Custom Copy: 1937 Vincent TT Replica

Robert Watson's restored Vincent TT Replica had only 70 percent of its parts when it was bought.

| May/June 2016

1937 Vincent TT Replica
499cc air-cooled OHV single, 84mm x 90mm, 8:1 compression ratio (stock), 34hp @ 5,800rpm (stock)
Top speed:
115mph (est.)
Fuel capacity:
6gal (22.7ltr)
Price then/now:
£118 ($583)/$25,000-$65,000

When is a replica not a replica? When it’s the original, of course!

It’s perhaps unfortunate that Philip Vincent chose to call his customer race bike the TT Replica, because the name has been causing confusion ever since. At least one concours judge dismissed Robert Watson’s painstaking TT Replica restoration because he accurately described it as a “Replica” on the entry form. So just to get this straight: TT Replica was the name given to approximately 40 500cc Series A Vincent singles built by Vincent in Stevenage, England, in the late 1930s for sale to amateur racers. They were, just as the name implies, replicas of the factory race bikes that performed so well in the Isle of Man Senior Tourist Trophy race in 1935 and 1936.

The Series A singles

By 1931, engineer Phil Irving had joined Vincent-HRD after arriving overland from Australia as passenger on an early HRD sidecar setup driven by Yorkshireman John Gill. Irving’s first tasks were to design a semi-sprung passenger pad (something he no doubt had an opinion on after the trip from Australia!) and to create a new frame of more conventional appearance than the straight-tube item Vincent had designed. Conservative British buyers were suspicious of rear suspension, but Vincent would not compromise his engineering principles by building a frame with a rigid rear. So Irving placated the naysayers by hiding the spring boxes under the seat!

Vincent’s preferred engine was the 500cc Python overhead valve Rudge-Whitworth engine, although both sidevalve and overhead valve JAP engines were also used. As Rudge wound down its engine division in the early 1930s, JAP became the default option. However, when the JAP racing engines fitted to all three Vincent-HRD entries in the 1934 Isle of Man TT expired, Vincent decided it was time to make his own engine.

The result was an overhead valve engine incorporating many innovations. Broken valves were common at the time in overhead valve and overhead cam engines, especially in racing, perhaps a reflection of the relatively poor metallurgy. Vincent’s solution, though complex, was to reduce stress on the valve stem. A high camshaft driven by a bronze idler gear operated short pushrods. These in turn moved forked rocker arms, which actuated the valves by means of collars fitted in the middle of the valve stems. The valve itself was supported by two guides, top and bottom. This kept the valve train light, while minimizing side loads on the valves. Without rockers above the valves, there was room for race-style hairpin valve springs while still keeping the height of the engine at a minimum.

5/5/2016 8:08:40 AM

Really great write up that's easy to read, I was a "captive" till the end. Educated me on a truly unique machine, many thanks.

Ride 'Em, Don't Hide 'Em Getaway

Classic Motorcycle Touring and Events.

The latest classic motorcycle events and tours.