Cycle News - Archive Issues - 1980's

o . •• . , . . . o. ..... ~.,. - ....... ..... The end result: a KTM engine type 565 reduced to a mass of parts . The only major components lef t int act are the crankshaft and gear shafts . At 218 pounds dry. the water-cooled 500MX is the lightest production 500cc motocrosser available in 1985. radia tor s but includin g th e ca rbureto r. kickstarr er a nd sh ifter) tip s th e sca les at 58.4 pounds - I i .6 p ounds less th an th e 495 model - tha n ks to weigh I'cu u in g mea su res throughout t he engine. KTM ha s co n tinned to shrin k t h e ca ses with eac h new engine ge ne ra. lio n, and the 500 has ta ken the pra r- tice to new heights. Th e case s arc ever so co m pa ct a nd hold a meager 500cc of o il (l h<'495 mod el had a ca pacity of 1400cc); there is vir tu al ly no wasted sp ace insi de th is eng ine . T he weigh t savi ng th em e com in ues o n rh« o u ts ide o f t h e eng ine as we ll. T he fol d ing sh ift lever is cas t al u min u m ; the igni tion cover is plast ic: a nd th e ca r bureto r is a 40m m Bin g wi th a ma gnes iu m bod y (w h ich is I igh ter th an I he customa ry a lu m in um ) a nd a pl ast ir floa t bo w l. T he fu ll y wa ter-j aek en-d cy linde r and head are sa nd cas l a lumi n um and have th e ro ug h " works" appeara nn'. T he cen ter cases are d ie-cast aluminum with a smooth exterior fini sh. KTM could 've sa ved a few more o u n ces here had th ey staye d with the magn esium used o n th e 495. but as it sta n ds th e a lu mi n u m cases o n th e 500 still weigh less due to th eir sma ller proportions. The onl y m ajor ma gnesium p an is th e die-cas t clutch cover , whi ch is fin ished with an a lu m i n u m paint 10 a p p ro x im ate th e color o f th e rest of th e en gi ne. Th e 495 had a n alu m inum clutch cover. The finless cyli nder as well as th e head have an unusual octagonal cross section, a nd their relat ivel y co m pact dimensions belie th e size of th e for ged a lu m in u m p iston wh ich live s in side. The 500 (act ua ll y 485cc).has a slig h rlv smaller 89mm bore and longer i 8mm stro ke than th e 495 , which m easured 92.5mm x i4mm . T he 500 piston ha s a n o va l-sha ped inta ke pan nearl y ide ntical 10 th a t of th e 495, but th e 500 has a full-l ength skin o n th e inta ke side wh il e th e 495 was partiall y cut a way . Eith er p isIon would make a rea sonabl e co ffee mug with th e addition of a handle due 10 th eir nearl y-four-inch d iameters. KTM has gone 10 a N ikasil bo re in th e 500 in lieu of th e hea vv steel lin er o f th e 495. Nika sil . a co m bi na lio n of n ick el and si licone ca r bide, is a p p lied d irectly to th e a lu mi n u m wall s of th e cylinde r by a n electro pl ating process, a nd th e result is a mu ch lighter cylinder. Th e cy li n de rs are cas t at KTM 's manufacturing p lant in Maui gholen. Au stria, the n sh ip pe d to major Euro'pea n engine co m po ne nt ma n u lacturer , Mahl e, in Stuu gart. West G er man y. w here th ey a n, elertroroa red wit h N ikasi l th en di a mond ho n ed . Mahl e a lso supplies th e p istons. Accordi ng to KT;\[ engi neers , t he N ikasil bo re offers a more eve n hea t Ira ns fer ra re tha n ei ther steel or chrome bores. And since n ickel is more rous than chro e

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