THIS STROKER KIT WILL LET YOU KEEP WHICH EVER 47MM OR BIGGER PISTON, CYLINDER AND HEAD YOUR USING NOW,, ON THE LISTED MODELS. THIS KIT DON'T NEED THE PISTON SKIRT TO BE TRIMMED !!! THIS IS HUGE AS FAR AS LONG TERM DEPENDABILITY GOES. THIS KIT USES BIGGER CYLINDER STUDS FOR THE ADDED POWER, 7MM HEAD NUTS AND WASHERS ARE INCLUDED. BECAUSE OF THE LARGER STUDS YOU MAY HAVE TO DRILL OUT THE HOLES IN THE TOP HEAD COVER TO 5/16" OR 8MM. IT IS VERY EASY BECAUSE IT IS ONLY SOFT ALUMINUM AND 3/8" THICK. THE HEAD AND CYLINDER HAVE BIG ENOUGH HOLES FOR THE BIGGER STUDS ALREADY. WE HAVE INCLUDED 2 6MM NUTS SO YOU CAN USE THEM LOCKED AGAINST EACH OTHER TO REMOVE YOUR OLD 6MM STUDS. THIS KIT WILL ADD A BUNCH MORE POWER, JUST BE SURE TO MATCH IT UP WITH THE CORRECT CARB AND FILTER TO GET THE MOST OUT OF IT. BECAUSE OF THE STROKE ON THIS CRANK YOU MUST CHECK THAT THE CRANK WILL CLEAR THE OIL PUMP DRIVE SHAFT. IT DID ON OUR TEST ENGINE, BUT IT WAS CLOSE. IF YOU NEED TO YOU CAN REMOVE A BIT OF METAL FROM THE SHAFT. YOU MUST USE A PISTON THAT WOULD/DID WORK WITH YOUR ENGINE BEFORE YOU ADDED THIS CRANK KIT. ONE LAST NOTE, BECAUSE OF THE SPACER PLATE, YOU SHOULD RETORQUE IT AFTER YOU RUN IT FOR AN HOUR OR SO. FYI THIS KIT IS FOR THE 63MM TALL CYLINDER THIS KIT HAS THE SAME DECK HEIGHT AS CRF50/70'S HAVE THIS IS A TRUE LONG ROD STROKER CRANK SO EXPECT WAY MORE TORQUE AND A LONG DEPENDABLE LIFE (: 51mm_STROKER_KIT FOR_47MM+BORES XR50_CRF50 XR70_CRF70 Z50R_1988_&_UP 91_TO_94_CT70 (51/STROKER/KIT) 51/STROKER/KIT * * YOU CAN USE THIS KIT WITH 1982 & 1983 Z50R'S, 82 AND 83 PASSPORTS AND 1982 CT70,, IF YOU USE THE 2 PARTS BELOW WITH THE STOCK OIL PUMP *SPINDLE OIL PUMP DRIVE (81L)THIS IS AN OEM OIL DRIVE SPINDLE. FITS: CRF50 2000 TO 2009 XR50 ALL CRF70 2003 TO 2009 XR70 1997 TO 2002 Z50R 1984 TO 1999 81L$15.70 *BUSHING OIL PUMP SHAFT CRF50 CRF70 TRX90 (251A)PIVOT, OIL PUMP FITS: CRF50 2000 TO 2009 XR50 ALL CRF70 2003 TO 2009 XR70 1997 TO 2002 Z50R 1984 TO 1999 251A$3.71