Small Block & Big Block Chevy Specific - crate small block trouble

:bang: I hope someone here can help me. I have a 1984 Pontiac Grand Prix that I put a 305 in 8 years or so ago (from a V-6). last year , while performing a "spirited" start from a stop light the motor started knocking. It was a metallic knock , knock going at engine spped. it would increase and decrease with the rpm. I figured the motor went bad, it did have 167K miles on it. SO I just replaced it with a new 350 crate. new street avenger carb, edlebrock performer intake , hooker headers, MSD ignition and distributor. got it all installed and fired it up yesterday. seems to run real strong. took it for a run up and down the driveway (300 feet) lo and behold this one is making the same knock, exactly. at first it wasn't making the noise , then after going up and down the driveway it started. it is louder that a loose rocker arm or valve. the motor doesn't skip , actually runs great except for this annoying noise. sounds as if a rod is going to come right thru the block. all fresh oil and coolant, etc. good pressure. I mounted it to the same transmission (THM200R4) and only thing I used the same on the motor was the fuel pump. seems to me if it was bearing or rod, the motor would run like crap. I have been working on cars for a while and never heard this noise before on any car never mind 2 small blocks in a row. just don't know where to go after all this work to have the same issue. any suggestions?????
Thanks :bang:

One thing you could do to eliminate the trans is to disconnect the torque converter from the flexplate and see if you still hear the sound. You should be able to push the T/C far enough away from the flywheel to where they don't touch, and the car will still start and run.

I feel your pain. I bought a brand new GM crate motor for my 79 Z28. Not long after startup, I heard a loud squealing metallic sound coming from around or inside the timing cover. Pulled the belts, the noise was still there. I pulled the motor back out, disassembled it completely (to the point of pulling the crank out), and found nothing wrong. Nothing. I put it all back together. No more squeal. :bang: :jest: All that work... and... I just write it off as one of those weird things.

Have you drained and checked the oil for debris?

:bang: we disconnected the torque converter and it is not the trans. i pulled each plug wire one at a time to see if the rapping went away, to try and figure out which cylinder was causing the rapping, there was no change. I pulled the valve covers to see if maybe bent a push rod or broke a rocker but they lok good. possibly a main bearing??????? not sure what is goin on. I have so much time and money into it at this point I am completely frustrated. :engarde:

Check the fuel pump. Sometimes the spring breaks and the pump pushrod floats and bangs the cam.

You sure your timing cover isnt out of whack from the factory? Ive had trouble witha motor that had a slightly bent timing cover and the chain would hit if and make a ticking noise.

Check the clearance from the Timing Gear on the Cam to the oil galley holes. Some times the gear will rub right above the three plugs.