 The concept was then further developed – as Monty had done with the BSA Gold Star engine – by reducing the 650 cc capacity to under 500 cc, retaining the standard bore of 71 mm but shortening the stroke to 62.5 mm, using a new crankshaft having a shortened throw made by sidecar racer Owen Greenwood together with 10 mm shaved-off the standard cast-iron barrels.Additionally, an option was to instead fit the contemporary Triumph production engine with a standard 500 cc capacity.Both types of engine were tuned and built by Allen Dudley-Ward featuring his Manx Norton oil pump conversion.