The engine machinist had a polished my crankshaft, when I took the pistons in for my rebore I had a look at the crank, he said the journals are a good size and they where all good but there was 1 main bearing journal in the centre of the crank that had a slight score that I could feel with my nails, he said I could just put shells in or he could regrind for £70, not sure what to do, how bad do they normally have to be before they cause a problem?

if its in the center its running on the oil groove, so just polish it as smooth as possible ie its not got raised egdes

Yes James it in the center of the bearing where the oil runs, slight edge but not that bad, strange how all the others are perfect

i wouldnt worry then