I've resolved the next step in my refurbishment of the R90/6 with the bad cylinder. This motor has R90 cylinders, bored out to fit R100 pistons,but with stock R90 heads. I found a nice set of R90 cylinders so I can start over. So...I could go one of two ways with this. Have the new set of R90 cyl's bored one over, and put new pistons in it. About $750 total cost, sticking with the R90 setup. Or -- have the R90 cyl's bored to accept the R100 (93.97) pistons that I already have. About $250 total cost. More low-end grunt, which is where I like to ride. Obviously, I'd like to spend less. But is it a good idea to do that overbore? The machinist is quite experienced with airheads and says he can do it. I googled the topic and there are some folks who have run 100s with R90 heads. But, the ones I found were cylinder swaps, not big-bore treatments. Can the R90 cylinder be safely bored out that far?