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Old 05-14-2012, 07:14 PM   #1
DiabloADV OP
Joined: Oct 2010
Location: Nor Cal, USA
Oddometer: 2,336
Next bit of advice -- Big Bore or Stock?

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?
1974 R90/6 motor w/1050 kit; twin plugged; installed in...1970 R60/5 frame; RM125 front end; KZ1000 Police Tank.
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