You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: Lower crank case fitment
^It's important that the upper and lower halves of holes like those for the crankshaft exactly match with each other. Normally the manufacturing strategy is to use pins to establish a unique upper/lower fit, then assemble the halves and machine the holes in the assembled parts. The components from different assemblies will fit together slightly differently, which is not good for those critical holes. Your statement "two separate castings that get cleaned-up and machined, then mated to each other during engine assembly" misrepresents what happens, i.e. they actually get mated first, then machined.