Knocking coming from engine or transmission?

1967GTO

MEMBER
PONTIAC

Pontiac GTO, 1967, newly rebuilt 400 with less than 2000 miles. I was wondering if someone might have any ideas as to a knocking sound coming from the motor. I have not been driving this car as it's in the process of restoration. I have been starting it up to let it run, but that's about it. Hasn't been run on the road for about 2 months, I didn't have any problems until the other day I stated it up, backed it into the driveway and shut it off. Started it back up again, the timing slipped it backfired and a knocking sound started. I reset the timing and checked my carb. The distributor is new and I pulled it to check it, the points are fine, it has no wear. The sound to me seems like it is in the rear of the motor. I checked the flywheel and torque convertor to make sure they are tight and they are. When it's put in gear the knocking gets worse and it stalls out. :Roll: I would be so grateful if somebody might have any other suggestions. Thank you for your help.

1 Reply

HMAC300

MECHANIC
48,601 POSTS

If you have spark plug wire pliers, pull one plug wire at a time while it idles, then reinstall it. If the knock goes away when one wire is pulled that is the cylinder that is giving you the problem. If the torque converter wasn't installed correctly it could have A. Broke th eoil pump gear and that is knocking or B. Spun the bushing in the oil pump. Pontiacs also had a problem with the rear main bearing spinning. If this engine has nver been touched, meaning opened up, then it 's possible it's carbon that has broken off the piston and is hammering between the head. If that's the case GM and FORD have the same spray oil that you sray into a running engine and let sit for abotu 4 hours then start it up and it removes the carbon on the next fire up. Course you need to rev it for a little while to get the carbon out of the cylinders.