The S&S KN-Series engines are very close in appearance to a stock Knucklehead engine, but offer a number of modern features for more power, better engine life, and improved reliability. Available as 74CI (more exact 73.7CI or 1,208 cc) or the much larger 93CI (more exact 92.9CI or 1,523 cc) displacement, the main improvement in design is the 1958-1965 style flywheel assembly, which uses a splined sprocket shaft and Timken sprocket shaft bearing. Although this necessitates the use of a 1954-1965 style inner primary cover and primary chain sprocket, the increased flywheel stability, strength and power handling capacity are worth a slight departure from stock. Flathead Power rocker arm cover "tins" are another modern improvement. The lower covers are actually made of die-cast aluminum and instead of being held in place by the valve guide, it is now being held by the valve spring pressure. A special gasket on the bottom of the lower "tin" provides a positive seal and is much easier to service if needed, since the valve guides do not have to be pressed out in order to remove the lower covers. Also instead of the steel brazed-in hard oil return lines used on stock tins, S&S has improved the design of the oil line for better reliability and easier assembly and maintenance. The KN series engines come assembled and complete with an S&S Super E carburetor and S&S Super Stock ignition and feature a one-year warranty. KN74 engine fits 1936-1999 style chassis. KN93 Generator style engines fit in stock and stock style Knucklehead frames with a 1954-1965 style inner primary housing and primary chain sprocket. Alternator/Generator style engines do not fit in stock Knucklehead frames as these engines have a 1948-1999 style front motor mount and must be used with a 1970 or later style inner primary.