Been trying to diagnose this knock in my 1955 324 Oldsmobile. I think it's in the valve train. But not sure. Took the valley pan off and took a little video. Any help is greatly appreciated.
Pull the valve covers, engine idling take a '006" feeler gauge and slip it under the rocker at the valve stems, one at a time. When you quiet the TAP, (knock is anomatopoeiac) you will have located the lifter/pushrod/rocker/valve guide that is causing the TAP.
Wear some gloves and try carefully pulling one spark plug wire off at a time, if the sound goes away or changes then that will at least tell you what cylinder it's coming from. It sounds more like valvetrain to me as well than it does bottom end.
I tried using the feeler gauge at .006 there was no change. Tried every valve. Gonna try pulling plug wires to try and narrow it down
Might try and put a dial indicator on each rocker arm and see if there's any big difference between the valves. The crazy thing is most of the time it makes the noise in the video and sometimes it make a lower frequency knock. This thing drives me crazy hahaha
Going by the sludge, it sounds about average for a '49-'56 Olds ... the whole valve train rattles, but doesn't ever seem to give trouble unless you decide to clean things up ...