ya i have a 1985 kx 80 also,it looked like the big end bearing on the crankshaft went out allowing the piston to move an eighth of an inch higher and one of the ports snagged the piston ring,causing it to bend and score up the cylinder verry bad,check your big end bearing before running it with the new top end,if it was me i would replace the big end bearing anyway,just to be on the safe side
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