Oil boiler

 Granville Bradshaw, who had many innovative engine-related designs in the first half of the last century, designed this oil cooled 500cc flat twin in the early 1920s. The cylinders were located inside the crankcase and were cooled by oil splash. The engine was derisively referred to as the "oil boiler" but it apparently worked well enough. He apparently believed the hotter an engine ran, the more efficient it was. Incidentally, this drawing is billed as the first fully sectioned motorcycle engine cutaway to appear in print, the artist's name is not noted and the signature is not clear enough to decipher.

Suzuki resurrected the oil cooled idea with its first generation GSXR SACS engines, where engine oil was circulated by a high volume pump and kept cooled by an oversized oil cooler (radiator). Increasing heat from higher output led them to adopt liquid cooling in the early nineties.