One thing that hasn't been mentioned as far as clearances go (C3 or whatever) is that the bearings are fitted with an interference fit when cold (we all know you have to heat the crankcase to remove and fit them). This interference fit (the shrinkage of the crankcase as it cools) squeezes the outer race and reduces the free running clearance. Add to this a tightly fitted crankshaft in the inner race which expands it and the clearance gets even smaller. If you start with too little clearance in the bearing when free it's quite possible to end up with zero (or less) clearance with a cold engine.