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/126249
Clockwise from left: The nearly complete RMod w ith Works Performance air forks , Th orwaldson pipe, swingarm and sprocket bolts an~ American· built very long travel shocks and springs_Metzelers and full·floating rear brake rod are not yet attached. Gil Va illancourt mod ifies the damp- . ing rods to improve RM forking . , , And is obviously as pleased at the results as we were riding it. Update elderly RMs to latest .specs; make fast and trick faster and tricker By John Huetter Suzuki's RM series motocrossers have been a bombshell dropped right-into the thick of the off-road racingbattles. There's no doubt about that. They have deservedly gained the reputa- 16 tion as the finest stock 250 and 500 class motocross bikes .ever released from Japan . It --:as predicted that th ey would be flooding tracks across the cou n.t ~ with a se~ of yellow, and the predictions were right. The question now in some .racers minds. though , is how to make th eir RM that slight b it more competi tive or com fort a ble to ride than th e do zens of other RMs com peting against them . There's more to it than that , of course . Most Europeans; and Japanese riders for that matter , race whatever th e factory builds. Modification might ext end to changing handlebar grips. Americans seem hell -bent for leather . . . h" h on cusw m lzmg everyt mg t ey own ddi h I h h '11 a mg t at persona tou c t a t WI iff rna k e t hei bik e a li Ie d 1 e re n t or err 1 Itt be tter than th e othe r g uy's. Fr om a practical sta nd poi nt , a lso, Suzu ki has co me so close to producing a fu llfledged, ou t-of-the-cr a te G ra nd Prix bi ke that t he tempta tio n is st rong to go th ose few ste ps further a nd re~n e it, . into somet hing close to the ulti m at e t rick Orient al ra cer. ' W e dealt wit h tha t temptation lik e we deal with most temptations - ~ave in to it. There were some t hi ngl> th at we re less than 'perfect abou ~ th.e sta nd ard RM.s , thm.gs t~ at . d ld n. t b e c o~ e o bvio us until you d lived wit h th c bik e for a .while. First off, th e rnld -st rok e dampmg of the fr ont forks co u ld sta nd improvemen t. T ha t 8 .5 inc hes of travel got very bu sy a nd som ewh at con fus~d wh en braking . into co rners _ ove r s t ~ tl e rb u m ps , a nd wh e!! acce le ra ti ng o u t of co rne rs . G li Va illa ncourt at Wo rks Perfo rma nce h S I ' f k fi ' h i d as a :> or IX t at las proven W 0 h . b I k lik hi t e JO . t war S ixe t IS: I . Rem ove the damping rods fro m the fo rks. 2 ) C lose u p two of the fo u r d amping holes with welding rod . .. 3) File the welds flush and round so the rod is smoot h ag ain . ' 4) Reassemble th e fork slide r . (You' ll need to put the fork ca p on a nd the spring in to get a purchase for tightening th e a lle n scre ws in th e bottom : Ri ch Thorwa ldson also makes a specia l tool that does this .) 5) Put the wheel ba ck on . being careful to lin e up the axl e bush ing and fork leg slot s. 6) Remove th e springs and com plete ly compress the forks as fa r d own as they'll go. 7) Works Performance fills th e fo rks with Bel Ra y L T -200 flu id to exactl y three in ch es fro m the top . If you ca n' t get or can't a fford BelRay L T ·200 , Gil says that l Ovwt , fo rk flu id o r AT F works well. 8) Cl ean and d ry everythi ng with la cq uer thin ner or solvent. T he caps and threads must not be oily. 9) Use red Loc-tite on the air fo rk ca ps (T he re a re a co u pie of pro · priet a ry brands that fit RM fo rks. - W e used Goki .) wh en insta lling th em fo r m aximum rel iability. This m eans th e fo rks m ust be heat ed to rem ove th e caps bu t th ey won't lea k un der the 35 0 psi of presst!re genera ted by air fo rks under co m pression . The resu lt is inc redi blv fine actio n fro m ai r- fo rks that reall y haven 't leak ed a month lat er. T he fro nt end was t r an sform ed 'fr o m slig ht a nnoya nce ' 'int o pu re pleas ur e a t a ll speed s. The ' g rea tes t visua l d iff e rcn ce between th e RM s a nd th e R N work s Suzu kis is the swinga rm . It is tu h ul ar wit h o ne reinforcin g br a ce on the RM and of fully enc losed box sec tion construction on th e R N . T he fo rmcr is chro me-moly steel ; th e la tt er IS an After all the othe r handling vari· abies we could think of were well sorted out, we tried this basket of .goodies to hold up the rear end two at a time. al umi n um ' monocoqu e unit. W e surmised tha t after four years on U .S, Team Suzuki , R ich T horwaldson would know someth ing about the handling of th e yello w racers . He did and had already developed , after a lot' of tri al . test , and erro r , a n aluminum swinga rm for the RM seri es 250 and 370 . Ri ch bolts it up with th e needle b e arings found in th e sta n da rd swin garm and some a lum in um axle . spacers that have the sa me ou ter di ameter as th e inner butt' o n th e chain adjusting pla tes. T hey also keep the long S uz u ki rear axle from bend ing or flex ing : a p ro b le m encou ntered by so me se rio us rid ers . A no t he r problem encountere d o n th e RM has been the elongation and even tual shearing of th e rear sp roc ket bol t s . . T horwa ldso n h ad se ts ' of sta in less steel sprocket bo lts m ade up W re p lace th e -sta n da rd item s wh ich wer e just too soft. T he wh ole swing a rm a nd re a r sp rocke t o peratio n wok ' a bou t 30 minutes. T he swinga rm mod m ay be th e single best expe nd itu re of m oney on a n RM if you' re a sem iserious ra cer . The a lum in u m arm is much more rigid , m akes the rear end feel more co nt ro lla ble a nd gives very posi tiv e fee d bac k to th e rid er . espec ia lly a t high speed wh er e the sta ndard swinga rm m ay be flexing . W e d id n't reall y feel the pot ent :\ 72 cc e ngi ne n ee d e d a ny i m p ro ve m e nt s hut Th or had de veloped a n expa nsio n cham ber that w ok away some of the RM 's brut al low end power a nd m oved it to the wp