I know of an engine that was rebuilt by a reputable professional machine shop. All the right things were done as far as assembly and startup. It ran fine for a few minutes than locked up when shut off and would not turn again.

The reason was seized wrist pins in the pistons. The engine builder said it is a possibility even when you think all the clearances are OK. Sounds to me like things were just a few tenths of a thousandth to tight.

You describe exactly what happened to the engine I saw.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-