engine was runing like it was working real hard try to stal thought it was a plug changed them abought a mile later it died whould not restart after i got it home try to start it it puled real hard copresion seams cilinders look all right put a small flash light in the exhahst y pipe look threw plug hole looked good it tries to start makes a clunking sound think it a crank bearing ?what do you guys think would cheaper to rebuild or new engine wear a good place to buy a artic cat 550

Replacement will be cheaper, but you will have another old engine. A complete rebuild / overhaul will give you something as good, or almost as good as new. find out what is wrong with it first, that will help you figure out which direction to go.