I have built somewhere around 20 686's for raptor's, rihno's and grizz. We have not seen any problems with them yet. Best info I can offer is, Trinity racing offers the kit. comes with a new cylinder measured and matched piston and rings, And cam of your choosing. Then you send your cylinder back to them for a core. Make sure the person installing it knows about overhead cams. If I can help anymore give me a shout
Thanks:
Chris Hanson
Redline Offroad & Performance
780-207-9995