Retrospective: Rokon RT340 Automatic: 1973-1978
October 17, 2011
Filed under Retro + Vintage Motorcycle Reviews
photography by Ralph Noble
[This Retrospective: Rokon RT340 Automatic: 1973-1978 was originally published in the July 2011 issue of Rider magazine]
Here’s your barroom bet question: What was the first motorcycle (not scooter) to have an automatic transmission? Nope, not the Japanese Honda CB750A of 1976. Nor the Italian Moto Guzzi 1000 Convert of 1975. It was the American Rokon RT340 of 1973, a street-legal single that was designed as an enduro competitor.
All the rider had to do was twist the throttle and go. No changing of gears, no slipping the clutch, just keep the two-stroke single wound up, and this 280-pound machine could go places…within reason. A little over three gallons of gas in the fiberglass tank might take the leisurely rider 100 miles—a good deal less if speed were a concern. All this without ever having to move the toe of a boot up and down. An odd feeling, that must have been, for any rider coming off a Honda XL350 or Kawasaki F9 350.
Rokon might not be a name on every motorcyclist’s lips, but the company has been around for almost half a century. It began in California in the late 1950s, when a bright light by the name of Charlie Fehn came up with the notion that a two-wheel drive motorcycle, with big, squishy tires, could go just about anywhere. He was riding a prototype over the sand dunes in 1959, and soon went into producing the Trail-Breaker, using a West Bend 134cc engine and a three-speed Albion gearbox. Not a dirt bike, not a dual-purpose bike, but a rugged machine that could dawdle through unroaded back country effortlessly, climbing unclimbable hills, traversing great expanses of muddy terrain, crossing miles of loose, soft sand…all without requiring too much expertise from the rider.
Homely was rather a kind word to describe the Trail-Breaker; useful, yes, attractive, no. The tires were fat ones, 8 x 12 inches, knobby agricultural things mounted on wheels that were hollow 4.5-gallon drums. When empty, these drums were useful for floating across a river, when filled with fuel they could provide a full day’s riding without need of a gas station, or filled with water, fight a fire.
Sales were good, but Fehn soon lost interest—he was more into inventing than production—and in 1963 sold the whole kit and kaboodle to one Orla Larsen, a successful distributor of the Trail-Breaker in New England. Larsen decided on the Rokon name, and in 1970 substituted a Salsbury torque-converter for the Albion gearbox, creating an automatic transmission. Buyers loved it.
The success of this model created a desire in the company to build a real motorcycle, a competitive one good for trials and enduros, using the same principles. A number of efforts were made to create a more sporting version of the Trail-Breaker, but none came to fruition, as the machine was just too ungainly. But the engineers felt that the automatic tranny design had a future in the dirt-bike world.
Fresh sheet of paper. Drive train first, chassis, second. Need a bigger engine. Sachs had a nice one, used to power snowmobiles, a 334cc two-stroke single. It was a four-port engine—intake, two transfer, exhaust—along with two booster ports which helped send the mixture toward the exhaust, creating a better burn. Built tough, it had the crankshaft running on ball bearings. In ’73 Rokon used an American Tillotson 38mm carburetor, but soon found a 36mm Mikuni worked better. Compression ratio was said to be 11.2:1, using the European full-stroke measuring system, whereas the Japanese exhaust-port measurement would read about 7.2:1—quite a difference in numbers, not compression.
Starting this engine was a new experience for riders, as it used a pull rope—like on a snowmobile or lawnmower. Various starting techniques were developed, one of the more popular being to stand on the left side of the bike, left-hand reaching across to the right end of the handlebar, keeping the throttle closed and the front brake on, right hand grabbing the T-handle on the end of the rope. Pull! It might take a few pulls when cold, usually one pull when warm. Once running, if the rider wanted to “cleanse” the engine with a bit of a rev, he could lean the bike onto the sidestand, lift the rear wheel off the ground, and rev away.
Throw a leg over the saddle, twist the throttle, and the torque converter was intended to start functioning at about 2,800 rpm. The more spin, the more centrifugal force, the harder the bite, with the engine designed to turn happily at a competitive 6,000-6,700 rpm all day long, maximizing the torque automatically—so to speak. Rokon said the engine put out 37 horses at the crankshaft, figuring about 30 at the rear wheel. A normal dyno test was not possible, as a compensator in the “tranny” always adjusted for rear-wheel load. Conversely, when the throttle was backed off, the RT was in free-wheeling mode…no compression braking. A #530 chain went from a 13-tooth counter sprocket to a 54-tooth wheel sprocket.
The chassis was quite conventional, the drivetrain sitting in a cradle frame made of steel tubing, with a wheelbase of 57 inches. The Spanish company Betor supplied the fork and twin shocks, the fork being raked at 30 degrees with trail of 4.7 inches, the shocks having three-way preload. Tires were a 3.25 x 19 knobby at the front, 3.50 x 18 at the back. And hydraulic disc brakes at both ends used single-action calipers and 11-inch discs; brakes were important because of the lack of engine braking.
Good saddle for the solo rider; no passenger pegs offered. On top of the triple clamp was space for three instruments, with a speedo/tripmeter, watch holder and an enduro route-chart holder. This was certainly intended as a competitor for the International Six Days Trial, which just happened to be held in New England’s Berkshire Hills in 1973. The RT did itself proud, with four medals. And all this for $1,645.
Rokon had spent, and was spending, a lot of money on developing the RT, but the factory justified it by taking more medals in the 1975 ISDT. In 1976 the RT340-II model came out, with some minor mods and a $250 price increase. But the company was headed for bankruptcy and receivership…which came about late in 1978, with some people blaming the RT.
In 1981 Rokon went back into business with new owners, making various models of the Trail-Breaker. But no more RTs.