Cycle News - Archive Issues - 1980's

The 500 piston (left) has 'a fu ll- length skirt, while the unit from the '84 495MX (rig ht ) has a cutaway skirt. The crank has full -circle flywheels, while the forged con necting rod is se'ated in needle bearings. 24 - While most 500s have four-speed transmissions. KTM has e lected to stay with a beefy five-speed unit. Cool water enters the clutch cover spigot (top) and is forced through .the engine by an impeller (bottom). bore a lso has be u er oi l ret ention bikes w ith a n eig h t-bolt cylin de r head .(six is a verage), a nd th e cap scre ws a re p roperties. The silicone carbide is made from h igh-ten sile-str en g th steel. app lied in specks to reduce th e wea r Even more unusu a l is the head gasket, factor. Like a ch ro me cy li n der, Nik asil wh ich is ver y thin a nd made from white paper. And the gas ket, which is ca n' t be bored . The Ni kasil bore, ho wever, ca n be resurface d by Ma hl e less than \4 in ch wid e, is located a t th e very perimeter o f the ma ting surface ; in German y - a less cost ly a lterna tive to buy ing a new cylinder. To reduce the rest of th e cy li n der / head co ntact th e turnaro u n d time for V .S. rider s, a rea is meta l-to-metal with a super Ma h le is ex pected to o pe n a resu rfac smooth su rface fin ish. Most wa ter coo led tw o-strokes make use o f ei the r ing faci li ty in the New Engla nd a rea . Honi ng to a llevia te minor cylinde r an O-ring or co n ventio nal gasket bet ween th e wa ter jacket a nd bore. damage is a lso o ut o f the questio n , KT M e ngines a lso depart from the si nce th e po res in th e n ickel su rface norm in th e base gas ket department. tend to re tai n de bris (s uch as sa nd) The deck h eight - th e di stance from a nd th e h one wi ll o n ly expose more th e top of th e pist on (meas ured a t th e of th e silico n e ca r bide specks perim eter of th e piston a t top dead i n crea s'ing t he wear fa ctor. KTM center ) to th e " deck" (the to p of th e reco mmends im mersi ng th e cylinder cylinder wa ll ) - m ust be in th e ra nge in a n ult raso n ic ta n k. wh ich will o f 0.9 to l.l mm . To a llo w fo r m inute unclog the pores a nd make t he cylinder servicea ble o nce aga in . U ltrason ic d iffe re nc es in cylinders, gas ke ts a nd p isto ns , th e base gas kets for th e 500 cle an er s a rc fill ed wi th a specia l flu id come in thicknesses o f 0.2,0.3 a n d a nd utilize sound wav es; jew eler s O.4m m. co m mon ly use them for clean ing The deck heig h t is m easured wi th di a mond rings, etc, On the intake side of th e cy l in d er is th e gaske t in p lace a nd a fte r the four a ca st-i n , sligh tly-ang led reed blo c k bo l ts o n th e base of th e cylinder ha ve been ti gh ten ed (the best too l for wh ich is probably rnorevcavern ous mea suring is a vern ier ca lipe r wi th thau that o f a ny o the r d in bi ke. I t an integra l depth ga uge). If th e mea houses a n eq ua lly-m assi ve e ig h t-pe ta l surem ent isn' t up to specs, th e gaske t reed va lve system (wit h s in gl e-stage has to be cha nged to bri ng th ings in fi berg la ss pe ta ls). T he passageway line. o pe ns to th e cy linde r via a br id ged T he cylinder a nd h ead have eig h t intake p or t a n d a pa ir of sm a ll boost ma in vert ical water passageways, a nd po n s wh ich origi na te in the ceiling th e three wh ich serve the ex ha ust o f t he reed bl ock. T he rest of th e port ing is q uite conventiona l; six tra nsfers p ort area a re br id ged as th ey open into the head. T he 1.5 quart of coola nt a nd a la rge center ex ha us t port . T ile' KTM 'i~ '0 e-al"a very few din ' • • t 2 ~ t ':Jn ri ~ f te-e1: e 1 ""'aTe r - rrti"xl'lJrt: , - is circu la ted through th e sys tem by a ver y sim p le plasti c impell er , wh ich is driven off th e left end of th e cranksha ft (a n d a lwa ys turns the same d irect ion as the rea r whe el ). T he cooles t water (w h ic h flow s o ut o f the bottom o f th e left radiator) is routed into th e cl u tch co ver a nd to th e im pe lle r. As it spins, the impeller pumps w e wa te r through a hose to th e hottest a rea first - the exhaust port. From there, th e wat er flo ws up through the cylinder, pa sses th ro ugh the head , then is rou ted ou t the spo u t at the top. At it s h ig h est tem pera tu re as it exits th e head, the water is th en pumped back to th e radi a tors to repeat . th e cycle. T he crankshaft itse lf fo ll o ws curren t pract ice for a 500cc two-stroke sin gl e wit h full -circle flywheels, and ha s th e customary roller bearings at each e nd . The bea rin g locators, howeve r, are low-friction plastic instead of the usu a l bronze . T he locators in o ur mo to r showed no signs of br eaking down even after 2000 mi les. T h e ignition system, a basic CO L unit, comes fro m Mo to p lat a nd resid es o n the left en d of the cra n ksha ft. The ign ition coil is m ou nted to the fram e. . O pera ted by an ex terna l lever loca ted j ust ahead of the co un ters ha ft sprocket, th e cl u tc h has n ine si ntered bronze fr iction pla tes rather than th e more common fiber pla tes. T he bas ket is ca st a luminum a nd r ides in needl e bea rings. The tren d in 500cc motors of late ha s been to go to a four-speed tra n sm ission , bu t all KT M 500s sh ip ped to th e V .S. ha ve five speeds. A fo urspeed version is a va ila ble in Eu rope. how ever. Bot h versions share the same rela tively sho n shafts and beefy gears, a nd the resu lt is still a very co m pact cl uster. The Europea n version has a spacer in p lace of first gear o n th e driver shaft. The sh ifti ng mechan ism , three shifting forks a nd drum h ol d n o surprises, bu t th e KTM does ha ve a n ex tre mely shan sh ifter shaft (approxima tel y th ree in ches). Si nce th e coun tersh aft exi ts th e eng ine on th e righ t (j us t th e opposi te of th e Japanese way of doin g things), th e sh ifting mech an ism is nestled in to th e left side o f th e cases an d KTM ca n ge l a wa y with a lighter , a bbrevia ted sha ft. By relocating th e kickstarter asse mbly to th e top o f th e cases o n th e left side (i ns tea d o f o n th e bottom left as o n th e 495), KTM was a ble to slim do wn the cases eve n more whi le a t th e sa me time sav ing weight. They o p ted fo r a h ea vy for ged s tee l ki ckstarter ins tea d of th e lighter alum inum uni ts which arc fi lter ing in to th e m arket . a nd co nsi de ri ng th e health y kick requ ir ed to sta n th e mot o r, it was probab ly a wise choice. So th ere yo u have it: the KTM 500MX eng ine ex posed. Ov erall . we were im pressed with th e ease in which the mo to r ca me a part , and how eas ily it went back togeth er - a ll witho ut th e need for S1000 in special engine tools . The p eople at KTM should be proud of th eir crea tio n: th ey've proven simpli cit y still h as a place a mon g sta te-of-the -a n d esign, hi g h tech n o lo gy a nd th e race for less wei ght. • Specifications Clutch cover Eng ine model KTM type 565 Engine type Water-cooled. reed -valve. two-stroke single Bore x stroke S9 \x 7Smm Displacement 495cc 'C arburetion . . 40mm magnesium Bing Ignition . .. . External rotor Motoplat COl Lubrication . . • . . . . . 40:1 to 50:1 pre-mix Gear rati os Primary 2 .62 Final . . . . . ... . • . .. . . . .. . . . . 3 .71 0.74 5 th 4 th 0 .95 3rd 1. 1 7 2 nd 1 .5 0 1 st 2 .50 Cylinder • . Sand-cast aluminum. Nikasil bore Cyli nder head .. . . • .. . Sand -cast al umin um Cran kcases . • . Die -cast aluminum magnesium Ignition cover Plastic Crankshaft . . Full-circle f lywheels. roller bea ring -supported Connect ing rod . . . . • Forged steel needle bearings on both ends Piston . . .' Mahle forged aluminum. dual ri ng Water pump .. . .. Plastic i m pell er Clutch •. .. . We t . sintered bronze friction plates Reed va lve . .. . Eight-petal f iberglass. single-stage Kicksta rter Forged steel Shi f ter Forged aluminum. f ol di ng Ig nition ti m in g . .. . 2 .1 - 2 .2mm BTDC Deck height 0 .9 - 1 .1 mm Oil capacity 500cc. SAE SOW/90 Coolant. , . • • 1 .5 qts.. 2 :1 antlfreeze /water m ix Eng ine dry weight . .... 67.6 Ibs . -Dle -e as t

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