Cycle News - Archive Issues - 1980's

Cycle News 1980 04 16

Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles

Issue link:

Contents of this Issue


Page 1 of 47

- .... 0.. < $-< You can buy .Imost everything pictured here from S.J. BMW. S.J. BMW has fewer beans. better handling than fours. The last of the big boomers? By Pat Eagan ose San Jose BMW acquired an ex-factory racing Beemer from Butler and Smith late in 1977. Their intent was to go racing, learn their lessons, and use the knowledge gained to provide better service and parts for their custorners. Almo~t ~very. part used on the race bike IS available either as part of a "Handling Kit" or a "Performance Kit." 16 h' I II They leamed t e!r essons we enough that Harry Khnz?,ann won th.e f~1I 1978 Loudon NatIonal on thIS blke_ Harry placed well enough 10 t.he other ~allonals that year to fimsh ~ourth ,.n the .champlOnshlp, Another Impr~lVe finosh for the team was the 250-mlle endurance race at Se~rs Pomt that year when Harry and DaVId Emde rode the bIke to first overall. Own~r Ron Lang and serv,,:e manager Chns Hodgson are the maIO people behmd the p r o J e c t . . . One ?f the most ,mport~nt mod,ficallons. In the search for rehable. horsepower IS the rol~er tappet cam kIt. The case~ ,are machmed to accept Harl~yDaVIdson XR75? roller tappets whIch work agamst e'ther Erson, Isky. or Crane camshafts. S":'llh Bros. chromoly push rods act a~amst stock rocker arms. Manley stamless steel valves are c1~ by Sig Erson springs and titanium retamers. Inlet valves are 2mm larger than stock a,:!d ,the exhausts ar~ Imm smaller, for .,mproved flow, A,r and fuel mIxes on the 40mm Del Lono carbs and the exhaust exits through a set ofC.R. Axtell megaphones. Venolia for~ed slipper pistons have a Dykes top nng and provIde a compressi~n ratio of 12.2: I. To improve cornenng clearance, the barrels are . 38mm shorter than stock. To accommodate this, the' steel Carillo rods are 10mm shorter than stock and the wrist pin placement of the pistons is 9mm higher than normal. The crankshaft is cross-drilled for better lubrication, polished, lightened and balanced, Power is delivered through the Borg & Beck sintered bronze clutch to a close-ratio four speed. The stock five speed trans is too fragile to handle the increased torque. Nine different ratios are possible althe ring and pinion, As per Superbike rules, the charging system is removed, leaving the bike with a total loss ignition. A Krober ignition designed for a 250cc Yamaha has b~n adapted, providing troublefree, zero maintenance. It is a CDI system which fires Champion N57G plugs through Accel wires and plug caps, The two-spark plug-per-cylinder arrangement is reported to yield improved midran~e performance. Although the handling of the average BMW is quite excellent. the crew at San Jose BMW found many areas where they could improve the stability and tautness of the chassis, To improve the rigidity of the forks, S. J. BMW manufactures their own top clamps, and fork and fender braces. The top clamp is a machined billet of 6061 T-6 aluminum and the "tweak bar" fork brace is also aluminum. The fender brace is made from chromoly tubing and TIG-welded. The biggest gain in chassis stability was attained -by bracing the swingarm with chromoly tubing. This is ne<;essary because the driveshaft and ring and pinion are trying to twist the swingarm into the shape of a pretzel. In between, the frame has had tubing installed from the swingarm pivot to the front downtubes. The rear sub-frame and shock mounts have been braced and the top engine mount is now chromoly tubing. Bucl1anan's laced D.LD rims to stock hubs using eight-gauge spokes. Rim sizes are WM4-18 front and WM6-18 rear, mounting Goodyear 3.25x18 and 3.75x18 tires. Braking is accomplished in the front by Lockheed master cylinder and calipers acting on Kosman 11\4" cast iron rotors: Standard rear drum is used. Ferodo lining is used front and rear. Fluid passes through stainless steel brake lines. Riding the Beemer was a very plea: surable experience for me and yet strange at the same time. The twin cylinder bike is very manueverable and light, showing itself to be superior in a series of esses to a four cylinder bike. Steering is very neutral with no tendency to fall into the turn or steer wide. The keynote to this bike would have to be stability. Even so, the strange part comes from the torque reaction of the dn'Veshaft and the longitudinally placed engine. When blipping the throttle in neutral. the bike rocks back and forth from left to right. Once underway, the torque reaction is not so noticeable but rise and fall of the rear end is a new experience. ·When you back off the throttle, the rear drops, and when you apply throttle, the rear rises. One positive note here is that when you lean the bike over and the rocker covers touch the pavement, extra ground clearance can be gained by rolling on throttle. Thus a technique must be mastered of using throttle and brakes simultaneously through the turns. I rode the bike at an AFM race at Ontario using the backward course. The bike was at its biggest disadvan- tage here because you exit the infield already at high speed and continue accelerating down the front straightaway. The top end speed of the modified four cylinder bikes shows up here. When Harry Bresach waved the green flag, 1 released the clutch at the same time as the other guys but the superior acceleration of the fours left me looking at the taillights of about eight bikes. On the second lap, I passed Chuck Parme for the lead through a sw~ping left hander in the infield. We raced back and forth for two laps until he was blackflagged because of an oil leak. My glory lasted for one more lap until I saw the oil pressure gauge take a dive. Chris and Ron and I discussed it and agreed that we lost pressure because the sump was half a quart low. Ron went out in the next race and rode for eight laps with no problems. With the continued development of the four cylinder bikes from Japan, no twin cylinder has a chance to win anymore at an AMA National where the track has a straightaway of any length. Next year. the AMA is trying a split displacement formula for Superbike Production with the fours getting 750cc against the twins' 870cc. One of the beauties of Superbike used to be the fact that so many different bikes and riders were cilpable of winning. Experimenting with a split displacement formula in the Formula I class at Daytona this year generated much enthusiasm because now something other than one brand was capable of running at the front. Also, split displacement formulas are not new to the AMA as it used to be 500cc OHV against 750cc flatheads. This reponer is looking foward with anticipation to next year when once again BMWs, Moto Guzzis, Ducatis. and Triumphs can be competitive with Hondas, Suzukis, Kawasakis, and Yamahas. •

Articles in this issue

Archives of this issue

view archives of Cycle News - Archive Issues - 1980's - Cycle News 1980 04 16