Cycle News - Archive Issues - 1980's

FZ7S0 The new Yoshlmurcll PRO-Ser1es SYStem for trte HI"i' Is a true fOur Into one system that tudeS Into me nOde falrtng fOr Exhaust ~ . . . . street --- Ugnt wetght and pertormailce wtIlte retaining centerstand, 011 filter ;md 011 drain maximum cornering Clearance. access. $250. stili provides fOr centerstand retentton, ancl ts S1gnfflcanttv IIgnter tnan stock or otner artermmet fOur Into two svstems. All PRO-Serles EXhaust sYStems feature our IlQhtweiQht ~ Our aluminum Cilnlster Silencers that replace stOCk mufflers fOr 1m. Drovect kIOkS wnlle reduclno aluminum c:antster $Uencer sup. $1•. =~~~U~O::~I" ferent deSIgnS: fOr most mOdelS of Honda. Yamaha. SUZUki Jnd KHaSakI In ettner ICaI-Gard flnl$l'l or ol'ttONll Blade cnrome.. PlIO Ie ... 1OIId bc8 DesIQneCI wIthOut COFnp, omlse tor maxtmum pawer and comer· trig dennal on street or mtet. center'Stand removal USUiIY ,. qulr'lCt. $250. COmP'ete RoadRK'e svstems for Honda VF SOD. 750. 1CXX1 tntercepten $271. -.ons wetarlt and uncor1clng TIM! YOIhmurll.Jlcttt •••.•..••.•••.•• pOWeI'1 ORDER TOLL FREEl (800)634-9166 InCA1714162B-4722 , .. f'rOm S 4UD frOm S,. . . db sa" Tun YosI*nln tw: ...•_.•......•..•. S 5.00 YOIIllmUr1 JudllY IlIg w/bUngles • _• • •M fUii== ~ PIItlWl The FZ750's gas tank is behind the cylinder head. and the center of gravity moves downward rather than rearward as fuel is used. 'tOShImlll'llhclng/COll'lYT.stlIrt••••.••• $ ••" T."YosIlIrrlInHtllrtltedorWlltl, .. S 7,SO YosIllmUrll StreIt JICUt: " .. . . " '.......... Nrts ==:.C:Udts:":':= r::: .-v DlIlV CJrll 0lIInI =,OI=-.~W~~·s·=$1IUD ==~=.:':: ...., U'l' FOrtlSDrtn05 •••••• S _ = = ...., DlIlV 5InlIIt Wldl-.no s - =: =::=: . . 1liIIlln CI SOIdIl ~ DI'MlIOllNn CI SDIdIl CII'tII: -.n Irlll WIodlY __ _-,",=,==:':il $8500· THE most expensive. trickest .shirt in the world. Be the only one on your block. or in your state. for that matter; to own this ultimate shirt. For 19B5, .only ten will be made for the AMERICROSS TOURS racing team. If you join the team. you'll also get: Summer-long travel Nationwide, 65 days of intensive motocross training; ride and race on our team bikes; train on our mountain bikes; full complement of protective gear including boots, gloves. goggles. helmets, leathers; food, lodging, transportation, racquetball, personal video taping, '""--_ _-1. bike prep instruction, career counseling, and much, much more. We even pay you race bonuses. - AMERICROSS TOURS 1985 entries are now open. We have spots on the team for just 10 serious riders. Preentries for four racers have already been received, so don't be left out! Call today for the experience of a lifetime. - (~. 74 ~ AMERICROSS TOURS 1985 P.o. Box 910, Alta Lorna, CA 91701 (714) 980-3212 ENGINE DYNAMICS _ ,'r.llih/.,/"" ~.'~ ~ ~ (707) 763- 7519 - ... au N~H IN E • E.-perl Full Race HEADS CYLINDER t:'\, We slock valvtls. Prep & Damage Repalf tile gUIC:les. springs. cams. : \t , 1010 lakeville Hwy .• Petaluma, CA 949520 _, ~~~ I 1, I''';'' (CuIIIIIIIII'" !mllljlll.li:(' ill ODe., 7 Day. 11·7 W_doy•. 10·6 Sot.• Sun. Motorcvcle larger Aee • • • o;. ••• Selection 18314 8each Blvd.. Huntington Beach. .-(1714184'7-5300 CA ~~o.~ Stores ..... -0 power output was obtained by deLUning the 01 I engine, but there were many difficulties in the process of making a "perfect" product. The distances between carburetors, for example, were shortened by 4mm by the exterior designers because otherwise body width would be excessive. Every possible means was taken to make the ooM engine as narrow as possible, from cam cover to crankcase. The "vertical"' fuel tank, with the airbox below and in from, permitted an ideally-slim tank< rear-section. However, manufacluring it was so difficult that a special stamping machine for the tank alone had to be developed and a new manufacturing procedure introduced. Exhaust gas flow was speeded up by utilizing exhaust pulsations this improves torque around 5000 rpm. After intensive studies assisted by CAD, the four-into-one-into-two exhaust system connecting cylinders one and four and two and three was chosen. The four-into-one exhaust used on the 011 street-version was' discarded due to centerstand interference and for overall sty ling. The engine would be housed in a chassis using a wide-cradle frame, rising-rate Monocross rear suspension and highly rigid front forks - all proven for performance and reliability on the RD500LCand Fj 1100. The frame design, developed originally . for the square'-four YZR500 of· ome years ago, was to be fabricated of boxsection tubes made of high tensile steel. The high-rigidity frame gave excellent cornering performance and high-speed stability. This particular frame, though heavier than aluminum frames, was chosen because Yamaha believes that the chassis (including tires, wheels, front and rear suspension and main frame) should be perfectly balanced to match the engine'~ power, rather than being extremely light and too rigid. (Yes, it is possible for a chassis to be too rigid.) in contrast to the time spent on advanced research and development, the OOM's development was quicker and smoother than expected. The hardest task for the development staff was not talking about the number ot valves with other Yamaha employees not involved in the OOM project. Even Yamaha's overseas imponers were not told of the five-valve head until the official announcement of the OOM. Components discarded after tests were stored in the engineering department. Pistons. for example, show the _e. ••• •••• • number of valves in the head by the recesses in their crowns. Because the capacity of the OOM was also a seaN, the staff responsible for crankcase manufacwring thoughttbe new model would be a 400cc because the cases were 9mm narrower than the air-cooled Xj4oo1 Testing on public roads aftet finishing tests at Yamaha's Fukuroi proving ground was difficult, because the deeply-slanted cylinders were very conspicuous. By mid-1984, many prototypes had been built and improved. The five-valve cylinder head Featuring three intake valves and two exhausts, the FZ750's cy1inder head increases horsepower, mid-range torque and combustion efficiency by increasing intake volume and velocity, and allowing optimal combustion chamber shape. Individual valves can also be made smaller and lighter for quicker lift response - one of the reasons for the FZ750's quick-revving characteristics. Three intake valves give a larger intake volume than two, and more fuel/air mixture flowing through the head means increased horsepower. Since the individual intake tracts are smaller in diameter, intake velocity is increased for excellent mid-range performance and instant throttle response. Because the e smaller intake valves are also lighter (21.1 grams each) reciprocating weight is reduced for a much higher rpm ceiling before valve float sets in. A ingle spring is used to seat both intake and exhaust valves. This reduces valve seat pressure and quickens valve lift while reducing valve and seat wear. Each intake valve stem is "wai ted" te reduce flow obstruction to a minimum and intake guides protrude only slightly into the pons - exhaust guides are smaller in diameter where they protrude into the pons. The net result is low flow, obstruction, very effective cylinder filling and instant response to throttle applications. Mechanical loss and wear and reciprocating weight are futher reduced by operating the valves directly off the hollow camshafts. A Yamaha tradition with twin- am engines, direct valve operation also eliminates side thrusts on the valve stems caused by rocker arms. Interestingly. the total intake valve area is less than with a four-valve configuration. Even the valve lift figure is slightly less because less radical cam working angles can be used. • • ••• •

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