New 350 And More

Despite the country and world starting the slide into recession, in the mid-1920s JAP remained outwardly buoyant, as publicity material depicted then modern manufacturing, plating and assembly shops, and even a repairs section for customer motorcycles.

As 1923 dawned, over 20 British makers – including Brough Superior, Coventry Eagle and Morgan – fitted JAP engines to some/all of the machines they made. JAPs were also employed by makers of four-wheel cyclecars, and overseas makers. Add to this that Bert Le Vack, Vivian Prestwich, Teddy Prestwich, Stan Greening and others were earning JAP engines many plaudits at Brooklands, and more were doing well for the company in other fields, it should have boded well – and to an extent it did. But JAP was challenged weekly by Blackburne, plus many small makers who employed proprietary engines were stopping production while more big, volume players used their own.

In April 1923, JAP unveiled a new engine, the 346cc (74 x 80mm) ohv single, aimed at racing and fast roadsters. Features included a detachable semi-hemispherical cylinder head, large for a 350 tungsten steel tulip valves, alloy domed piston, roller big-end, hollow pushrods, hollow tappets and generous cooling fins.