Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126516
Close-up H '. NS750 .... y-twindirt ~ l!') $00 c:l.c. < tracker By Chari.. Moray Historically, AMA Grand National Championship Series racing has produced beautiful, homegrown machinery, assembled in dealers' shops, backyards, garages and in vans rolling through the night toward races several states distant Long boon of labor under the 'feeble gIim_ . mer of 60-watt bulbs gave birth to handbuilt raccbikel that first saw the light of day wben the YaII doors 14 nrung open at IOIIlC midwestern fairground. The ofren jewel-like, IllUdimes cobby motorcycles rolled down the ramp, out onto the track to win c101Cfought races. Honda, historically .has produced racing machiDcry in the mold of exotica personified, cast, forged and extruded &om the basic aI\oyI into World Championship-winning .GP bikes. Emerging from the best engineering minds jar.an has to offer, expedited through b ueprint stages into modern machine shops, motorcycles with as many cylinders as gears were created to win races, period. Some things never change, and in the case where Honda decided to go dirt trawng, the best of both worlds has been utilized. One of the best things to be taken from the American school is the talent of jerry Griffith. Griffith has been inwIved with dirt track racing aincc the early '60s when he tried his own hand at racing. He went through a stint working with Kenny Roberts in the mid-701 and on to Team Honda in '79. The finished motorcycle you see here is to a very large extent his brainchild. The CX500 motors were modified in japan at Honda R&D; the frame deaigned and built by Jerry. Then he put the rwo together and added the finishing touches. Bascially, the NS750 is a watercooled, four-stroke, four-valve V·rwin. Sounds simple. It isn't. Boosting the mild-mannered CX500 V-twin to a flame-throwing 750cc raeing motor was a trick in itself. The stroke has been lengthened with a new crankshaft, and the cylinder castings have been stretched to match by slipping a spacer in berween the head and barrel before slccving the whole deal. A heavier flywheel has been added to the countershaft side, and once that was put on, an outboard bearing became neccsaary to support the extra rotating weight. This whole pl'OCCSl rc- quired a DeW sandcast aide .cover. Enter the Japanar mega-y= touch. The frame/swingarm had to be ~de to wort over what became a very wide motor. Enter American ilJ8elluity. Griffith's cxpcriCIICC in the dirt track frame buaincsa told him how to weld up a suitable web of tubing to control the anticipated borsepower and deliver it to the ground. Cantilevered Works Performance shocks are presently being used to handle the estimated 78 bhp at 8,000 rpm. ThOlC horsepower figures, by the way, are not up-to-the-minute. Ex· haust pipes of different diameters are being tested, and the smaller, newer one seems better. The dyno test was done on a larger set. Predictions range around 85 bhp potential. Freddie Spencer and jeff Haney first rode the NS750 bikes at Aacot on Arril l! in preparation for the Afri ! Gardena Gold Cup. Two sets 0 forks were being tried, a set of Marzocchis and a pair from the Honda parts bin that originaUy were designed to hold up' the front end of an XRl!OO trail bike. Two sets of carburetors were tried on the bikes, a set of Lcctrons on Freddie's 119 machine and a pair of Del10rtOi on Haney's 128. Grimea disc brakes were fitted to each machine, Spencer's set up with the floating an· cbor rod below the swingarm, Haney's with the rod above. Track preparation for the half mile and the following night's National IT had not yet begun, and the Aacot oval refused to shape up despite a hurried grading and a once-over by the water truck. As a result, the racing surface allowed no indication of what could be expected for lap times on the aU-new machines. The combination of poor traction and the apparent power developed by the water-cooled twin left long rGOItertaiis hanging behind the riders on the straightaways. Sliding back on the seat only brought on a severe tendency for the machines to wheeliel Spencer totally erased the tread pattern from the left side of his rear tire. Both riders were obviously excited by the strellJ[th of the motors. When they're completely dialed in ... HarleyDavidaon, watch out! • Compllc:eted but cleen. the 119 T_m Hondll NS7&O dirt nck., wa tested by Probably the widest awlngarm In the the II!S7&O milk.. the com • buaI,...