I recently had my boat engine rebuilt at a local but reputable machine shop. Cyl bored,line bored,new pistons,crank turned,new cam etc. Did all the proper break-in procedures. It stared losing oil pressure at idle. Drained oil and found metal. Took engine back to the builder and he found no.2 and 4 mains where toast. He's not sure what caused this. Did I get a bad line bore or did the crank guy f up?