SBC mystery knock

yup

 

had that very same thing in my Nomad years ago---replaced the rod and it went away.

 

well your cheapest fix would be replacing your exhaust gasket! i read the whole thread, and the video really doesnt help much, but change the gasket. they do make crush high temp gaskets, to fill the little imperfections on the exhaust flange. if that does not fix it, then is something else. how about spraying wd 40 on the exhaust manifold to find the leak? i use to do that, it will make bubbles from where its leaking. kinda messy but it does work!

 

ok so if it is the exhast gaket replace it and down the rad you go , but if its still there heres a suggestion that hasnt come up . it sounds to me to be the flexplate hitting the starter gear.. I had 2 motors do it and man i was really pissed ... thought I had a lifter knock too but couldnt find it ... give it a check ya never know ...all you have to do is grind the gear down a bit and it will be gone

 

Here is one that is similar in description ...

only when warmed up, AND with PCV vac***, remove PCV and it goes away !!!

and a short video

 

check for loose bolts connecting pressure plate or torque converter to flywheel. I had them come loose on a car I had and it sounded like a rod.

 

My B-I-L's brother had a '56, 265 that ended up coming apart on the Hwy at 60 mph. He stopped, looked under it, saw the hole in the pan and drove it about 7 miles on home. Never ran again.

It had a cracked piston skirt that finally let go! I saw the hole the next morning!

pdq67

 

Must have been the exhaust gasket. TS didn't report anything further.

 

My noise was a broken fuel pump fulcrum arm spring. Crazy little noise to diagnose.

 

Jimmy G.

Was it present only when warm?
also did the noise go away when PCV was disconnected?