 A number of modifications were made to the locomotive including a new design of boiler, for the production version.The 500th QJ was built in 1968, the 1000th in 1970, the 2000th in 1974 and the 3000th in 1979, with production rates varying from 150 to over 300 per year between 1966 and 1985.Production ended in 1988.