Mine was an '86 and it may only be a problem with that year as many engine parts are one year only. I never tore it down as you can't even get head gaskets for these. I did view the carnage with a borescope through the plug hole. First hint of badness was how hard the plug came out and when it did the electrode and ground strap were gone. Looking in with the borescope revealed a piston shattered so bad that the highest up undamaged part was the crankpin. I am assuming either a valve seized in the guide open or valve stem broke
It was a hot day. I was taking a "scenic" route home from work. Had gone about 10 miles and was accelerating out of a long, tight sweeper. It blew top of 4th gear. Left pipe belched smoke, oil, and I actually heard metal tinkling down the road behind me. Engine never stopped running. I pulled over and shut it off, thinking "holy #$%*! Did that just really happen?" Started the bike back up to a terrifying clatter. It even idled! "Ughhh, that ain't gonna make it home 30 miles. Called a ride. The only engine that has ever blown on me of any kind ever. I bought the bike around 2013? with 18,000 on it. I had it for 2 years and put around 10,000 miles on it.