this 2004 Polaris Sportsman 600 if fine at idle but when you give it throttle it starts to knock, the owner seems to think its a cracked piston skirt?
Opinions?

 

It could be a broken piston skirt, but doesnt sound like it to me.

Pull the topend off (pistons & all) & check the crank (big end) for rod movement. If that isnt it, most likely your main crankshaft bearings. Which would require splitting the cases to get to & replace..... Not an easy task

Some people have been known to use a stethoscope to locate the position of a knock either in the cylinders or in the lower end.

 

how likely is it something to do with the crank shaft as i dont want to replace another one of them buggers. This isn't my quad but i might be buying it.

 

likely, its either the crank or the bearings if the noise is coming from the lower end.