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This paper reviews the progress made since the last SAE Congress in the development and testing of the Collins Scotch Yoke crankshaft technology and the demonstrator engine in which it is being proven. New packaging refinements are illustrated, and more detailed internal friction loss data are shown. New fuel consumption data are shown to confirm the low internal friction losses of the demonstrator engine. A study of the potential of supercharging illustrates the power increase that can be achieved with virtually no increase in engine packaging volume. A discussion is also provided of the unique, exact engine balancing that is possible with the scotch yoke technology, due to the pure sinusoidal motion of the pistons and con rods. Finally, a brief discussion is provided of the small crevice volumes that may be achieved with the Collins Scotch yoke technology.

Recent studies have confirmed that it is possible to achieve perfect balance of all forces and moments created by pistons, connecting rods and crankshaft of the Collins family of 12, 8, 6 and 4 cylinder engines. With the Scotch Yoke mechanism there are no secondary forces, or higher order forces, and thus the counter-balancing needed can be determined exactly. The pure sinusoidal, translational motion of the pistons and connecting rods and the pure rotational motion of the crankshaft and bearing blocks makes the calculation for balance “trivial”. In all cases, except the 12 cylinder model, a single balance shaft rotating counter to the crankshaft rotaion, at engine speed provides complete cancellation of the moments created by the moving parts of the engine. Alternatively, two small balance shafts can be used, located in less space sensitive spots than the single balance shaft. In the case of the twelve cylinder engine, no balance shafts are required.