Hi, I recently bought a non-running 2000 Yamaha XL800 that has 47 hours on it. The previous owner said it began to run bad and he shut it down. The waverunner is in very good shape other than the engine. I did a compression test and the Mag cylinder is 120 psi and the PTO cylinder is 90 psi. I took the head off and the PTO piston is beginning to show signs of melting on the exhaust side. The previous owner must have had a plugged carb and run it lean. Luckily for me, the cylinder walls are still perfect, no scratches or damage. The head has a couple aluminum specks on it, but it is basically perfect too. The Mag cylinder looks normal. This is a power valve engine. I have rebuilt Kawasaki's and Polaris' but never owned or worked on a Yamaha (I have two Kawasaki 1100STX and have had Polaris before). I ordered the Yamaha service manual ($75 ouch!), but I have not received it yet. My question is, can I replace the one piston without removing the engine from the waverunner? When I did my Kawasaki's, I had to remove the engine because the three piston cylinder casting is all in one. This ski has individual cylinders. By the way, I am also rebuilding the carbs. Should I do anything else like install the waveeater clips, or the SBT Lever links? Any help and other recommendations would be greatly appreciated. Thanks!