blank 01/09/12 02:51PM Dirt Bikes, Enduro Bikes, Off Road, Off Road Racing

Vintage Dirt Bikes: A Look at Rokon Automatics

Feb. 15, 2011 By Dan Paris

Mike Murphy’s beautiful ’76 Rokon Cobra 340 motocrosser.

Mike Murphy’s beautiful ’76 Rokon Cobra 340 motocrosser.

Murphy still races his ’76 RT-2 in vintage events, riding it just as hard now as he did back then.

Murphy still races his ’76 RT-2 in vintage events, riding it just as hard now as he did back then.

It seems, with only a few exceptions, that not much is new to the dirt bike world. Bold new graphics, sure. Fuel injection is “sort of” new but dirt bikes have been developing that since the early ‘90s and airplanes had fuel injection before WW2. But 1970 was different. The dirt bike market – and subsequently, technology – was expanding at an unprecedented rate. You name it, they’ve tried it. Perhaps the most radical of all the early ‘70s designs came from a little company in New Hampshire more famous for building unstoppable two-wheel drive ATVs.

Rokon’s weird two-wheel drive Rokon Trailbreakers were one thing, but when Rokon decided to cash in on the expanding dirt bike market things got really strange! The radical machine they came up was a clean-sheet dirt bike design. Remember, this was an era of pipey, piston-port two-strokes with hand-grenade reliability. Motocross riders had to be clutch artists, constantly tap-dancing the shifter just to keep the engines in their narrow powerband. Hop off a modern bike and onto a vintage motocross bike and you’ll instantly develop respect for pro riders of that era!

Instead of fighting that battle Rokon used a simple, reliable 340cc Sachs snowmobile engine. Transmission? What could be easier to use than a snowmobile-style Salsbury clutch? Twist and go. With an infinitely variable transmission Rokon engineers didn’t have to worry about a peaky powerband and could instead tune the engine for maximum power and simply adjust the clutch to keep the engine revving at the power peak all the time. A great idea, in theory at least, but would it work on a dirt bike?

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