Cycle News - Archive Issues - 1980's

BiG BORE WEAp NS TItE bikEs of TItE ~cc NATioNAL MOTOCROSS CItAMpiONSltip By JiM GiANAYsis The 1980 motocross season in America has seen the technical aspects of the sport continue to evolve at a tremendous pace. Each year the major factory teams make great strides in both the design and development of chassis, engine and suspension components. And nowhere are these changes more exciting than in the SOOcc class, where brute dirt throwing torque, eye watering horsepower and increased weight all combine to make these monsters more than a handful that only a few top factory riders can control to their bikes' full potential. There are two significant changes affecting the four major J apanese brands' works bikes this season. One is an increase in the FIM 's minimum weight limit for 500cc class bikes in International class competition from 209 t o 224 pounds. While this weight increase won 't be imposed in American AMA motocross until 1981, the Japanese teams usually build their bikes to FIM specifications so most of the . bikes already comply or come close to the new increased limits. Yamaha OW 418 . 22 The other is the adaptation of single shock rear suspension systems now being used by all four major Japanese teams. Yamaha had pioneered the monoshock concept back in 1973 when its new Monocross YZ works bikes in the hands of Hakan Andersson won the 250cc World MX Championship, but the advantage was the increase in rear wheel travel the Monocross design offered over conventional ' twin shock bikes with short rear wheel travel, rather than any inherent advantage the monoshock system itself might have had. It wasn't until just last year, 1979, with Kawaski's introduction of their Uni-Trak motocrossers featuring variable leverage ratio suspension did a monoshock system offer any major advantage over conventional twin shocks. Honda followed Kawasaki at the end of the 1979 season with the introduction of Honda's own Pro-Link monoshock design. also employing VLRS. and nowthis year, Suzuki has stepped onto the racetrack as well with a VLRS monoshock design labeled the Floating Suspension System. box-section aluminum and has Kawasaki's trick eccentric rear axle adjustment system . Wheelbase on the bike is 156.Scm (60.0" and the KX tips the scales as the heaviest of the Japanese works bikes at 230 pounds. Last year the Team Kawasaki riders like Brad Lackey felt the KX 420 production type engine was just too slow , so this year the works riders are using a similar production based engine wh ich has been stroked out to 440cc displacement. The cylinder employs reed valve induction and Kawasaki's unique Electro Fusion iron coating on the bore of the aluminum cyli nder. Carburetion is by a 38mm Mikuni. And like the Open class works Yamaha, the KX 440 Kawasaki only runs a fou rspeed transmission. Former 500cc National Champion Rick Burgett's 46Scc works y amaha doesn't have any major changes this year, but it does have a number of significant detail mod ifications . Most of these are centered around the suspension where , up fro nt, there are massive new 43mm Kayaba air/spring ' forks for better stability and offer ing 300mm (1 2 inches) of travel. Yamaha's aluminum deCarbon reservoir shock for the rear Monocross suspension now has a two-stage tapered w ire coil spring, and together with the lightweight aluminum swingarm there is 310mm (1 2.5") of rear w heel travel. This year's OW 41B is a littl e light er than last year's A mode l by some two pounds despite the heftier suspension comp onents. This is brought about by Yamaha's use of titanium on their motocross bikes for the first time in a number of years, bringing the weight on the Open bike down to 216 pounds for American races. W heelbase is 156.5cm (60.0" ), The gas tank shape is changed to a design wh ich is taller in the front, but narrower on the sides for more rider leg room . Yamaha's reputation for excellent brakes is imp roved even more w ith the addition of a new double leading brake shoe assembly at the front wheel, w hile magnesium coni cal hub assemb lies also help to make Yamaha OW wheels the lightest. Rick's choice of tires are Pirelli w ith a 3.00x21 MT 25E Pentacross up front and a 4.50 x18 MT 25 out back. Model designation for the 465cc ,powerP!fl,l;l\ ' 04\ e.vviJtl ~jck r.eP9~ if1g that it puts out more horsepower over a broader power range than last year's. The cylinder uses ' Yamaha's sevenport design and has a chrome plated alum inum bore. The cylinder reed valve induction has its fuel mixed by a monster 40mm M ikuni carburetor . That this engine puts out a broad enough torque band is prov en by the fact the transmission only has four gears to propel it towards the winner' s circle. Kawasaki KX 440-80 The introduction of Kawasaki's UniTrak works bikes last year proved to be a major step in the advancement of I motocross rear suspension. By placing their monoshock (a coil-over Kayaba deCarbon reservoir shock) low in the frame behind the engine, Kawasaki lowered the center of gravity of their monoshock system substantially, compared to Yamaha's design, for bette r handling . More importantly though, Kawasaki's shock assembly operated off the swingarm by way of a rocker arm wh ich varied its leverage ratio 40 percent during rear w heel travel to provide a suspension w ith spring and damping rates w hich became progressively firmer towards bottoming out. Numerous teething problems on the new Uni-Traks hampered their performance last year, but a complete redesign of the bikes for the 1980 season has turned them into strong performers. Kawasaki test rider Goat Breker's KX 440 employs the new 43mm Kayaba air/spring front forks for 300mm of travel, w ith the rear wheel traveling . .an-.equal , amoum., TM ) t''/IIingqrlT\ Js Honda RC AlE W ith Kawasaki already having pioneered the w ay, Honda brought out their own idea for a VLRS wor ks bike at the beginning of the 1980 season. Called the Pro-Link, Honda's monoshock rear suspension offered some major imp rovements over Kawasaki's Uni-Trak, most notably an inverted shock for easier adjustability and a rocker arm assembly wh ich is an integral part of th e aluminum swingarm for increased suspension strength without the need for a heavily braced frame. This, in turn, helps reduce w eight and the Open class Honda RC is the lightest of the Japanese wor ks bikes at or near 209 pounds in America. Suspension travel on the RC bikes is 300mm at each end. The front-torks are I • Ij • , 1 II \ f ~.. II r I r I I ( , \:: I 1 ( I tubes. Testing on rear shocks continues at this time and depending on rider choice it may be either a Showa, Kayaba or Fox Factory coilover deCarbon type shock with remote reservoir. Wheelbase is also 60 inches like on the other Japanese team bikes. Engine displacement on the Open class RCs is a closely guarded secret, but it is pretty certain that American Honda riders Chuck Sun and J im Gibson are running 450cc motors wh ile European riders like Graham Noyce and Andre Malherbe favor the even larger 496cc versions. Chrome bore aluminum cylinders have reed induction and are fed by 38mm Keihin carburetors. The sand cast magnesium engine cases house a four-speed transmission and are designed so that the Hondas remain the only motocross bikes with externally adjustable ignitions - just the removal of a screw typ e inspecti on plug is required to check the proper alignment of the timing marks. Suzuki RN 440-80 Suzuki is fairly cautious w hen it comes to trying new ideas, but once they saw th e trend turning towards monoshock rear suspensions it wasn't surprising that before long they would introduce a VLRS system of their own. Called the Floating Suspension System, the new Suzuki monoshock proved themselves successful in the first Nationals and Grand Prix they were entered. Similar to Kawasaki's Uni-Trak with a .high frame l]'lOunteo rocken arm 855efTl-

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