My '18 has about 65 hours. Last measured compression was 145 PSI. Been having weird symptoms, and someone said his bike clocks in at 180 PSI... All the best rides of the year are yet to come...so I could not help but pull apart the top end of my bike.
Here are some facts:
Motorex Top Speed 15/50 gear case oil, changed every 10ish hours
Motorex Cross Power @ 60:1 with VP 94 race gas
Twin air filters cleaned just about every ride.
RK Tek head, VForce, Turbinecore 2.1
Tight,slow, singletrack riding, lots of lugging, rarely over 3/4 throttle--or higher than 3rd gear. Lifetime average speed for this bike is 16.1 MPH.
During my trials with the Mikuni, I definitely ran lean at times. Not dangerously, but lean none the less.
Here are my wear findings:
Cylinder still has visible cross hatch, no burns or scoring. Cylinder is still very round, and measures 58.0127 mm which is probably just about the same as it was when new.
My powervalve assembly moves very smoothly, and I have no doubts that it works as engineered.
Piston is a factory size 1 piston, 57.94 spec. Worn piston measured 57.84 at the specified measurement location. Sufficiently beyond the wear spec for this part and justifies replacement. Body and skirts show "polished" areas of wear and look pretty much normal and as expected. Piston is not nearly as "burnt" as it appears in the pics, that black stuff cleans right off revealing metal of uniform heating and color.
No burning or blow by on the rings. Ring end gaps were .55, .56 upper/lower. Wear spec is equal to or less than .40, so again parts are well worn and justify replacement. (my guess is that factory ring gap is around .30 mm?)
Wrist pin bearing is unremarkable, but will be replaced. Wrist pin definitely has some scoring , with corresponding wear in the piston pin bore and boss and will be replaced.
My base gaskets were .40 mm stack from factory.
So that is that... Made it to 65 hours and my top end is bona-fide out of spec, and shows wear to all parts. I will be replacing with a size 2 OEM piston set.
I created a gallery of pics for anyone interested: https://photos.app.goo.gl/jaG7yhgm4b7zNYNZ7