Classic Spagthorpe:
Wrestler

There was, of course, the Spagthorpe Wrestler engine, which was a horizontally opposed twin having no crankshaft and a single rod connecting the two pistons. Teeth on the top and bottom of this rod drove gears which transmitted the motions to the gearbox. The pistons were lead weighted to provide sufficient momentum to complete the complex Three-And-A-Half-With-A-Wiggly-Bit-Thrown-In-For-Good-Measure stroke system that was the masterstroke behind this engine.

The only drawback to this design was that occasionally the engine revs would match the sympathetic resonance of the machine (strict luggage loading instructions had to be adhered to for warranty purposes) and the bike would disintegrate spectacularly in an explosion of motorbike and human parts. If you were strong and agile enough, you could disperse the standing waves and prevent this unfortunate incident. Hence the name Wrestler.