i thinking of getting a pro x 800 is there any thing i could do to keep the crank from failing

Not every 800 will have the crank fail, just so you know. If you want to do everything you can to prevent it you should talk to Dan at Indy Specialty in Shakopee, MN. His email address is indydan1@hotmail.com. There is ALOT of info on SnoWest and here about the 800 crank failures.

I would check the run-out on the crank before you buy it. Then if you buy it, get a one piece motor plate for it, torque arm, push arm, make sure all motor mounts are good, get the clutch balanced and shimmed correctly., rebuilt too if it needs it. After that, you must religiously check the torque of the clutch, that motor mounts are in good shape, torque/push arms set correctly. These things will definitly help the motor live longer, assuming the motor is in good shape to begin with.