The Harley-Davidson Twin Cam engines are motorcycle engines made by Harley-Davidson since 1998. Although these engines differed significantly from the Evolution engine, which in turn was derived from the series of single camshaft, overhead valve motors that were first released in 1936, they share a number of characteristics with nearly all previous Harley-Davidson engines. Both engines have two cylinders in a V-twin configuration at 45°, are air-cooled, and activate valves with push-rods. The crankshafts have a single pin with a knife and fork arrangement for the connecting rods. These are sandwiched between a pair of flywheels.