JH were the initials of James Howarth who produced motorcycles from 1914 to 1916 of the J. H. Motor Engineering Works in Castle Mill Street, Mumps, Oldham.
1914 In the October of 1914 James Howarth, who had once worked for Bradbury, offered his new range. At the bottom was a model fitted with a 269cc Villiers two-stroke engine and direct-belt transmission. There was also a machine fitted with a 2.75hp, 349cc four-stroke Villiers engine, two-speed gear and chain-cum-belt drive. Larger models were also listed using 6hp or 8hp JAP, or 6hp MAG engines, the MAG with a three-speed gearbox. A racing model was added in the November, fitted with a 3.5hp MAG engine.
1915 JH offered the two Villiers-powered machines, plus models using 3.5hp and 6hp MAG V-twin engines, the latter with a three-speed or four-speed gearbox.
1916 The engines used for that year were the 269cc Villiers, a 3.5hp JAP and V-twins of 3.5hp, 6hp or 8hp from MAG, or 6hp or 8hp from JAP.