International Dragster

International Dragster

A Czech Grasstrack Engine Burns the British Quarter

BRUCE COX

TWIN CYLINDER engines have such a stranglehold on 500-cc drag racing that it’s difficult to imagine any other type in the act -least of all a pushrod Single! However, British drag racer John Henderson, a 25-year-old toolmaker who lives at Coventry, where Triumphs are manufactured, has blasted into the act with an engine used by no other drag racer in the world! The powerplant he uses is the single-cylinder, Czechoslovakian ESO—the engine used to power such diverse bikes as Class A speedway rigs, ice racers, and sand and grass track competition machinery. The engine is quite easily obtainable in the U.S., as it is manufactured by the well-known Jawa-CZ concern.

The engine is one of the Continental grass track units that power spindly bikes around smooth three-quarter-mile ovals at over 100 mph. Eitted with S&W valve springs, engine speed is over 8000 rpm. Bore and stroke are 88 by 82 mm, respectively. Henderson uses a small reverse cone megaphone exhaust, similar to that employed by the works grass track riders on the European circuits.

To the neat chromed frame Henderson has added the extra weight of swinging arm suspension, instead of the rigid configuration, because it insures more predictable take-offs and straighter runs on the strip.

Tiny brakes are fitted at either end, a Suzuki 80-cc unit at the front, with a conglomeration of Vincent, Erancis Barnett and Velocette parts at the rear. Another reason for swinging arm rear suspension is that experimental wheelbase alteration is much easier.

The swinging arm is built with an adjustable pivot. Henderson had the unit made this way after the bike completely flipped on the line at one drag race. He decided that wheelbase alterations perhaps would be a good idea.

The front fork is made to Henderson’s own design and weighs only 8 lb. The unit is a simple pair of tubes and sliders with dural bushes, and a single, centrally-mounted damper.

Henderson uses 18-in. wheels, with a 2-in. section front tire, and a wide slick on the rear. A full dustbin fairing is used. All-up weight, including the engine and the Norton gearbox, is about 180 lb.

While he was saving for the expensive ESO engine, Henderson used the bike with a 500-cc JAP Class A speedway powerplant. The two are virtually interchangeable. His best times were in the 13-sec. bracket.

As soon as he changed to the I SO. and running only straight methanol, he clocked 11.88 sec. By adding 40 percent nitro, he whittled the time down to 11.4 sec. And, it appears that times will become even lower as the machine gets more and more race developed.

Henderson found the ESO requires a completely different riding technique than that used with the JAP, though the frame is the same. With the JAP in place, he was forced to sit well forward in order to keep weight on the front end, as the rear tire bit. The ESO produces much more wheelspin, so now Henderson must sit well rearward in order to hold slippage to a minimum a good reason for wheelbase alteration!

Henderson doesn’t use wheelspin as a deliberate getaway technique. He finds that the power characteristics of the ESO are such that clutch slipping produces lower times.

And, he certainly proved his point. The bike has scored numerous class and eliminator wins on British sprTnt and drag strips, making the Czech-engined machine one of the bikes to beat in the British meets.