Torque converter bolts were found to be tight.
Eng turns over easy. (I was able to turn it over by hand while removing the torque conv bolts)

Has anyone heard this type of knock before?

 

i had the same noise coming from my L98 in the ROC. i have the engine on the stand and it is a spun rod bearing. don't drive it as is it or you will destroy the crank. maybe it's already beyond repair?

 

Does it have oil pressure? (25 lbs hot idle, 50-55 hot cruising) If it does, the bearings are OK.

I'd suspect a cracked flex plate.

 

strange thing is mine had pressure too 30psi ..... it was knocking and then it went away. the next day it was knocking like a @#$#@%#$%^$.

 

An uneven knock could be a loose piston pin, cracked piston,
cracked flexplate, broken weld between flexplate and ring gear.
(hard to see sometimes).
Try disconnecting one spark plug at a time to see if it is one particular cylinder knocking {rod,pin,piston} or external
{flywheel} or even a broken fan belt pulley.
Some times exhaust leaks can sound a lot like engine knocking.
(collector flange gasket)

 

Thx for all the replys!

The knock is very metalic sounding,and very loud.
You can hear it from 50 yards away with eng idling!!
When probed with a stethoscope (actually a big screwdriver), I hear a louder knock when sampling the left valve cover as opposed to the right. Something in the valve train maybe.

Ocassionally, the motor will stumble when it knocks. There's some kind of binding going on in there.

When you guys refer to the flexplate, it that the same as the flywheel?
The flywheel looked OK when I pulled the tranny.

It's definately not an exhaust leak; they usually get louder when throttle is advanced. I have heard a few that did sound a lot like a knock though. (I worked at a muffler shop as a youngster)

I'll do some more poking around next week; eliminating cyls, and etc.
I'll let you guys know what I find.

At least the tranny swap is going good..
Made my first test-drive abt an hour ago..
The OD is sweet!