Have a 2005 EXC. I think it is on its original piston judging from the previous owner he just trail rode with his kids- I have only had it a year and have not put too many miles on it - just 5 enduros and a dozen days out trail riding. After a while the bike got so that the engine produced a loud hiss/whine. No one really could put there finger on it from the outside, and it ran well - but when I stood on my pegs the engine was loud enough that I started wearing ear plugs (it was louder standing up because the loud came from in front of the tank). I always suspected the water pump as it came from the top front of the engine. So today I finally took the top off and sure enough the fan had wore a 1mm groove in the housing. The bearings all feel good - could the impeller/rocker shaft have drifted inwards driving the impeller against the housing?? Any thoughts? Various symptoms the bikes is showing (no idea of hours so could be anything) -more vibrations coming from engine -more backfiring and popping despite setting valves -Engine seems to be running hotter the last few times -no hot spots found in combustion chamber or head - all looked normal -the pump seals were going, some weeping happened when I started the bike in February in the cold -today will not start at all (hence ripping it open) NEVER done that before |I do not have a good history of diagnosing bike problems so I need your help!