Dirt Bike FAQ

To be competitive in this class, and since no manufacturer is currently offering a 105cc model, this is the only option.

Standard cylinder on this enigne in nikasil. No sleeve.

To do a big bore kit you will either need to have a liner installed in the cylinder (not the most reliable option usually), or purchase a complete kit which includes a bored and re-nikasiled (or other plating) cylinder.

Because of the change in cylinder volume, standard porting will NOT work. The porting needs to be matched to the new engine displacement.

You can purchase a complete setup like this from shops like Lukes http://www.lukesracing.com/luksr/cr85bigbore105p04.htm

Another option which will actually give much better overall power is an increase and bore and stroke to the new 105cc AMA limit. It's more expensive, but will give at least 20% more torque and midrange power than just a bigger piston.

Companies like Max Power offer these kits http://www.maxpower-engines.com/big-bore-kits/cr105.htm

He'll have to also remember that putting this much more power thru the engine can result in decreased lifespan of transmission and clutch components. Just something to keep in mind!