Now this post I can speak the voice of experience. hahahah :confused:

I have a '54 235 full pressure. One day out of the blue it started knocking. Loudest at idle, and even louder when the clutch pedal pushed in. Oil pressure was 20 PSI at idle hot. Motor still ran smooth and had power. First I thought it was the clutch, then I thought it was a rod. Turned out to be the #3 thrust main brng had taken a beating.

I pulled the engine and disassembled. Lots of things wrong that changing the crank bearings couldn't fix alone.

Check crank end-play with a dial indicator watching the flywheel. If runout exceeds .010" the thrust main is shot. And Chevyman is right. When a crank main goes, so goes the engine. If the mechanic says to change the mains, its time for a complete engine teardown and rebuild.

Get a second opinion from a shop that knows old engines. See what their diagnosis is, and how much the cost.

"Patching" an engine's bearings instead of a rebuild is usually a losing proposition in the long run. You may fix whats making the noise, but the rest of the motor is prolly worn out/damaged anyway.

Happy trails

Chip

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes