THIS WILL WORK WITH THE FOLLOWING HEADS THEN C70 PASSPORT 1980 AND 1981 Z50 HEADS ALL THRU 1981 STOCK XR70 CRF70 AND TRX90 HEADS E22 HEADS WITH 20 AND 23MM VALVES MOST ANY CHINA HEAD WITH 20MM AND 23MM VALVES 88cc_CYLINDER_KIT C70_1970_to_1981 Z50'S_69_TO_81 88CYL/1-33/2-11$119.95 52MM_PISTON_KIT (OLD_50_DOME) OR (NEW_70_DOME) (SHORT_ROD) (100033)THIS PISTON WILL WORK WITH THE OLD STYLE PRE 81 SHORT CONNECTING RODS AND THE STOCK Z50 HEADS THAT ARE ALSO 1981 AND OLDER. WILL WORK WITH NEW_70_DOME HEADS TOO * THIS IS A 52MM BORE PISTONAND NEEDS A SPECIAL CYLINDER AS THE STOCK 50 AND 70 CYLINDERS WON'T BORE OUT THIS BIG. 100033$48.95