The P-61 American Rocket is one of the most unusual motorcycles you'll find, made from mostly stock parts. But the parts don't just come from one manufacturer or even just motorcycle manufacturers, they come from companies that produce both cars and motorcycles including pieces from Ariel, Indian, Ford, General Motors, Chrysler and Autolite.
The P-61 is the creation of Sam Pierce who had a long history with Indian motorcycles, starting with a cross country ride in the 1920's on an Indian Scout to becoming the curator of the Steven McQueen motorcycle collection in the late 70's. Sometime in the 1940's he started to design and build the P-61, but it wasn't until 1952 that he succeeded in building two working prototypes. One was built for show and the other used for testing.
The motorcycle was powered by an Indian Chief motor, whose cylinders had been cut down to 61 ci and fitted with sleeves and pistons from a Mercury automotive engine. The pistons were connected to the crankshaft using Ford connecting rods and the crankshaft rode on one set of plain bearings and a second set of ball bearings to provide a fail safe if one set wore out. The engine was rubber mounted to a skid plate using six neoprene collets from Chrysler spring shackles and was the first motorcycle to use vibration isolation as part of the engine mounting system. The top motor mount came from Chevrolet automobile. Since the engine was mounted to the skid plate, it could easily be removed from the frame by just removing the skid plate's mounting bolts. The frame came from an Indian 841, which was an experimental Indian built for the US Army in 1942. The 841 frame was chosen because it was 21 pounds lighter than a standard Chief frame. For the front end, Pierce chose a set of forks from an Ariel Square Four motorcycle, topped with a sealed beam headlight mounted in a nacelle along with an Oldsmobile horn.
Pierce had hopped to convince Indian to build a motorcycle like the Rocket, but Indian would close it's doors in 1953 without producing a single P-61. Pierce went on to form a company called American Indian and produced a limited number of Super Scouts and 640 Scouts using NOS Indian parts.