Engine rebuild

[Peterfour]

I have rebuilt my ej25 4 times down to main bearings. I have blown my main bearings 3 times in my driveway on the startup. 3rd time I replaced my oil pump (Should have replaced it first thing). I am at a crux. I can only think of oil journal clog (don’t think there is one) or improper main bearings clearance. Crankshaft is new but has been polished a few times. My only thought is I did not measure clearance because I thought it was a relatively new crankshaft and did not need to. I desperately need competent advice.