The easiest way to get 106cc power from your CRF50 and CRF70 - Takegawa 106cc SCUT bore kit is a quick top end bolt on kit with 57mm skirtless piston and cylinder. no case boring required. Kit also comes with the Takegawa Supersport camshaft for stock head to make the most out of this displacement. Works really well with PC18 and PC20 carburetors.