That ‘70s Bike: Rokon VMX Bike Build, Part 1
It’s no secret that I’m drawn to weird motorcycles, and weird is a word that describes Rokon’s 1970s line of automatic transmission dirt bikes perfectly. Off-Road.com did a feature story about Rokon a while back, where we learned about their ideas and their racing success before the New Hampshire-based company fell into financial trouble.
Although I’ve always been interested in Rokons and had seen them often enough I had never actually ridden one. The father-and-son team of George and Tom Canellos race a nice 1975 Rokon MX340 in vintage motocross, most recently with Tom (pictured aboved) getting two holeshots and back-to-back moto victories in the 1966-1975 Amateur class at the Ormstown Vintage Off-Road Festival in Quebec, Canada.
Earlier this season Tom had raced against the newer bikes of the Evolution class just for kicks, embarrassing the field by getting the holeshot in both motos. It was at this race I had my first chance to ride a Rokon. George came up to me after the races and generously offered to let me try his bike, along with warnings about lack of engine braking. Within a few corners I was comfortable, carving laps at least as fast as I had on my ‘75 Can-Am! The Rokon pulled hard, handled ok and had real brakes! Best of all it was easy to ride fast; just pin it wide open like a snowmobile and let the Continuously Variable Transmission do all the work. I was sold! I had to find one of my own!
Wanting a Rokon and getting one are two different things. There never were a lot of them made, at least by Japanese standards. Mike ‘Rokon’ Murphy of Rokon Renew (you can email Rokon Renew at firstname.lastname@example.org) kept his eyes open for me, eventually finding a restorable and affordable 1976 RT-2 340 which he brought to me at Ormstown. Murphy also provided Rokon owners and parts manuals, some spares and tons of tech advice on how to make Rokons fast and reliable. Murphy’s, Canellos’ and my own Rokon became the talk of the Ormstown pits! The goal of this project, like with my Can-Am build, is to put together a competitive and presentable-looking vintage race bike but not a garage queen I’m afraid to get dirty!
Murphy went on to place second in the 1976+ Expert Class in the Hare Scramble at Ormstown, all the while with his Rokon sounding like a snowmobile gone berserk. I was busy racing the Off-Road.com Can-Am project bike, so while I couldn’t wait to tear into my own Rokon I knew it would have to wait until I got home.
I wasn’t home for an hour before I started pulling the Rokon apart. Every inch of the bike was fascinating! The bike is solid too, which is something to be said for quality American materials and craftsmanship. Then again the Rokon is also quite agricultural, with cobby bits and lots of places where 10s of pounds could be carved off. Why the factory didn’t do that in the first place is kind of a mystery. The Rokon’s claimed weight is 250 pounds dry, and it feels about the same weight to lift as my new 450F… that means it’s probably about 40 pounds heavier than my ’75 Can-Am.
The Sachs 340 engine is a simple piston port two-stroke with a points ignition. Murphy had already changed the crank seals and installed a fresh top-end. Water had entered the ignition cover in Quebec, so it took a few minutes to clean up the points and get spark. I also removed the float bowl to check the float height and to make sure the jets were clear before trying to pull-start it. Fresh gas and three awkward yanks later and the Rokon fired up, settling down right away to a nice happy idle! The aluminum box you see behind the crankcase is a gear-reduction unit, but the Rokon still uses a giant 60-tooth rear sprocket. Also notice the cleverly designed rearward facing rear brake pedal and Kelsey Hayes rear brake master cylinder. I used to work as a Harley mechanic and found lots of familiar things when I started working on the Rokon.
The Rokon ran well but I was afraid to actually let it move under its own power until it had working brakes. The old callipers and master cylinders were seized, and the machine was missing both brake lines. I had visions of the engine revving up and the Rokon taking off across the yard right through the garage wall … I’ve seen snowmobiles do that and it’s never pretty!
The aluminum rims and the hubs were in good shape but most of the spokes were seized, breaking with the slightest touch of a spoke wrench. I’ve installed new wheel bearings, which were the same ones my Can-Am uses, and have been searching for the proper length spokes. I found a handful of front ones at a local shop, but the rears are proving to be more of a challenge.
The Rokon’s airbox is crude-looking fibreglass. I repaired some cracks with my trusty UV-Cure surfboard repair kit before treating it to a fresh coat of white paint and a sticker from my VMX racing sponsor Vintage Parts 4U.
The rear shocks don’t leak and seem to stroke smoothly, so we’ll leave them alone for the time being. The grease fitting on the swingarm is a nice touch, but the tunnel and skid bars running under the engine to protect the low-pipe are definitely overkill! Everywhere you look on the Rokon you see evidence of creative, but unusual, thinking.
The original air filter was falling apart, so a new round Uni-Filter and cage was shortened to fit snugly into the airbox. It’s easy to remove for cleaning and seals perfectly! Thanks Titan Cycle http://titanracingworld.com/ for helping me to find a filter that was such a close match!
Most of the Rokon racers I’ve spoken with have swapped to a more modern and serviceable Comet CVT, but after cleaning and inspecting the original Salsbury CVT I think it will work fine. My bike came with two other Salsbury primary clutches, and a friend of mine who was into snowmobile drag racing in the early ‘70s says we can tune the Salsbury to work very well. So we’ll try that first before going to a Comet unit.
Both master cylinders and brake callipers were easy to rebuild once 35 years of crusty gunk was cleaned out of them. Seaway Hose and Hydraulics http://www.seawayhose.com/ built the new braided stainless steel brake lines for me while I waited, and for the very reasonable price of $40 each! On Rokon Mike’s recommendation I used DOT5 Silicone brake fluid. I bled the brakes carefully and bingo, I had solid, strong brakes! Because of the CVT there is zero engine braking on a Rokon, so powerful binders are a must!
There’s a vintage motocross race coming up at Gopher Dunes in mid-October, so I’ve set a goal to make the Rokon at least presentable (and hopefully raceable!) by then. The forks are similar to the Betor forks used on my Can-Am, so I’ll be changing seals and servicing them soon. I’ve also been busy sourcing spokes, replacement plastics and other goodies like a lighter silencer. I’d love to find a narrower Rokon MX fuel tank to use, since the boxy RT-2 enduro tank is wide and horribly discoloured.
Because the Rokon was made in the U.S I am trying to rebuild this bike using as many domestically produced parts as possible. I’ve even been speaking to Titan Cycle about doing some cylinder porting and perhaps building a better pipe for the Rokon, like they did for my Can-Am. One thing for sure, this unique project bike will be fun to build, fun to tune, fun to race and fun to improve! Oh, and it will draw a curious crowd wherever I take it. Guaranteed!