Rex-JAP were motorcycles produced from 1912 to 1916, by the Rex Motor Manufacturing Co of Coventry, and sold by the Premier Motor Co of Birmingham.
They produced a range of singles and V-twins using JAP engines in their existing frames. To begin with the machines had two-speeds and belt drive, but by 1914 there were only V-twin engines, but with three speeds and all-chain drive.
Thus they continued until 1916, but were not revived after the war.
See Also
Sources of Information
The British Motorcycle Directory - Over 1,100 Marques from 1888 - by Roy Bacon and Ken Hallworth. Pub: The Crowood Press 2004 ISBN 1 86126 674 X