During the 1960s a wide variety of machines catered for the novice racer, at least in the 250 class where Cotton, DMW and Greeves among others all offered competitive mounts. Anyone wishing to start his or her career in the 500 class however was faced with the prospect of purchasing and maintaining a much more expensive Manx Norton or Matchless G50. It was precisely this state of affairs that prompted two brothers from South Norwood, London - Peter and Philip Green - to manufacture an inexpensive, over-the-counter, clubman's racer. Ex-S E Centre grasstrack racers and proprietors of the engineering firm W A Green & Sons, the duo formed a subsidiary company - Dynamic Balancing Engineers Ltd - to manufacture the 'GB500'.
The GB500 used an overhead-valve Matchless G85CS moto-cross unit tuned by ex-AMC race mechanic Jack Emmott, whose main activity was the building of G85-based engines for speedway and grasstrack. Indeed, the Emmott-tuned Matchless speedway engine was a catalogued item: "Ample spares available at competitive prices," stated AMC's advertising. The Emmott-tuned motor incorporated a forged 9.5:1 piston while retaining the standard 7R-type crankpin, con-rod and flywheels. The magneto was bolted directly to the back of the timing chest, simplifying engine removal, and using an Amal Concentric carburettor and high-level megaphone exhaust system the motor produced a (claimed) 49bhp at 7,000rpm.
Bolted into Dural engine plates, the Matchless G85CS/BSA RRT2 engine/gearbox unit formed a structural member of the frame, which was constructed from aircraft-quality T45 tubing and weighed just 11lbs. The shortened R E Humphries front fork was fitted with a Dural top yoke, while braking was looked after by an 8" Jim Robinson tls unit at the front and a 6" British Hub Co item at the rear. The Greens moulded their own glassfibre 4-gallon fuel and 4.5-pint oil tanks; the latter originally installed, somewhat unusually, directly behind the cylinder barrel. All-up weight was a highly creditable 240lbs, around 40lbs lighter than a standard Manx Norton.
In the spring of 1967 the GB500 was tested by Motor Cycle's David Dixon who found its on-track handling "lighter than any other 500 I've ridden, with a sensitive feel and good directional stability." Motor Cycle's racer-tester also liked the engine's beefy low-down punch and ability to rev cleanly without 'megaphonitis', but reckoned the front brake overly powerful, this before the universal adoption of disc brakes it should be remembered!
The Greens had hoped that their prototype - the machine offered here - would be the first of a short production run, but their plans came to nought and this remains the sole example made. The machine was originally raced by 'works' rider Terry Sparrow, but its subsequent racing career remains unknown. In the early 1990s the bike was discovered by top restorer John Mossey - having been off the track for 20-or-so years - and completely restored by him. It was purchased directly from John Mossey's stand at the 1997 Classic Bike Show by the vendor, an enthusiastic classic racer and member of the CRMC. Used since then only for the occasional parade, most recently at Cadwell Park in 1999, it is presented in very good condition in every respect and offered with contemporary magazine articles and CRMC Registration Certificate for Group 2, Period 2. A relatively inexpensive way to go classic racing/parading on a unique and historic British racing motorcycle.