In 1963, the AMA decided that the 500 cc Matchless G50 wouldn’t be allowed to race in the U.S. as it wasn’t a street bike. This reversed a 1961 vote that had given the G50 a pass and was particularly upsetting to Dick Mann, who won the Grand National flat track plate riding a G50.

Matchless built only 25 scrambler examples of the overhead-cam racer to meet the requirement of street legality. The result was the Matchless G50 CSR, also known as the “Golden Eagle”. This is one of the most valuable bikes to bear the Matchless name.

Any films of motorcycle racing shot in the 1950s or 1960s might lead you to believe that the Norton Manx was the backbone of British efforts, but both AJS and Matchless fielded simpler overhead camshaft bikes with much success. It was actually these bikes that Honda basically copied for their own GB500 single.

The 350cc AJS 7R “boy racer” first appeared in 1948 and proved a match for the Norton 350cc Manx, which was basically a 500cc bike and almost 50 pounds heavier. With a chain-driven, overhead-cam engine, the 7R made extensive use of magnesium engine castings, gold-painted for protection. Much work could be accomplished while the engine was in the frame, which delighted privateers. By the time the last one left the factory 15 years later, 700 had distinguished themselves in every class for which they were eligible.

The real stroke of genius, though, occurred in 1958 when the 7R engine was enlarged to 500cc and the Matchless G50 was created. A total of 180 G50s (for 50 hp) were built over the next four years, according to author Mick Walker, and the bike proved instantly competitive as it weighed barely 300 lbs – the same as the 350cc AJS.

Dick Mann almost won the G50’s U.S. debut at the Daytona 200 in 1962, finishing ten feet behind Don Burnett on a works Triumph. Mann also raced the G50 on flat tracks with a BSA Gold Star rigid frame. The BSA frame was eventually banned, so he finished the season on the 7R frame in both categories. This made him the first man to race a bike with suspension on flat tracks, and he took third place nationally after a crash at Springfield cost him the coveted #1 plate.

This kind of success upset the so-called “iron triangle” of BSA, Triumph and Harley-Davidson and a protest was filed that the G50 was not a street bike, which the AMA demanded for production racing. As a result, the AMA banned Mann from the 1963 Daytona 200, though unaccountably he was able to ride flat track with the 7R racing frame and actually won the #1 plate that year.

While the road racing protest wound its way through the AMA system, Matchless thought it had solved the problem by creating the street-legal CSR, cramming a version of the high-revving G50 motor into the G80CS Scrambler frame. Lights were powered by a belt driven generator, a smaller carburetor was fitted and a larger muffler. The overall effect was handsome but the bike didn’t run all that well. The carburetor and muffler combination reduced the engine’s airflow to wheezy inefficiency.

Total production of the G50 is thought to have only been around 100 bikes. The AMA allowed G50s to race again in 1964, but the main threat to the CSR scramblers’ survival was their owners, who cannibalized them to keep race bikes going.

The Matchless G50 engine proved bulletproof and was raced competitively through the 1960s, first in the hands of Tom Kirby’s team, then Colin Seeley, who bought out the Matchless racing department when the company quit in 1965. The engine was developed until in 1970, Tommy Robb brought his own bike home 4th in the 500cc World Championships against the factory teams.

Japanese two-stroke race bikes eclipsed the Nortons and Matchless singles in the 1970s but the British bikes had their revenge when they became eligible for vintage events and, with new technology, have proved extremely competitive.

The biggest issue with buying a G50 CSR is finding a real one. Frame numbers don’t mean much, and engine numbers only identify the model and year. Since race bikes were made at the same time and G80CS Scrambler frames occasionally turn up, provenance is everything.