Part of our discussion was of course about the R50 and cooncat requested an update, so here it is!
I got the crankshaft back from Brent's Motor Works last week. It looks great and was essentially completely rebuilt. gordonmessmer came over and we spent an evening getting the crankcase back together. We were not as well organized this time and had to take the front bearing carrier off an extra time because we forgot the oil pump. We also forgot the oil splash ring so the crank had to come out again. In the end we got it all back together and everything seated properly. I'm glad that I sent the crank out because it's slightly shorter now which keeps the rear slinger from rubbing on the inside of the crankcase.
Then last night I heated up the flywheel (all 12 pounds of steel) and fit it on the end of the crank. The runout is just slightly over the limit at about 0.0045". I'm ready to call that good enough unless there's a fix that doesn't cost too much.
Tonight I sat down with the pistons, cylinders and my set of micrometers. The cylinders are dead on round with no taper. The pistons are as close to the exact same size as makes no difference. The wrist pins are pretty much perfect. The only thing that's possibly out of spec is the piston skirt to cylinder clearance. At the moment it's 0.006". The book says 0.0046" is the max, but I've got it on good authority that the book is being stupid. The pistons are aluminum and the cylinders are steel. It doesn't take too much heating up before you've used up that 0.0046 and are looking at a seized piston. I've got an email out to an expert asking his opinion. If he says they are too loose then I'll find someone to knurl the piston.
Tomorrow I may take the cylinders into a local shop to see about getting them cleaned up. They really need a good blasting and a lick of paint.
Pictures are still on the camera, I'll try to post them soon.