The 2¾ h.p. model was dropped from the range, and the 3½ h.p. model was
redesigned and produced in 'Standard' and TT versions. The
former model was also produced for the War Department as a 'General Service'
model (engines stamped 'GS').
Marstons issued both
pre-season and mid-season catalogues. The mid-season catalogue introduced a
re-engined v-twin model, an AKD (Abingdon
King Dick) engine of 798cc replacing the JAP engine from the previous year.
War production was making JAP engines hard to come by.
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Engine and Gearbox
The most notable visual change was the new parallel-sided magneto chain drive
cover for the single cylinder machines.
* Robert Cordon Champ, 1980, 'The Sunbeam Motorcycle'. Haynes Publishing.