Cycle News - Archive Issues - 1990's

·'~a~:£~~;~~>: ;':: r:: ·:·: ?s~i1~I~rt:.:.·: : :. i'~ :~ ~.'~<' : ~i.ili :\:::,~c#' + > . .... •. i- . . .... i. ... ..:.-:.:. .." ::: . . • ' ". .::.: :. : .: ::' .' ': .' , Engine type . : ".; .:. . .:. : ..:~. :' ;" 1m Ha~ey;Davidson v·twin two-yaJve,.pusl)rod·fqur·stroke· . . . : ' . . : . • :. . ' . . . Bore XStroke'·: . ' . ' . , ~ . . .2.983" 3.1 25" m.x.. ..• J!l .• Compression ratio , :. : :., 12.5:1' · . . . ' . :.::.'.:::.:.>~ ,,: ' .: . .' .. . :.:- . ::: :: Knight singie-shock, C1irQllioly fubing . .. -:. . " . ". ' .. '. · ChaSsis .•. '.: : .'. : . '; '. , .', : : ~~ ~ ::~.: ~.:>-:.::;:.::-: ~m~: · .:<..' .: : Wheelbase : ••.,., ., .... . ;; ; . . t; ,,' 54.5 ·.56 in:." - '.: - ': ''". -:' " ; , , . . ' -: -" . : " . ~~'::~:: :> ::-:.;>;:;':~~{J;l:5 ~n: .. ':.':'.... .:::<.::..:....:... '.:. -: : . :. ':..,::. 3.50 x 19<:05Goodyear. ' ., . . ' ' . ' . Reartire ".,..... .; , .:'/ ~ .:', :::;. 4.00x 19 COB GciodyBar . • .... " '. . '. . ,. . . .: .. : · Front fork , ••'; . " : . " : ." ;": . ; '; ', WMe POW~tu~wncartridge lork, tunedbyWMeBros: Rear'shock :';,-.:: :' »: » : .~;;' :, .: " :'-:(1) WMe poWersilock, tunildby Wl\~· BroS . .. . ' . '.. , Frontlire ." . =t== ::.: ·:·; ( ::: :.,: .: .: ~:.~ ~:,: ·Re!lr b~ke : ',",.":,::,, ,:::':::"::::':: ::.':,", .:::.. .'..... .'.. . : , . •. :' '. ; . .,: .: ': : : '.': Perfo~11C8 ~i~ ca!!per, KOS~' ~isc , ; .. : . ; ~O Oiing Tsubaki " ' : . ' : ·Claimed dry weight,: . , " . .:-. : . :-.320.Ibs. . . . :. . ' '. . ',.,' . . .' . . . . ." . ' ;" .. . . .: . . . . . . ' . . '. : . .. .. ' .' ., . ". . . . ;. Analdrive ' A total of 40 Hon daRS7 50eng ines wereproduced byAmerican Honda in 1983, and2B of them weresold through 1990. The rem aining12 wereused bythe factoryfortheir raoe team, which contested the Grand National Championship Series from 1983 through 1987. The four·valve, overhead cam engine is known forproducinga high·revving, hard-hitting type of power - one that is bes1 suited formile tracks. Incomparison to a Harley·Davidson XR750 engine, the RS750 produoes most of its power in the higher end of the RPM range, while the Harley makes itspower down low. "I'vefouOd that the Honda engine is more dependable: saysJohnny Goad, owner ofthe Hondas that Ricky Grahampiloted tothe 1993 Grand Na tional Cha · mpi onship. "Power·wise, they're really prettyclose, butthe Honda has a different powerband. My Hondas will tum 11 thousand RPM, whereas a Harley will probably tum 9600.· According to Goad, parts forthe Honda engine are easilyattained, but their prices are noticeably higher than parts fora Harley. "Yeah, the parts are prettyexpensive, butthey lasta lotlonger. Acrank costs $3800, but ~ win last three years. Also, you can bolt Honda parts right on.You can slap a set of pistons right in, but you have to spend a lot of time machiningHarley pistons before you can install them." Asforthe rest of the motorcycle, Goad reports that minor suspension and gearing changes are all that hemakes from track to track. Until this season, Honda riders were the only raoers onthe track with single-shocked rear suspension. "The single-shocked rear endis a little tricky to get figured out atfirst,· says Goad. "Butonoe you understand it,you can make ~ work really good." F ... 1 26 ~ ... ~ . ' .~ . irst introduced in 1972, the aluminum XR750 engine has undergone only mino changes in the last 22 r years. According to Team Harley-Davidson tuner Kenny Tolbert, the latest version was introduced in 1990. "They came out w~ bigger flywheel joumaJs and bigger main bearings: sa ysTolbert."But other than mat, the motor isbasically the same asthe firstaluminum XA. ·Right now, we're getting around 100 horsepower out of ourengines, but I don1 think thatthey're tapped out ye~· sa ysTo rt.·A few years ago we weregetting 95or96 and thou that was ~, but thenwe got lbe ght -B 100,1don't see 105asbeing that unrealistic. The push rod, two-valve engine is justthe same asa dam V Chevy, but I think it's a well-proven de n." sig TDIbert reports that hespend upto 14ho ursa day working on the engines that cany Chris Carr aroundthe Nation's ovals. 'Someone asked me once how many hours ~ took tobu ildanXR eng and I said, 'Asmany asyou can ge 'l ine, l tear the engine apart after every raoe tocheck everything. I check the crank every two races, and I 'd say that pistons last about four races." And speaking ofpistons, Tolbe admits that rt he spends at least three hours machining each se of pistons before they can be installed. "It t takesa lot ofguys about six hours, butI'vedone somany that I have ~ down to a scienoe: he said. "It seemslike you'renever done working on a raoe bike. There's justsoGod awful much work.· 0\ C'I Q) ~ III

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