Custom Copy: 1937 Vincent TT Replica

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

1937 Vincent TT Replica

1937 Vincent TT Replica

Photo by Robert Smith

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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.

The first Vincent-HRD singles — the touring Meteor and sportier Comet — used a cast iron cylinder and head, and established the 84mm x 90mm bore and stroke used on all subsequent Vincent motorcycles. It was a compact engine with considerable tuning potential, a fact confirmed by the success of Vincent-HRD singles in the 1935 Senior TT, with Jack Williams and Noel Christmas finishing seventh and ninth, respectively. Jock West placed eighth in the 1936 race against the full factory-supported Norton and Velocette teams with their overhead cam racers. The Vincent-HRD became the little engine that could.

To celebrate its TT success, the factory released a limited run of TT Replica singles. Just like the race bikes, the TTR featured a composite cylinder barrel, with a finned light alloy “muff” cast in situ around an iron cylinder. Like the TT, the cylinder head was cast bronze (though at least one example is known to have received a light alloy head). A high-compression piston and factory “5X” competition cam were fitted, with fueling provided by a 1-5/32-inch Amal 10TT carburetor and sparks by a British Thompson-Houston (BT-H) “TT” magneto. The engine drove the multiplate clutch via a duplex primary chain, then to a Burman close-ratio gearbox.

The frame was essentially the same as used on the Python-powered singles, an open-loop diamond of lug-and-braze construction, with the engine plates and crankcase forming the bottom loop and Vincent’s own patented, triangulated rear suspension. Wheels were 19-inch rear and 20-inch front, with composite brakes — alloy drums with shrunk-in iron liners — and a Brampton girder fork. The gas tank and oil tank were fabricated in stainless steel, and light alloy blades replaced the Comet/Meteor’s valanced fenders.

While no rider was able to emulate Jock West’s 1936 eighth place in the TT, the TTR (and its post-WWII successor, the Grey Flash) proved very capable in clubman racing, where John Surtees got some of his first race wins. HRD-Vincent also produced a few road-going TTRs (the Comet Special) with a Miller mag-dyno and lights, and a slightly detuned engine — but still good for 90mph!

Robert Watson’s TTR

The story of the TTR featured here is inextricably entwined with the tale of the 1939 Series A Rapide twin featured in Motorcycle Classics in September/October 2012.

Robert Watson owns six Vincents, including three postwar Rapides and a Comet, plus two A models: the 1939 Rapide twin and the TT Replica single featured here. Watson acquired the TTR (or approximately 70 percent of it) at the same time as the Rapide. Both bikes came from a collector in Toronto, Canada. Watson was initially dismayed that a Vincent single was a mandatory part of the Rapide acquisition deal — especially at the considerable asking price — but that apprehension disappeared on learning that the single was a TTR!

Watson recalls his reaction: “I just about collapsed on the floor,” he says. “I just went: ‘TT Replica? It’s done. This is a done deal, right here, right now.’”

The Rapide got Watson’s attention first, but when that restoration was completed, he turned to assessing the TTR, which also came with a fascinating provenance. Watson has established that the TTR, engine number 121, was first sold in Vancouver, Canada, to a racer named Max Nerriere.

“His buddy was a guy named James Taylor,” Watson says, “who in the late 1930s was the Norton dealer in Vancouver. Nerriere read that Vincent was offering replicas of its TT bikes to the general public and got his buddy Taylor to order one.”

Nerriere raced the TTR at the Oakland Mile track in California, a fact established by a copy of a program Watson has from the 1938 AMA 200-mile race, listing Nerriere as a competitor on Vincent TTR #121. (The TTR numbering sequence runs from about 101 to approximately 140.) “It didn’t finish,” Watson says. “It blew the big end up the first year, and the second year (1939) the magneto died in practice.”

Nerriere moved east to Ontario, Canada, and sold the TTR to two racing brothers, Byron and Robert Sparks. They used the TTR for grass track racing together with another TTR they owned, number 110. Through various contacts, Watson has established that the TTRs were seriously mistreated on the grass tracks before being retired. “They were absolutely beat to crap,” he says. “The tank that’s on mine now, if you’d seen it when I first got it … it must have had 50 dents in it.”

The Sparks brothers did do Watson a big favor, though. “The Sparks brothers, after the war, ordered from the factory a new frame for the TTRs, because they had smashed them up.”

The new frame was included with the pile of parts Watson acquired. He checked both the original frame and the new one on a truing jig: The old frame was badly out of shape, while the new one was perfect. So TTR121 ended up with a new main frame.

The restoration

When Watson finished inventorying the parts he’d bought, he realized what he was up against. “It was maybe 70 percent there,” he says. “It was all in pieces. The crank and the cases were there. The cylinder was there, but it had been blown up at one time.”

A large chunk was missing from the iron cylinder below the alloy “muff.” A repair had been effected by brazing the piece back in, then boring and sleeving the cylinder.

“On an A there’s nothing to hold the liner,” Watson says. “They’re Al-Fin cylinders, where the aluminum is cast right around the iron. When they pressed the sleeve in, they drilled holes through the original liner and the new liner and filled (the holes) full of brass as anchor pins!” Ingenious though the repair was, Watson decided on a complete new cylinder from Maughan & Sons Engineering in the U.K.

“The bronze cylinder head had been sent out to have new valve seats put in it,” Watson says, “and because they were bronze heads, they made new bronze seats and welded them in. So it had new bronze seats in it, which we basically got to put the first cuts into.”

The “we” refers to Watson’s good friend and expert machinist Dan Smith. “We made all new valves for it. We cut down valves meant for a Chevrolet 454 V8 engine, and because the valves have a step in them, we had to turn them down and finish-grind them. We put in post-war-style Vincent collets — the pre-war types are sort of screwed together and they’re a real pain to deal with,” Watson says. “The bronze heads had no provision for a compression release, which makes it interesting to start, because it has an 11.5:1 piston in it!”

The primary drive, cases and clutch were completely missing. Fortunately, Smith had a pattern for the inner primary from one of his own projects (another Series A twin), the inner primaries being common to the Series A twins and singles. Smith also produced a pattern for the outer primary from scratch.

“The twin outer primary is different because the twins had a much bigger clutch,” Watson says. The clutch is a modified Honda item, but it required considerable extra work by Watson making adapters and sprockets.

“The original TT bikes had Albion gearboxes, and the Replicas had close-ratio Burman gearboxes,” Watson says. The box now in the TTR was assembled from parts of various Burman gearboxes, with some new gears and shafts, courtesy, again, of Dan Smith. It has standard ratios.

The magneto came from Dave Lindsley in England. “They originally had a BT-H magneto in them with a mechanical advance. Typically of Vincent, they run the opposite way from everyone else’s magnetos,” Watson says. The magneto now in place is embossed AEI, not BT-H. Associated Electrical Industries was the parent company of BT-H, and for a while they used the AEI brand instead. “It’ll throw a spark about 2 inches,” Watson says, “and it starts and runs the bike really well.”

The rear frame had the whole top end of it cut off so it was essentially just the swingarm without the top triangle piece. But also in the parts Watson acquired was another complete but unnumbered rear frame. Watson considered using the new undamaged rear frame, but that would have compromised the TTR’s originality. Instead, Watson and Smith used the new frame to construct a jig so Smith could repair the original frame. “I ended up with a matching rear frame to the engine,” Watson says.

Also included in the parts stash was the original carburetor, a 1-5/32-inch Amal 10TT in zinc alloy that was in “pretty ugly shape.” Watson had a 10TT in brass that he wanted to use instead, “but the float angle was wrong,” he says. “We tried to tweak the float angle and broke it.”

Using other 10TT parts he had, Watson made up a remote float chamber with a separate adjustable mounting. “So it’s now a 10TT9 with a brass remote float, and I can adjust it up and down to where it needs to be,” he says.

The next project was the oil tank. The original unit, soldered up from steel sheet, was badly pitted. The solution was to build up the surface by repeatedly copper plating and polishing it, so the copper filled in the pits. The tank was then nickel and chrome plated. “It actually turned out pretty nice,” Watson says.

Mounting the oil tank presented another obstacle. “I could not work out how it mounted until I started looking at pictures. It has upper rubber mounts and lower rubber mounts. There are four bolts at the top and four bolts in the bottom. It took me quite awhile to sort that out and make it all fit,” Watson says. Though he found a pair of wheel hubs with the parts stash, there were no brakes or rims. “The TTR had composite brakes, with a circular cast iron ring, which was the drum, bolted to the alloy side plate.” The TTR now has reproduction TTR brakes on the front (originating from an aftermarket supplier in the U.S. during the 1960s) on the original TTR hubs. The front rim came from an AJS 7R, and the rear is an older Akront or San Remo, he thinks.

Watson had the gas tank dismantled and beaten out, then Vincent guru John McDougall (now deceased) soldered it back together again. “It’s not perfect, but they were hand-built tanks in the first place, soldered up from pieces of stainless steel, and it was a race bike, you know.”

Watson thinks the seat is not correct, but “when you were racing, you didn’t sit on that; you sat on the bum pad on the back fender and crouched your neck down,” he says. “It had no rear seat at all, none of the stays, which were exclusive to the TTR. They were totally different than the road bikes.”

Watson was able to make new stays from sketches taken from a TT. Most TTRs have a bobbed front fender and no front stay, but Watson opted for a full length fender with the stay to support it. He made the 1-inch handlebars himself. A period correct tachometer was sourced, but it had the wrong gears. A replacement set came from KTT Services in Australia.

The finished restoration is a fitting tribute to Watson’s and Smith’s persistence and determination — not to mention engineering, machining and fabrication skills, and it offers a unique insight into the minds of two of the world’s most respected and influential motorcycle pioneers: Philip C. Vincent and Philip E. Irving. MC