Note: This camshaft has been designed to work with the OEM Yamaha piston, or the BBR big bore kit piston, with OEM sized valves. Any other combination of parts will require that you manually check valve to piston clearance. This is typically done by assembling the motor with clay on the piston dome and carefully rolling the motor over by hand. The motor is then disassembled and the thickness of the clay is measured. We generally shoot for .050" of clearance on these smaller 2-valve air-cooled motors. If you don't understand this process you should check with a qualified performance engine buider. We can only support our own BBR products.