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/126831
lr) 00 O"l ...... The very small and narrow engine cases make for a slim profile. The sand -cast aluminum cylinder has an electroplated Nikasil bore . A totally new design for 1985, the engine in the KTM 500MX is extremely compact and lightweight for its size. Engine teartlown: KTM 500MX Beneath the skin of the Austrian half-liter By Tom Kolnowski We've often w o n d ered j u s t ho w m an y motocross/off-road riders use - really use - every morsel of power available in their 500cc mills. We know motocrossers David Bail ey a n d Broe Glov er must co me very cl ose; en d u ro pilots T erry Cunni ngham a n d Kevi n Hines wo u ld be ri ght in th ere, 22 -, I ~ .\ too; a nd certai nly, dese rt racers Dan Sm i th a n d Dan Ash craft wou ld be likely ca ndida tes. And su rp risingly. it's not uncom mon fo r o ne of these ri ders to as k C r more - mo re torque, o more horsepower, mo re speed, mo re everyt h ing. Stra nge ly enough, development engi nee rs go back to th eir dra win g boards a n d co me back with more and less. Wh ile at th e sa me ti me increas ing torque, useable power, etr.. the result in g power pla n t is o fte n li gh ter in weight. sli mmer a n d trim m er than. its predecessor. T his is "I I ) i I . r 1. ' 1 *) _ J I i I . 1 ( 1 ) 1 ~ h t . r-. tr ue n ot o n ly in th e exo tic " wo rks" mot ors, but a lso in th e sa me engines in th e bikes we bu y ri ght ocrthe showroom floor. Suc h is the case with th e liqu id -cooled mo tor in the 1985 KT M 500M X an d MX C models, a to ta lly new p ower pl an t Irorn the Au stria n manufacturer wh ich is a repl acem ent Cor th e air-cooled engi ne which graced th eir 495 model s o f th e p ast C years. ew P rio r to 1985, th ere we re n o 500cc wat er- coo led mot ocross o r o ff-roa d bikes o n the market (t he largest watercooled d irt bike a va ila ble before '85 wa s th e '84 Hu sk y 400 WR end u ro) . KTM has neith er wo n n or lost th e batt le to bring th e first fu ll 500cc liqu id- co ol er to the mar ket p lace: H onda , Husk y. Ka wa sak i a nd MSta r a lso ha ve '85 models of th at de - scri ption. Th e KTM 500MX does have on e clai m to Ca me, h ow ever: i t has th e lo west d ry weight oC the bu n ch a t 218.3 pounds. Next co me s th e Kawa sa ki KX500 (220.5), th en th e H onda C R 500R (223.8), the Husky 500CR (224) a nd th e M-Star GM500 (233). T han ks to a severe weight reduction . program in the eng ine depa rt ment, th e total 500MX p ackage weighs nearl y 17 po unds less th an th e 495MX it repl aced. What mak es this new wave of engi nes tick ? Wh a t bett er way to find ou t tha n to do a co m p lete engi ne teardown, an d si nce we had a KTM a t o ur d isposa l, th e motor ca me o u t o f th e frame and went "u nder the wren ch ." - Th e man beh ind th e wren ch es was Bar ry Higgin s of H&H KT M in Mab leto n, Georgia - a nd th e engine we used C dissection was C from Iacor ar to ry fresh . T he m ill had already spent nearly 2000 m il es in th e hands o f H iggin s under mot ocro ss, en duro and hare scra mbles co ndi tions. Wh ile we d isassem bled th e engi ne from a 500MX, every th ing we' ll say a lso goes Cor the 500MXC (end uro) ; ))) 11 1 ' 1 1 ( i i r, - r : 1 1 11 Octagonal in shape, the cylinder head is fully water-jacketed. versio n since th e two motors are iden tical, part fo r part. The only difference is the addi tion of a lighting co il to th e ignit ion system o n th e MXC. As we lifted th e engine o u t o f th e fra me a n d o n to th e work be nc h, the C irstthin gs we noti ced were th e ligh t we ig h t a nd extreme o vera ll co m pactness. Amazi ngly, th e 500 engine (sa ns - );' ( ยท.I , , )l: .. ,lc 'I t .1 . t l l , I ) J