1936 Norton Model 18 vs. 1938 Velocette MSS

Two of the best representatives of girder-forked 500cc British singles

| May/June 2011

The 1930s were the golden age of the British motorcycle industry. And just as the four-cylinder DOHC became the signature for the UJM — Universal Japanese Motorcycle — of the 1980s, the 500cc OHV four-stroke single with girder forks was the default UBB — Universal Brit Bike — of the era.

Just about every major British manufacturer made a 500cc single — BSA, Triumph, Norton, Velocette, Sunbeam, Rudge, New Hudson, Excelsior, HRD, New Imperial, Royal Enfield, they all had one. But two of the best were the 1936 Norton Model 18 and the 1938 Velocette MSS.

Norton built its first overhead valve single in 1923, the 500cc Model 18. An instant success both on the street and the track, a Model 18 took Alec Bennett to the winner’s podium at the Isle of Man TT in 1924.

In 1927, Bennett again won the TT, but this time on a new Norton, the CS1 with its Walter Moore-designed overhead camshaft engine. In 1928, the “cammy” CS1 appeared in Norton’s catalog, together with a new street bike using an overhead valve engine that borrowed heavily from the CS1, the ES2. All three machines shared the same 79mm bore by 100mm stroke, numbers used on every road-going 500cc Norton single for 40 years until the last ES2 of 1963. Though almost identical to the Model 18 on paper, the ES2 included many detail improvements over the 18 and was sold alongside it until the Model 18 was dropped in 1947. Even so, it was the 18 that earned Norton its sporting reputation in the 1930s.

Velocette had been building road machines based on its race-winning 350cc KTT overhead cam bike from the late 1920s onward. But the “cammy” engines were expensive to produce and left a big hole in Velocette’s model range, with the sporty overhead cam bikes on one end and the company’s prosaic two-stroke 250cc GTP on the other.

In June 1933, Velocette announced an innovative 250cc overhead valve single to bridge the gap. In order to minimize the reciprocating mass in the valve train, the camshaft was positioned as high as possible, keeping the pushrods short. The model MOV had a top speed of 60mph right out of the box, very impressive for a 250cc machine of the era, and tuned versions eventually reached 100mph. So successful was the MOV that Velocette introduced a longer stroke 350cc version, which became the MAC. The big bore 500cc MSS followed in 1935. Intended primarily as a sidecar tug, the MSS proved to be equally proficient as a solo machine, and enjoyed a production run (as MSS and later as the Venom) that lasted 35 years, until Velocette closed in 1971.

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