At 86.5 MM the liner is bound to be thin. A suggestion or two. First run 32:1 fuel/oil ratio. Second,run race fuel. Not necessarily high octane but a good leaded fuel. I like the VP U4 series. My YZ is only on the second oversize and when I rebuilt the crank it was only to balance but if it's in my hands it gets new bearings. There's much to be said for good fuel and I'm sure much will be said.