Well after taking apart a good running 312 for refresh I find the block is overbored 80 thou and has had a crack repair near number2 main journal ( not into the stud holes) Repair is good and has been fine for the 12 years I have run the car. So, decided to use block and sleeve it back to standard. Ordered loads of new parts at great expense. Everything cleaned, painted and ready to assemble, crank ground, new wrist pin bushes, new everything! First job, fit cam bearings. Went in nice, cam wouldn't even enter. Knocked bearings out, got another set. Fitted middle one first. Great cam goes in nice. Number 4 next......tightened up cam wouldn't go in. Knocked it back out, measured cam bearing bore......oval. Damn. Not an ideal introduction to the joys of building Y blocks.