Here's the background on this bike, it's a friends machine and he got it from another friend of mine so I know it's history for at least the last 4 years. It was ridden mostly in the desert, a few times at the track and a few times in single track/technical stuff. It's always been a good running machine, one or two kicks usually got it going. The current owner let it sit for half a year while on a deployment and it wasn't running well. We cleaned the carb with minimal change, and after a second more thorough cleaning we got it running great again. He brought it out to the desert two weeks ago and joined my family on a 40 mile loop. We weren't riding fast, lots of stopping due to wife and kids. The bike was starting and running great. As we got close to camp, he and I took off across a dry lake bed since we could open it up a bit. His bike has a bit of an edge on my WR400 so he got a good jump and then I noticed that he slowed down and I blew by him. He said the bike just felt like it ran out of gas, luckily rolled right up to camp. We both looked it over and it had very little compression. When it cooled down, we pulled the valve cover and there were no tight valves. I knew there were problems with the piston or rings so we packed it up and brought it home. Later in the week when we took it apart this is what we found. The valves look okay, some small sprinkles of aluminum on them but otherwise decent. What would cause the piston to do this? Was it just it's time to go? It may be the original, I'm not certain. Anyway, we just wanted to know if there was something to look into that may have caused it prior to rebuilding and having the same thing happen again.