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
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