The Model 18 was a significant step for Norton – and one which came at a challenging time.
The vintage era years had seen them forge a formidable reputation for sporting performance with their side-valve singles – thanks in no small part to rider/tuner Dan ‘Wizard’ O’Donovan, who himself would notch up 112 records on the Brooklands concrete on a record-breaking motorcycle that would come to be known as ‘Old Miracle’.
Doubtless it was a reputation the factory wouldn’t want to do anything to jeopardise in a hurry and so it was, I’d imagine, with some trepidation when they decided it was time to keep step with rival manufacturers and switch to the newfangled overhead valve (OHV) figuration. So important was the engine in fact, that its design and development was personally overseen by the firm’s founder James Lansdowne ‘Pa’ Norton.
The new overhead valve top end was fitted to the well proven bottom end already in service in the 16H; its cylinder retained the 79mm x 100mm bore and stroke. The rockers were placed high above the head on pillars ensuring adequate cooling, with both head and cylinder benefiting from large well-spaced finning for the same reason.
