[Firegoat]

I just drove my 67 Goat home and it ran fine but I noticed a knocking sound at mid to high rpm. It quiets down at low idle and you can only really hear it when you give it gas. If I let the car sit for a little bit you can hear it clang for a few seconds and then it goes away. Just had the heads done, new valves, surfaced and new pushrods. Just dropped the motor a few days ago and it was not rebuilt because the shortblock was still in good shape. Valves needed to be gone through as the engine sat for about 4-5 years. Put break-in lube when it was reassembled. Hope I don't have to pull the motor but was looking for advice or suggestions on what it might be. I know it is not an exhaust leak as I checked for that and have heard them before from my other Pontiac's. Thanks.

[pontiac 455ho]

could be amain bering. or a rod. i last engine blew the front main bearing and it made the same sound. and it got worse when the engine was warmnd up . i got a wood stick put in next to the balencer and heard it and felt it. good luck

[gtome]

I had a rod bearing go that would do that as well. When cold you couldnt hear it at all.

[track73]

When the engine is knocking remove or short out a spark plug wire one at a time . The noise will go away if the offending cylinder has a rod knock. (as the spark plug is shorted out).
I had a Ford 302 that the front main bearing knocked when the vacuum advance was attached directly to manifold vacuum. When I switched to ported vacuum the knock went away.

[Half-Inch Stud]

Me 68GTO has developed the same sort of noise (after having blown the Oil Adapter gasket on the road & emptied the sump & being run-till-it stalled by my brother). Just maybe he left the Switch-Pitch in High stall while the motor was stone cold huh. NO biggie.

I re-flattened the oil adapter & adapter block (long Branch stuff) & it's leak-free. Yet driving reveals a medium rap at high RPM. SOOOOOOOO, when I'm done the 70 Judge re-assy, my 68 GTO goes in the bay for a pan drop and inspect ALL the bearings. Rod uppers & Main Lowers. Luckly I gots a roll of Journal-emory-paper. Just Maybe some upgrades can occur.

[PunchT37]

Being that I can`t hear it, I`d check the work that you did to it first.
How`s the oil pressure? Kinda sounds like a bearing knock. Was the engine doing this before the head work?

[ta man]

Loose convertor bolt?

[Firegoat]

It was a rod bearing. It is at the machine shop and the motor is going for a rebuild. Can't wait to get it back on the road! Thanks for all your help. I tried the spark plug method and it was the #7 cylinder/rod.

[Half-Inch Stud]

Good luck with the Re-Refresh.

I hoped for the converter bolt, but my noise occurs at WOT. Silent at idle and light cruise.

[Fullsize455]

Originally Posted by Firegoat

Valves needed to be gone through as the engine sat for about 4-5 years.

What? Valves don't go bad from sitting. Valve seals might, but the valves themselves certainly would not.