Motorcycle Repair: top end repair, leak down test, piston

Question
I have a 1988 Honda nx650.I recently overheated engine.I was too low on oil.Now engine makes pinging/knocking noise from top end.I have no loss of power. I assume i warped piston.If so must i rebore cylinder and get oversized piston,or can i just replace with standard size piston  

Answer
Hi michael,
           With low oil i assume there could be a whole lot of problems.Piston yes,crank bearings, valves,cams.You can do a leak down test on the motor to eliminate some of the suspicion,if that is ok then i suggest a tear down to find the problem...glad i could help.