Cycle News - Archive Issues - 1970's

FACTORY REPLICA Foal' ho es • I ehead FRAME MODS By Geoffrey Wood Photos Courtesy "Mot or Cycle." London. England Hond a h as pion eere d several concepts In th e contem porary motorcycle scene which h ave combined to gIve t h em a repu ta tion for techn ical ex cellence. One o f these was the use o f fo ur valves per cylinder on th eir wo rks GP ro ad racers beginning in ) 9 59 . But th e use of fo ur valves per cylinde r is n othin g new. T he idea has been aro und a long, lo ng , tim e. In t he moto rc ycle fiel d , t he first significant use of a fo ur -valve head was by Sir Harry Ricard o on his T riump h sin gles wa y back in the ear ly 19 2 0's. Th is was follo wed by th e fa mo us Rudge singles, wh ich won bo th the t 930 Junior and Sen ior Isle of Man TTs using Four -valv e heads. Rudge also used th e four-valve idea o n pr oducti o n singles up until th e company fail ed in late 19 39. In th e au to motive field , the use of fou r valve s per cy lin der has been eve n m ore widespre ad - at least in racing engine s. Man y Fo rm u la One Grand Prix engi ne s have used four va lves and even her e in Am er ic a, the fa mo us Offenhauser fo urs o f man y years ago were fo llo wing this lin e o f design . Why , then, if th e idea is good in racin g en gines, has it tak en so lon g to be ad op te d for roads t er p ow er plants, o r even o n production ra cers ? T he fir st " mode m " use o f fo u r val ves w as o n the 1964-6 5 Honda "replica" road racers. On st reet b ik es, th e cre d it goes to the Honda XL -25 0 single intro du ced a few years ago. Both bik es were , a nd are, very successful. Perh ap s t he main reason why four valves have not been used m ore is that n o o ne took the ti me to research th e co ncept , then develop a truly su perior engine. Up un til the 196 1 Honda GP b ikes hi t the scene, there was no evid en ce th a t fo ur valves per cy lin der offered an advantage. Hon d a di d the researc h o n port shape. valve lo ca tio n, size, and breathi ng . When th ey had fini sh ed , th ey b uilt the m ost t echnicall y sophisticated fo ur-stroke racing engines of a ll time. It was j ust a m atter of ti me unt il t hey applied the idea to produc tion models. An other rea son wh y fo u r val ves were n ot adopted soone r is t he cost , which is high er due 10 th e ex tra casting and machine work th at mu st be done . Increased a fflu en ce aro und th e world plus i m p ro ve d m an ufa c t u r in g te chniques hav e recently comb ined to so lve thi s problem. how ever, so th a t now we a re se eing m ore four-valv e mo d els co me o n to the market. There ar e several advantages to four valve s for four strokes. On e is th at the valves arc very light co m pa re d to a larger p a ir or val ves. The va lve gear ca n ch amber per p ow er s tro ke, wh ich results in m ore power . T his is p ossible eve n with less lif t to th e valves, which aga in low ers th e load on th e valve gear since less sp ring pressu re is required t o control th e valves . Perhap s th e greatest advan tage of fou r valv es is in high speed performan ce , yet od d ly eno ugh, it is th e impro ved low speed performance th at is m o re desirable to the road racer. By carefully d esign in g th e intake ports , Honda has fo und that a p roper in te rnal gas flow in the com b ustio n c ha mber can b e ac hieved to su p press d et onation. With mo re gas flowing in to th e co mb ustion chamber a t lo wer revs an d sw irling aro und in a flow pattern tha t is less apt to det onate, th e low sp eed to rq ue of an engine is greatly im prov ed. T he cooler exhaus t valves also help on th is, which co mb in es to provid e a high com pression road ster en gin e that squeezes th e last ou nce of p ow er and ec o nomy o u t of each d rop o f fu el o ver an unbelievably wide rev ran ge. Honda also d iscover ed in th eir early GP engi nes th at t hey co uld o b ta in m ore pow er with th e use of four valves. By usin g proper porting and valve timing, they w ere ab le to cha rge th eir cylinders up to a high er level due to the greater valve po rt area in each cy linde r. This soon gave t he m a power advan tage over th eir rivals for th e World Ch ampionshi p . An o th er ad vantage was th e wid er sp rea d o f power, o r lac k o f " me gap ho ni tis " tha t was so co m mo n the n on other * HELI·ARC WELDED * CORRECT SPRI NGS, SET UP KONI SHOCKS, ALL WE LDED ALLOY AIR BOXES ALSO AVAILABLE 3635 W. Mc Fadden Aven ue Santa Ana. California 92704 / Evel says, "I bet my life on E vel Knievel MOl1J rcy cl e Chemi cal s by Technical Chemi cal Company . 1 can't afford to use anythin g but the best." Gasket cemen t Engine degreaser Air IIller 011 Tire mount tube Chain lube P olnls cl eaner Pen etrating oil Starl ing lIui d 4-<:ycl e oil 2-<:yc le oi l Fork oil Gear oil A II-purpose grease 4-<:yc le additive 2-<:yc le additive T ire sealant Motorcycle paint H and cleaner NOW III AVAIL ABLE. m nnlC L A cnEMICAL CO. 10m S'A*lCUI II euus. HUS. 15120 Manufactured and distributed by Te chnical Chemical Co m p any to begin th eir opening much soone r th an in the Ho nda eng ine, since the two valves had 10 have m or e lift to ge t t he ma xim um amou nt of port area. It ta kes time to open a nd close a valve, of course , and t he higher a valve is lifted dealer inquirie s invited . 10737 ~an gl er Road, Dall as, Te xas 75 220 Telephone ( 214) 241-1421 Bill London, VP Marketing Best dealer margin, point 01 sal e display, promoti on and ad allowance . the sooner valve accelera tio n mus t begi n . The pr oble m w it h open ing the in let valve so early is that the exhaus t pressure tends to go o ut both the intake an d exha us t p o rt - th u s ca usi ng the lumpy runn in g and mi ssin g at lo w and m edium e ng ine speeds for w h ich racing engines have hist ori cally been kn own . By u s i n g f o u r smal ler valv es, Honda found t hey could use less lift. o pe n th e va lves la ter. ge t as mu ch peak 13347 W. Wash ingt o n Blvd . power o r m ore, a nd ha ve less prob lem (213 ) 390-3406 w ith lumpy runn in g a t low er engine speeds . The b enefits to th e ro adst er engine Send $3 .00 l or 256 c ol o rful page cata log with mor e than 5500 items, a rc n ot so mu ch in p ea k powe r, but rath er in term s of a broader sp read of pow er th at includes smoo th running down low in the rev range . Th ere sh ould temper ature will a lso he low er . an d t hus provide lon ger va lve life. A no the r advantage is that " u r s mall fo valves ca n offer a grea ter area of op enin g t han tw o valves . It is possib le to litet m o re K3S in to t he com b us rion on the race track ca n benefi t th e m a n on the street - eve n if it does ta k e a few years to sec th e final results. • be less w ear on th e valv e gea r] th e valv e * JIG ALIGN ED racing e ng ines. \Vi th 1\\'0 large va lves it w as n e cessary also b e less wear o n t he ca m s o r ro cker ar ms , since the use of lower spring , p ressu res will h elp prevent the earn sco uring th at h as be come co m mo n in recen t yea rs as spring press u res h ave heen in c reased to co pe w ith in c rease d revv ing ab ili ty, thus be o pe ra te d a t hi gher engine speeds safe ly, which is an ad vantage o n both raci ng: a n d r o ad st er engin es . There will * JUST LIKE ADOLF'S Honda has hel ped show that research RACING FORK OIL • RACING 'ORK Ol • BETTE R HA NDLlNGfDA1\H'E NING • "ROT ECT S FORKS (S EALS-PA RTS OI L LOSS , ETC .) • \l'ILL NOT FOA 1\( O R VAR NISH • MEETS FACTO R Y S PEC S. • SAf. 5, 10 . 20, 30, 40 . 50 & ATF L UBR I-TEC H DISTRIBUTED BY Sa mmy Tanne r Distributing 734 j ' 0 . Avalon Blvd . Wilm inRlon. Calif. 9 0 74 4 Phone: (213)830-4040 Lubricatio n Through Tec hnology

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