Motosantigua states that the displacement is 965 ccm, however a late 1922 article in The Motor Cycle gives 85.5x85 mm. (976 c.c)

Royal Enfield Motorcycles 1923

Motos Antigua HD, Spain

Motos Antigua HD offers high quality vintage motorcycles from Europe, the UK and the United States, with a focus on US Army and Wehrmacht military machines.

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