THIS KIT HAS EXTRA PARTS YOU WON'T USE,, THIS WAY IT WILL WORK FOR DIFFERENT MODELS. FYI STOCK 50'S = 39MM ALL Z50A Z50R XR50 CRF50 = 39MM ALL XR70 CRF70 = 47MM CT70 ALL = 47MM ATC70 ALL = 47MM C70 PASSPORTS ALL = 47MM C70M'S ALL = 47MM 85CC KITS = 51MM 88CC KITS = 52MM TRX90 = 47MM TRX90 103CC = 51 TRX90 106CC = 52 THIS WILL WORK FOR ALL YEARS OF 50'S 70'S AND TRX90'S PICK_BORE_SIZE SEE DROP BOX BY ORDER BUTTON 39MM_ 200008 47MM_ 200009 51MM_ 200010 52MM_ 200011 TOP END GASKETS ** PICK BORE SIZE ** 39 47 51 52 MM 200008 / 200009 / 200010 / 200011$13.99PICK_BORE_SIZE: 39MM_20000847MM_20000951MM_20001052MM_200011