Wednesday 18 July 2012

Factory Tuning Instructions

(click this link for a PDF)

-SG- Peter Thomson in New Zealand has kindly provided these copies of Tuning Instructions issued by the Norton works in the mid-twenties (late 1924 - early 1925). These are worthy of attention by anyone who wonders about the performance private owners managed to extract from their Model 18s at the time. Note the suggested substitution of an exhaust cam for the regular inlet version - this would probably have been in the era of the '90' cams - and also how to increase the compression ratio by machining the cylinder base. The notes came to Peter through descendants of a leading rider in the Otago region of New Zealand (south of the South Island) called Josh Mewhinney. Josh was successful in beach racing and hill climbs in the twenties and thirties.