A friend of mine has a 350 with a knock (doesn't sound like a con rod) at idle and when letting off the throttle. If you rev it, it gets louder when you let off the gas, and it goes away when the engine is under load. Sounds like it's coming from number 6 or 8 cylinder. There's no miss in the engine and it has good power. It's not a loose rocker as he's adjusted them several times (hyd cam, stock rockers). I'm afraid of the worst, a wrist pin. Seems like I've heard these symptoms are typical for a wrist pin knock. Any other possibilties? I've also heard a wrist pin knock will go away if you disconnect the plug wire on the offending cylinder. True?

Yes, it's true. It also could be a valve hitting a piston. It depends on the cam and piston size. I had it happen to me. I couldn't hear it at load but at idle with a small amount of RPM's I could hear it. I had to much dome for my C.C. heads.

disconnect the vac advance and see what happens.
Milan

Make sure torque convertor is not loose to the flexplate or flexplate is not broke. I have seen many times a flexplate bolt holes slotted out from being loose. This will make a death rattle that sounds like a bad knock. Mark

Originally posted by Milan:
disconnect the vac advance and see what happens.
Milan He did that and it seemed to reduce it a little but it was still there even at idle in neutral.