I have a 2012 trx250x and recently when I was riding it loss compression and started singing. Once I stopped it just kept singing in the head, but It regained compression. I took the head and cylinder off it and the piston and rings looked fine but at the top of my cylinder their was a 3mm dark line on the inside. Everything else looks good but should I just bore the cylinder get a new piston and rings or just tear the engine apart to see if anything is messed up in their.