Collectable: Vincent Grey Flash

In the Vincent world the humble 500cc Comet single is often treated as a poor relation to the 1000cc twin, but not the Grey Flash. Produced as a factory racer in the style of the Black Lightning towards the end of 1949 and into 1950, the Grey Flash is one of the rarest of all Vincents.

The Grey Flash grew out of the 500cc Comet, designed in 1935 by Australia’s own Phil Irving. Irving joined Vincent in 1930 after riding as passenger to Jack Gill in a Vincent-HRD sidecar from Melbourne to London via North America. When designing the Comet, Irving selected the bore of 84mm as the smallest cylinder he could get his hand in for cleaning. A 90mm stroke provided 499cc and these would be the dimensions of all Vincent singles and twins until 1955.

The most unusual feature of the Vincent engine was the valve train, which Vincent liked to refer to as “semi-overhead camshaft”. This wasn’t really correct, but the high camshaft allowed for shorter pushrods in splayed aluminium tunnels and reduced engine height.

Each valve moved through double guides, with the forked rocker acting on a collar in the middle of the valve stem. This reduced side thrust on the rockers and allowed for large hairpin valve springs to be externally mounted.

The layout was a superb engineering solution, combining the advantages of pushrod and overhead camshaft designs, and it became a Vincent trademark.

The success of the higher performance 1000cc Black Shadow and Black Lightning in 1948 led Vincent to release the Grey Flash towards the end of 1949. But unlike the Lightning, which was a pure racing model, the Grey Flash was available in three variants: racing, dual-purpose (with road equipment supplied) or with full road equipment.

Setting the Grey Flash apart from the Comet was a Lightning-spec engine, including big-valve head and 32mm Amal TT carb.

The engine bristled with special components, from higher-lift Mark II cams, polished conrods, triple valve springs, and opened-out polished ports.

With an 8:1 compression ratio and a 50mm straight-through racing exhaust, it produced 35hp (28kW) at 6200rpm.

At least three different types of gearbox appeared on Grey Flashes. Some had a pre-war Burman gearbox, at least one had an AJS 7R gearbox, but most had an Albion four-speed, available with either an aluminium or Elektron (magnesium alloy) case. Some Flashes were delivered with a kickstart and others without.

The Grey Flash chassis included the unique Girdraulic fork, but with specially milled fork legs, and a selection of Elektron components from the Lightning.

The rear suspension was similar to the road-going Comet, with Vincent’s own triangulated fork rear suspension set-up. In addition to the hydraulic damper some Flashes also had a sprung seat. The 20 and 21-inch wheels with light alloy rims and Elektron brakes were standard Lightning, but the grey colours were unique to the Grey Flash.

Although the 150kg weight was similar to the ‘featherbed’-framed OHC Manx Norton, except in the hands of John Surtees the Grey Flash couldn’t match the Norton on the track. And with full road equipment it was priced similarly to a 1000cc Rapide – about double that of a comparable Triumph or BSA parallel-twin.

At a time when Britain was still recovering from the aftermath of war no one wanted the single-cylinder Vincent, let alone the expensive Grey Flash. Beautifully executed and built to the highest standard, the Grey Flash was simply the wrong machine at the wrong time.

Many thanks to Allen and Lorraine Smith of the Australian Motorcycle Museum in Haigslea (Qld) for the use of the Grey Flash featured.

These are the numbers you’ll need to crunch to put a Comet Grey Flash in your own shed…

Story courtesy of Motorcycle Trader.