Having hitherto relied on proprietary engines, Norton introduced its own power unit in 1907. The long-stroke sidevalve single displaced 633cc and the new model it powered became known as the 'Big 4'. Smaller capacity versions followed and in 1911 the 500 adopted the classic 79x100mm bore and stroke dimensions which would characterise the half-litre (actually 490cc) Norton for the next 50 years. The 490cc engine was revised for 1914 and in 1921 the Model 16, as it had become known, received a new lower frame, becoming the 16H. Norton's trusty sidevalve would be continuously up-dated for the next 30-plus years, many seeing service with Allied forces in WW2, before taking its final bow, together with the Big 4, in 1954.

The vendor's father recalls that he spent many happy hours riding this modified 16H around the Devon fields. Accompanying paperwork consists of old/current Swansea V5/V5C documents and a green continuation logbook (issued 1975) listing the vendor's father as '1st Change'. It should be noted that the engine is a later replacement unit and not the original ('A23936') which is still recorded in the aforementioned documentation.