J.A.P. (the brand name for John Alfred Prestwich's engine factory) was an English engine manufacturer that was very well known between the two World Wars, especially for the air-cooled V-twin engines they made for high performance motorcycles and the three-wheel Morgan car. After WW2 they were absorbed into Villiers. They made single cylinder engines as well as the V-twins, including some boring ones for Rotovators. You might want to start your research here:
http://en.wikipedia.org/wiki/JA_Prestwich_IndustriesSome of their products were somewhat respected in high performance circles, but a lot of them were just air cooled stationary engines.
