The 2008-2014 Nytro or 2014-15 viper cranks all need to be drilled and tapped to accept the bolt to hold the crank stub on. it is a M10x1.25 tap. The 2016+ Viper or 2017+ Sidewinder engines are ready to accept the the bolt as they are tapped from the factory.
If you are installing a Nytro or Viper engine into a YXZ, you will need to purchase the stiffer valve springs. If you are installing in the Wildcat XX, the Nytro or Viper valve springs will be sufficient. If you don't want to fab your header to the snowmobile head the Exhaust adapters will work for you providing the current header has rotating flanges.
