The Long Harlequin is a two-cylinder horizontally opposed aircraft engine.
The Harlequin engine was developed as a replacement to the Heath-Henderson B-4 engine used on the Long Henderson Longster homebuilt aircraft.
The cylinders were based on a 74 cubic inch Harley Davidson JD Engine with connecting rods from Continental built Star auto engine.
The builder was expected to machine their own crankshaft, Les Long cast and sold crankcases[1][2][3] Dart Airport Museum in Mayville NY Oregon Aviation Historical Society Cottage Grove Oregon Glen Curtis Museum Hammondsport, New York Two other examples known in private collections