what will cause a fresh re-built engine to spinn a connecting bearings?

Question

i had a renault 10 tons truck engine rebuilt , and it spin # 2 bearings , it was polished and re-installed , only to have #3 spin this time , new pistons and sleves, head and all connecting , and main bearing ,it was torque ,and all lifters was set . , now i am thinking of replacing the engine for a mack 250 , i have now in it a renault 711 i 6 cylinder.if any one have a mack 250 for sale let me know ps , thanks for your help

Answer 1

A few things could have caused the problems you are experiencing.
1. The rebuilder did not prime the oil system. This will cause the engine to run dry without oil pressure for a few seconds at startup and may create instant damage to the bearings
2. There may be a problem with the oil pump causing low oil pressure. If you have a gauge or light this should be an obvious cause.
3. The new bearing clearances are way too tight. If the bearing to crank clearances are too tight, the oil film will not be sufficient to prevent damage.
4. Metal debris was left in the engine after rebuild.
5. The engine was operated too hard after initial startup. I doubt this reason as it sounded like the issue happened very quickly after startup.
6. The engine oil cooler was not cleaned of metal debris or replaced. I don't know why the engine was replaced but if the previous engine had a major failure, then metal particles could be left in the oil cooler system.

Answer 2

Improper clearance on the connecting rod bearings. During installation you should have used Plasti-Guage to set the proper clearance.

Answer 3

Someone was sleeping at the switch on this rebuild. Don't have the same person rebuild the Mach engine when that time comes.