Sputhe R Flat top piston 95CI +.020
Sputhe engineering has been manufacturing aluminum cylinders with cast in liners for Harley-Davidson since 1977, far longer than Harley-Davidson themselves. Their Nitralloy big bore cylinder assemblies for Big Twin, Evolution engines are thoroughly tested and manufactured from the best materials available to the most exacting standards in the industry. Nitralloy cylinders are cast in 383 aluminum, which has a tensile strength of 45.000 p.s.i.The aluminum is injected into a steel die at over 5.000 p.s.i., assuring perfect bond to the Lascomite sleeve. Lascomite is a "class 40" high tensile chrome-moly alloy having a high molecular pearlite structure. It is centrifugally spun cast and heat treated to a hardness of 200 Brinell. Not only is Lascomite harder than the cast iron that Harley-Davidson and the other aftermarket cylinder manufacturers use, it is much tougher and less brittle.The Lascomite sleeve in the Nitralloy cylinder is 60% thicker than the sleeve in the stock Evolution cylinder for increased rigidity. Nitralloy cylinders are stock height so that the cylinder studs, pushrods, exhaust pipes, manifold and motor mounts do not need to be modified. Heads and cylinders can be removed with the engine in the frame. The pistons are machined from zero silicon, high nickel T7
stabilized aluminium forgings. The cam and barrel taper skirt configu-rations were developed by computer thermal Expansion Modeling. Long full width skirts provide maximum stability for a superior ring seal. Both dished and flat crown pistons are available. Nitralloy piston pins are machined from solid billet E52100 bearing steel with a tensile strength of 300.000 psi. The Big Twin 104 cubic inch kit uses 4 5/8" stroke flywheels. We recommend ZPN 232719 flywheel set, which is manufactured by S&S and has a 1/4" smaller diameter flywheels for maximum piston skirt clearance.
Note: When kits are installed following (in kit enclosed) installation instructions, the dish top piston will give a compression ratio of approximately 8.5:1. Flat top piston will give approximately 9.8:1.
Complete Big Bore kits are no longer available, but we still have replacement piston kits