Responded 5 days ago... Turning 30 inch wheels and tires on a machine designed for 25 or 26 inch tires with 28 gram weights is OK. Turning 26 or 27 inch tires on a Grizzly or Kodiak which has been weighted to 18 grams of weight would be ok as well. BUT, if the original owner slapped on 30 tires without changing the ratio in the CVT such as shimming, weights or springs....it's no wonder the pinion gear teeth was sheared off by the drive shaft, or always rode in diff lock on pavement. There is a significant increase in tire weight for every inch in tire diameter. Thats unsprung tire weight that the engine has to turn. Too much rotational resistance and the weak point was the pinion gear. It's like starting off in 4 gear in a car, you're labouring the engine and associated drive train. Sorry about your troubles but you should verify what exactly was done to the CVT. As well, there is lots of information on ATV tire sizing regarding the positive and negatives to increasing tire sizes and the steps you can take to ensure you don't damage the machine. Now head gaskets blown...sheesh. Without mincing words I'de say the guy who sold you the machine was dumber than a bucket of hammers in regards to modifying the ATV. Who knows what else he did to it.