Cycle News - Archive Issues - 1970's

(Left to right) Jim Gianatsis discusses the works Yamaha QW-38-B with tuner Keith McCarty and Bob Hannah. Riding a winner Bob Hannah'sOW-38-B 810Yamaha By Jim Gianatsis Keith McCarty, Bob Hannah's mechanic, checked the hand formed aluminum tank to see if it had enough fuel. It did. My palms were already sweaty as I jammed fingers into wrinkled up gloves . Nervous . wasn 't the word for the way I was shaking, but I tried to hide it, pretending that I was.headed 16 out for a trail ride on a production bike. "Do you want me to start it for you?" "Ahhh.. .no t ha nks. It shouldn't be any problem." Boy, was I acting cool. A sure sign that I was going to blow it . I swung a leg over t he saddle and right away I knew I was in trouble. I couldn't find the foot peg on the other side . My knee was perched over the saddle almost level with my helmet visor. The bike was too freakin' tall to sit on and start! I dragged my leg back over and off_ the bike. Pushing it over besid e the wooden box Keith uses as a centerstand, I used the box as a step to get up on the bike, reaching the foot peg and th e kick sta rt er on the other side. " PP PL LLUUT.. . PPP LLLUUT .. . PPP LLLUUT .. .' · Now it wouldn' t crank. T his thing has a kick starting ra tio like an old Husk y and the internal rotor COl flywheel wasn 't helping matters a ny. " Kick it hard right from th e top of the ' stroke and follow all the way through." . " BBRRRAAAATrTTAAAA TIT· TAAAATrTT." That d id it! Just breathing on the shift lever with the plastic boot snicked its gearbox into first and with an easing out of the clutch and a slight increase in he ight of the Mikuni's slide I was underway. The bike is the most exotic and most expensive in ' the history of motocross. It's Bob Hannah's National Cham pionship and Supercross winning OW38·B 810 worlts Yamaha . More exotic, because it contains more inovative ideas a nd on e-off han d fabricated pa r· ts than an y other fa ctory works bike ever buil t . More expensive, beca use engineering new id eas costs lots of money a nd there are less of these OWs around than RCs, KXs a nd RH /RNs to m ake th e per unit cost of the OW mu ch higher. But how much highe r? Everyone likes to d iscuss th e p rice of works motocross machinery, though the re's no real way to figure out all the m an a nd mach ine hours involved in d esign and const ru ction . Still , for those of us, myself inc1uded , who like to entertain thoughts of wha t sand cast magnesium cases and acid dipped progressive rate springs all cost , there are rough figures available. Six years ago Suzuki used to advertise that their works bikes cost approximately $30 ,000 . So take that figure , double it to cover the rise of in. flarion (remem bering what Datsun 240 -Zs once cost) , and then double it again because you're dealing with an all-new and more complex des ign in the OW-38 -B 810. (fyour calculations come out to $120 ,000 like mine did , we probably aren't too far from reality. So there I was riding off to test a works Yamaha that m ay hav e cost in excess of SI 00 ,000 an d th e last th ing Keith said to me before I d umped th e cl u tc h was , " Do n' t wo rry a bou t breaking it. I ha ve to reb uild it this week anyway." Those last few wordsmade me ' feel • ~ " '" - • ~ • • I I not so bad when I dropped the bike on the first lap of the mud slick downhill test track Hannah uses when he is on the east coast. The rear brake is really powerful and combined with marginal traction to the ground and light flywheel momentum 1 had insta n tly stalled .the engine, low sid ing the bike and snapping off the clutch lever . I watched Bob do the same thing in the same place th e day after, only he had the proper reaction to pull in the clu tch and let the rear tir e freewheel instead of slide. He did overshoot the tu m at the .bottom of the hill , but he didn't crash like I d id . Such is the skill of America's top motocrosser. Yamaha deserves a lot of credit for such an inovative des ign as the monoshocker and in particular, the . latest OW·38 (250cc) and OW-39 (400cc) works designs which have put them back in the winner's circle with Bob Hannah and Heikki Mikkola. On Bob 's OW-38 -B 810 the B designation means there is a redesigned frame among other changes on th is model , and the 810 signifies the bike was completed at the factory on August 10th of last year . Though they haven't always been obvious, Yamaha has had a number of major revisions on its works bikes since the first YZ·250B monoshock of Hakan Andersson won the World Cha m pionship in 1972 . The engine, monoshock unit and frame have all undergone at least two complete redesigns on the big bikes since then, and Hannah's OW·38 is a totally new machine, not reworked versions of the OW·26 and OW-27 which failed him in his bid for the 250cc and Open National Championships last year. This year's engine is a new design with more compact sand cast magnesium cases to house the 6·speed transmission. It still looks somew hat bu lky, but weight is reduced. Yamaha stays with their proven 70mm x 64mm bore and stroke ratio that allows an undersquare engine of 246cc. The cylinder is also typical Yamaha with a center exhaust port and Torque Induction type reed valve being fed by a 38mm Mikuni carb o The aluminum cylinder is chrome plated in the bore, th e advantages of which are less weight, better heat dissipation and less wear. Early GYT kit Yamaha DT's and YZ's had chrome cylinders, but such exotica despite its advantages isn 't popular with th e public. The con seque nces of un ch anged ai r filters or over revved engines aren 't as expe nsive if you ha ve a steel sleeved cylinder liner to rebore each week. Another po int whe re the new engine d iffers from a typical production engine is the powerband. The OW· 38's porting has been d esigned for low and mid-range power. Under 6 ,000 rpm it pulls like a freight train, but once you a p proach 7,000 rpm you're wast ing tim e not being in the next higher .gea r. In fact , it almost bogs hard enough to pitch you over the bars. Peak horsepower is probably less than any production 250cc now on the market. What makes the OW-38 competitive , t houg h , is the .wid e usable power range between 3,500 and 6,000 RPM , with the engine actually capable of pulling without bogging from as low as 2,000 rpm. The internal rotor COl helps to make the engine instantly responsive, but you have to be careful on uphills and braking for turns not to kill the engine by backing off the throttle too hard . The engine begs to be short shifted because of its low RPM range, while acceleration out of tight turns can be. compe nsa ted for with H annah's favori te techniq ue of fea the ring th e clu tc h so the bike litera lly ju m ps. Beca use t he powerba nd is so easy to control, the bike is obvio usly com : " t " I ' ''' J I • • r

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