Big Bore cylinder and piston kit- The only complete bolt on big bore 750cc Big Bore Cylinder and Piston Kit The Only complete bolt-on Big Bore 750cc Cylinder and piston kit ever made for the XS650 Yamaha Modified limited production European Race Engine Cylinder Block has enlarged fins for improved cooling. The New Cylinder Block has longer fins matching the Head Fin Length. Kit Fits: 1974-84 447 Type Engines Kit Includes: 1. XS Performance Big Bore Race Cylinder Block with sleeves installed and finished to fit our 80mm. Forged Big Bore (750cc.) Pistons. Cylinder casting has larger cooling fins that extend out the same distance as the cylinder head fins for enhanced cooling. No modifications to engine cases needed. 2. Forged 80mm. 750cc Big Bore Piston kits(2) complete with Ring Sets, Piston Pins & Clips. Forged 447 type Pistons feature: 1. Valve pockets cut for large valves. 2. Mos2 treated piston skirts. 3. Oil channel for enhanced piston pin oiling. 4. 20mm. piston pins that are internally tapered to ends for weight reduction. 5. Lightweight 9:1 compression pistons. Assembly - Weight approx. 455 Grams. 6. Big Bore Cylinder Head Gasket & Base Gasket. Fitted with our XS Performance Camshaft, Dellorto Carbs, a free-flowing Exhaust and Iridium spark plugs will result in about 65 Rear wheel Horsepower or more and 50 foot-pounds of Torque. See Dyno Chart 1 Dyno. Note: Stock Cylinder bore size is usually about 75mm. Stock Piston size is around 74.945mm. and the Standard size piston has.945 marked on its top (the "74" is always  dropped). Standard original piston size varies slightly so the piston may also be marked .965 or otherwise. Standard bore clearance is 0.0020- 0.0022 in. ( 0.050- 0.055mm). Oversize pistons are marked in mm. A 1st.over piston is marked 0.25 which is equivalent to 10 thousandths of an inch . 2nd. OS is marked 0.50 etc. Top and 2nd. Ring End Gap (measured in cylinder) should be a minimum of 0.008" and Oil rings should have a minimum gap of 0.012". Part #05-0750