Cycle News - Archive Issues - 1970's

eD on 't sh'o ot th at Po lit ica l Briefs . II: ~36oYamaha ~ M ak ei ta 40 0! O'l By Lane Camp bell By A. H. Tellie r 1:"'~ Red Moun tain/EI Paso Plans released Bigg er is not nece ssari ly bett er whe n it com es "'; to mot orcy cle engi nes; part icula rly two-stro ke ~ singles. Rem emb er the 450 H usky and the 500 g Yam aha? How ever , a larg er engi ne is capa ble The first of m a ny specia lly deta ile d plans for units in the BL M· adm in istere d C a lifo rnia desert was release d during De- O'l Cl$ ~ The spacer sho uld be constru cted of produc ing grea ter torque and , if it o ut of 311 6" th ick alumi nu m plate to produce m ore is well designe d, it will m atch th e base gas ket. Trace th e · horsepo wer than a sim ila r engi ne of ou tli ne of the gas ket on a ny. fla t, cem e n t. O b vio u sly, sma lle r displa 'sm ooth al umi n um alloy pl at e. T his ther e are diminis hing returns, suc h spacer co m pe nsa tes fo r the d ifferenc es 360 barrel o n a 250 th at stu ffing a in co nnecti ng rod len gth be twee n th e crankca se will not give the expected two engi ne design s. T h is ' pl at e is to insufficient cra nkcase · resul ts due sa nd wic he d betw een two 360 cc base a nd transfe r volu mes . But relatively gas ke ts, we ll sea led (Gascac inch , o r in inc reases ( 10· 15%) sm a ll eq uiva len t.) a nd p laced below the displa cement a re well within th e realm barrel. . engine designs . of existing The possibility of replaci ng the old Relati vel y si m p le m e thods ca n rod with t he new , short . unit was a 360 Yam aha single in to a . cha nge exp lore d , but th e piston speed wou ld 400. (T hese are , of co u rse, nom in al be increased wh ich wou ld , in turn, isp laceme nt va lues . Actuall y we a re d reduce the po rt tim e-area values . As 46 cc : 351 dealing with an inc rease of thi s would be observ ed a s a up to 397. ) This in crease of 13% is th e . perform ance degrad ation , the spacer re: 80 mm to result ofa five mm overbo method was chosen a nd the barrel 85 mm . The necessary 118 + " overbo re raised. stru ctu ra l (0 .12 71) is well within the The 400 piston requires the 400 a n d therma l cap abilit ies of the wrist pin , as it is shorter than the 360 -inIron lin er. irregula rly-sha ped, cast pin. ALWA YS install new pin clips. Metho ds will be si m u l t a ne o u sly They are ch eap insuran ce. Similar ly, th e effi cien cy ou tlined . for increasin g this is a good time to re pl ace the upper of the engine. Aft er a ll. wh y not rod be aring. The first -over rings are red package produc e a totally- enginee used due to the co ncern regardin g end e the opportu nity presents itsel f. • whil gap values. Experien ce has shown that 360 cc The engi ne is thetibi quitous the . us e of the " p rope r" size rings reed -va lved , single cy linder, two produces an end ga p which exceeds barrel. This stroke , using th e Enduro th e Yamah a tol erance limits. giv ing barrel is suggested due to the va ri ety of away some compression a nd ring life With the modifie d uses project ed. prior to use. The answer is the use of · Enduro barrel , th e ' power band is th e ne xt la rger size ring with the end th e engine tractab le . very broad and gap cu stom-fi led to the d esired low The parts whi ch must be obtaine d value of the tol erance band: 0 .0 16" for this project a re: (0 .4 mm). Be ce rt ain to all ow space for r a ) 400 cc Yamah a Piston , MX o th e anti-ro tation p in . Dupli cat e Enduro . o r ig ina l ring e n d co n fig u ra t io n : b) 400 cc Yamah a Ripg(s) , First otherw ise assemb ly will be impossibl e . Oversize . The selecti on of either the MX or , c) 400 cc Yamah a Piston pin Enduro piston . depend s upon your . qips(2) . Bearing and perso na l and u se proj ect ed d) 360 cc Yamah a Base Gaske ts(2). mainte nance . hab its . Howeve r , the . (0 .1875) Alumin um Barrel ' e) 3116" . MX piston ha s an abbrev iated ski rt Sp acer Plate. with a large , open ended window , e latter spacer plate are offAll but th reducin g piston stabilit y. The End uro a the-she lf items from any Yamah piston workse qual ly well if th e intake In additio n to th ese hardwa re dealer. skirt is cu t off at the lower, inner must be items, the cylinde r head casting ste p: remove 0.325" . Do not machin ed to the new nomina l 'b ore cut the exh aust sid e . the cylinde r diamet er of 85 m /m ; and Th e cy li n de r h ead mu st be must be bored to the new piston size . mach in ed on eithe r a lathe -o r a rnil l., cylind er was In Phoeni x , th e . relieve th e existing outer squish band machin ed to within ten thousan dths out to 85 mm di amet er. If this is not honed to th e (0 .0 10"), then precisio n done , the deck height will be far too fin al size (0.0025 " clearan ce) at Bill small , with the clearan ce being filled , 3921 W. _T a nk's Precisio n Honing by carbon and combus tion produc ts Clarend on. IEllURR ALL Bikers nomin ated to Deser t Conse rvation Advis ory Comm ittee O n e of many parts of the recently enacted " BLM O rganic Act" was the establis hment of a Califor nia Desert Co nservation Area. Also included in the law was the formati on of a citizens ' advisor y commi ttee. Lett ers went out during Decem ber to all persons who had ever express ed interest in 'desert plannin g, outlinin g the commit tee's charter. asking for comme nts, and asking for membe r nomina tions. The B L M receive d over 100 250 roughl y with respons es - nomina tions. Among those nomina ted were DRA's Ron Bu rpo, AMA D-37 activist s Bob Tamer and Jim Wells, Cycle News Corres ponden t and U.E .A. membe r Larry Langley , Cycle News Editor Lane Campb ell, desert rider/p ark commis sioner Pat Rice , (to represe nt local govern ment) , ' and Univer sity of Califor nia, Sa n ta Ba rbara profess or A.E. Keir Nash (to re present sociolog y). Many of the comme nts focused on the fact that the propose d co m mittee was heavily " st a cked" in lavor of preserv ationist s, and that recreat ion interes ts were u n d e r -r epresen ted . ~ LM Sta te Directo r Ed H astey has pledge din a .follow-up letter that these co ncerns wo uld b e. reflecte d in a . revised commi ttee char ter, ; Sequo ia Nation al Fores t ' ORVP an = MACHINE TO 85 !'\1M DrAHE'mR AF'ml - MACHIN~ 85 18 cember . Many motorc ycle 'clu bs and , groups . notably the Desert R a cin g Assn . (D RA). the United Enduro Assn . (UEA), AMA District 37 and the Nat'I , Outdoo r Coaliti on, made detailed ' present ations to the Bu rea u during the months -long pl anning process . With detaile d study . it's appare nt that the bikers' efforts did have some limited effect on the final form of the plans. I ndividu al riders . clubs and groups should write the BLM and obtain cop ies of the plan with its multi colored plannin g unit maps (they're fre e) . Motorcycle Owners . Riders , and Enthus iasts (M. O . R. E.) Chapte rs, especia lly, should becom e familia r with these .close- in desert regions and to plan group inspect ion rides to areas of interest. Get "the plans by writing to the Bureau of Land Manag ement, 35068 Ba rstow Rd . Barstow , CA 923 1I , until co ntact is m ad e with the p iston , crown. . Similar ly. the co p pe r head gasket in side diamet er must be cu t out to 85 mm. Copper project ing into th e com bustion cha m be r will glow and result in p re ign ition. The cop per is soft and a ha nd file o r ro ta ry grinder will work well . Be ce rtain to d eburr th o; new ID su rfa ce well after it is cu t to size. . With t he new. la rger . bore th e igni tio n timing should be advanc ed in o rder to com pe nsate for the in cr eased fl am e fr ont trave l di st an ce . As co m bustion front propag ati on time is proport iona l to bore size, th e larger e n g i n e r equire s gr eat er ignitio n adv a nce. In fa ct ; th e Yamah a MX adva nce d at a is lin ear with resp ect to . . bore size: TIming (BTDC ,mm) = (.01667)x Bore(m m) + 1.122 mm. Aft er th e boring operati on , the ports must be cha m fere d in order to prevent snaggin g the rings on the sh a r p p on edges. This is the o pport u ne time in which to perform a bit of intellig ent port work. First , do not alter the transfe r ports or th e inher ent angles. Changi ng this may result in a det eri oration of th e loop scaveng ing effect. The exha ust port · should be raised to 1.55 " from TD€~ and the co rners squared . The transfe r rises should be knife-e dged, but do not cu t th e divider s ba ck . The intake tract sho u ld be lowered to 4 .4 8" below 1 DC, and a si x- pe t a l YZ reed assem b ly installe d. The greater wid th of th e YZ re ed cage requires some increas e in intak e tract wid th . The installa tion of a 36 mm Mikuni will com plimen t th e ' modific a tions, a nd th e O EM (stoc k) jett ing is a good sta rti ng point. A Webco head is highly recomm end ed , cu t a s previou sl y' dis cu ssed . T he final tou ch was a SUN "snake" pip e tuned to this design. Pipe and porting dimens ions wer e work ed out by Dr. Kirk Colli er, Profess or of Mechan ical Engine ering. University of Maryla nd. The result is a "400" cc engi ne c a p a b le .o f strong and reliabl e. operati on . tractab le . yet quick. An import ant aspect of the modific ation is that all wearing parts are sta nd a rd Yamah a. The cost is low, particu larly if one has a ma chine shop at their wa s Specia lty work dispos a l. perform ed by David Valente , Proto Cycle, 713 Sea m e Street , Tempe , AZ. PRIOR TO I MN:HINn£ - !'\1M WIlE --1I\A 1 , a:: ~ ~ It's not su pposed to go into effect until Fe bruary I, 1977 because U. S. Forest Service regula tions are being revised; howeve r, the Seq uoi a Nat'L Forest off-road .vehicle (O RV) Pla n is in print. and av ailable from the U ,S. Forest Service at 900 West Gra nd , Po rt e rvill e , CA 93257 , The p la n include s generous open areas in the" Isa b ell a /Green h o rn , range L a ke region , large networ ks of designa ted • loop trails in the high meadows, a nd only a few outrigh t closure s The Sierra Club and its lawyers m ay challen ge the plan through the U .S . Forest Service appea ls proced u r e . Co n ce rned organiz ations should be aware of this . lea rn what they ca n of the a pp ea ls process , and be p re pared to use the process in the Plan's defense .

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