Cycle News - Archive Issues - 1970's

Can-Am 250 MX-I ~ 00 .... u ...0 o ..... u American N.ational MX Champion, or, 31 horses all in the same place need a quick throttle. o Up o n the tan k an d work ing t o k eep the f ro n t end p ut was n ecessa ry w ith the Yokoha ma fr ont t ire. Metzelers. Baru ms or T relleborgs shou ld help. By John Huetter For th e first timein the history of the world, a motorcycle built in North America has won a North 'Am erican Motocross Championship. The year is 1974 an d th e motorcycle is a Can-Am 250 MX-l. Gary Jones mad e his third switch of fact ory rides in as many 6 seasons and won the 250cc clas s o f the Unit ed States National Motocross Championship aga in . He did it on a motorcycle bull t and designed in Canada. If that makes al l American chauvinists and industrial patriots feel bad, it should. The motorcycles , in 125, 175, and 250 displacements may not be unqualified su ccesses but a Can-Am 17 5 under Billy UbI did win the United States T w o -Day Trial Championship an d a Can-Am 250 under Gal)' J ones , with much sup port from Papa Don and brother Dewayne- did win th e Uni ted S t ates 25 0 Mo tocross Ch ampionsh ip . No U.S .·built m achine ex ists t ha t could d o eithe r. T he Canadian s at least had the entrepreneurial courage to try, I so me ti mes get the fee ling ' tha t . as ide fro m the co nsid era ble R&D effo rt in 'th is co untry, th at th e " A m " in Can-Am is a nice gesture to the potentially large A me ri c a n m arket : in this case, co n su m ers and not producers of c h a m p io nsh ip -c a l ib e r moto cro ss equipment. And y et , thinking on how to talk abou t th e Can-Am sensibly, I'm reminded of a " National Lampoon" pa rody wherein the punctuation mark used to personify ' Canada w as th e semi-colon. You know, one of these ; The implied "and" or "but" fit s th e 250 Can-Am mo tocrosser in it s production form. It's good but : . . Strip the machine down to its motive so u rce and you find a big, black Rotax ro t ary valve en gine. Now for so me re as on, probably excellent e ngi neering, Aus tria seems a b le to harbor three o r more factories that produce engin es th a t prod uce large a moun ts of po wer tha t ma ke machine s power ed b y th ese engines go very q u ickly over mo st a ny kind of terrain. KTM won a 2 50 World • Motocross Championship this year in addition to making the 250 Penton one of the most sough t-after m achines in the U.S. m arket. Just down the road from Mattingho fen , wh ere th e KTM en ginee rs do their gas dynamics th ing , the Pu ch fac tory sprawls a midst a plethora of mopeds making engines that gave them th e fastest 380 in Europe (th ou gh not the b est-h andling) an d a third in the 250 World Championship. On e or the oth er o f these Aus trian -b uilt units is probably the fastest 250 piston p ort en gine in the world. And then t he re 's Rotax, a traditional builder of snowmobile engines and constant developer of rotary valve two-stroke technology with m aybe the fastest rotary valve 250 engine. Now we should all be a little embarrassed to realize that sn o wm o b ile engines are more powerful, more reliable a nd last lon ge r wit h less maintenance than c o m pa r a b l e . tw o -stro ke motorcycl e engines. But they are ... a nd do. The rotary valve itself in the 250 Can -Am is mi nimal wh ich gives it lots of horses at lots of RPM. Whether or not this he lps the machine we'll get into in a min u t e . The ports are relatively co m p lex in shape a n d definitely lo o k co m p u t er- d esign ed . When you find out that Rotax is p art o f Dr. Gordon Blai r's research gr oup at Queen's Un iversity, Belfast, it's no bi g surprise. If you tell Blair 's IC L co m p u te r th e truth about wh at yo u w an t fro m an e ngine, it w ill te ll yo u n o lies abo ut t he n ecessary po rt design. Achieving that design an d ma kin g t he e ng ine last is so methi ng for the Ro ta x engineers to sort out. Assu m ing tha t Web co 's Sch enk d yno . also is 'a trut hsaye r, we th en dis co ver th at the Can -A m 250 engine nudges in t o th e previ ousl y u n seal ed 31 h orsepower ra nge, albei t at very hi gh RPM . No w be pa tie nt, we're really ge tting to t he semi-colon pa rt of the Can-Am's pe rso nality. Like, h o w o fte n a re yo u, Mr. Sports ma n Mo to cr o sser , goi ng to b e operati ng yo u r bike at th ose h igh RPM whe n raci n g? On t he other han d , th e m ac hin e seems b uil t to las t for operation at many revs for a reaso nab ly long time. Incl uding the engine, Can-Am d idn't skimp on the components that make up the basic structure of their. 250 motoc rosser. .The design a nd location of the Filtron air cleaner which lead s to a very large volume still ai r chambe r see ms intended to p rolong engine life by keeping extraneous par ticles o u t of it. The m o to r is fired b y a Bosch p o in tless elec tronic igni tion an d carb u reted through a 3 2mm Bing, as are al l Can -Am models with varying je tting . Engine lubri cation is by o il 'inj ec t io n with str ai gh t, undilu t ed 3 0 we ight pressure-fed t o the ma in bearings from the o il res erv oir in th e frame backbone. The !:as-a ir mixture arr ives a t the rotary valve down a fairly long tuned-length intake tract from the ca rb located behind the engine as per piston port pr actice, keep in g en gine width down to about 10 inches. All internal bearings are caged n eedle bearings ; no bushings are used inside the motor. Teflon seals are used a t wha t seem to be logical places to com p ens a te fo r different co e ffic ien ts o f metal expansion. Then you get to that part of motorcycle de sign that is cur ren tly undergoing the closest a tten ti on: frame and suspension. The Can-Am frame is well though t o u t , It is rigid, inheren tly stable but made o f mild st eel against t he current trend to ward chro m e-m o ly stee l frames . The re ar engine m ounting bolt is als o the sw ingarm pi vot bolt which results in con stan t chai n geometry. This means virtually constan t ch ai n . tension (h ence, longer life ) and corresp o ndi ngly less wear on sprockets and gears when bounci n g o ve r the co u n t ry sid e. The steering he ad ra ke can be varied by half-degree in cr ements from 28 degrees out to 32 degree s. Our test bike was set up with th e eccen tric s and washers giving 2 8.5 d egrees of ra ke, intended for t i gh t mo to cro s s c o u r s es and , incidentally, abou t a degree less than the standard rake ' of most cu rr e nt motocross machinery. Up front there a re six inch travel Betor forks, wh ich are rapidly setting the p erformance st andard for what produ c t io n front suspension should be . They are progressive, im part exce lle nt feel , and d o n 't kick bac k even when severely bottomed. The on ly t ime t hey bottomed was when se lecting a bad line res u lted in hitting a potho le in the h ard So"cal adobe after a jump. T he bike con ti nued straight and the rider survived. It is by now axiomati c with the new seals in stalled a t the factory but we'll sa y it a ny way: the Be tors 'n ever leaked a dr op d espite a lot of hard pounding. . The 250 Can -Am comes with S&W

• Cover