Hi Diesel Bombers!

My old 6.2 engine broke and i bought a "rebuilt" engine and swapped it. Everything seemed to be fine except the AC-compressor was siezed, servo pump was broken, thermostat etc. etc. But it was nicely painted...

So when we got it running, it runs great when cold but when reaching temperature it eventuelly stalls after about 20-30 minutes and then it cranks super slow . It is extremely hard to start until cooling down for 30-45 minutes. When the engine is hot the starter can crank it but very slow, and the starter is shielded so it cant be related to heat soaking. The batteries are almost new and tested for capacity and power with good results.

We are 99,9 % sure the engine actually have a LOT of mechanical resistance internally, when its hot we cant move it at all by hand. We have tried removing glow plugs to see if its related to high compression but it seems to not be. When turning it of it also stops instantly, like it is pinching and wont do a single revolution after turning the key off like my old engine did.

So the mechanic who is very experienced (im no mechanic but this seems far fetched) have come to the conclusion, with input from other mechanics specialized in american cars that the only thing left to check is if the connecting rod bearing caps are installed the wrong way.

Ive read everything there is to read about this engine on every forum and this particular problem doesnt seem to be written a lot about. The few ive seen having bearing caps installed wrong have trouble turning it over at all even cold.

So my questions are, do you consider it possible that the bearing caps on the connecting rods could be installed wrong causing these symptoms?

Can you think of any other explanation to this problem?

Thanks a lot in advance for any input!!