91 300zx 5th cyclender knock

ok i have a 91 300zx a mechanic said the lower piston bearing is bad in the 5th cyl. is it possible that the oil pressure
regulator valves could be causing the noise . Because wen i first started it after engine replacement of a used engine it seemed to knock a little but stopped wen fluids circulated. but had a leak coming from the oil filter housing , wen i pulled it of one of the( spring loaded bearings) / oil pressure regulator , fell out an i couldnt put it back in as it should be, but its in might b letting too much or not enough oil thru . could that be the cause of the knock on the fifth cyl. or maybe a vacume line that i missed or put back wrong be the cause .