Cycle News - Archive Issues - 1980's

~ o ...... ...... ..... 10-< 0.. ~ Rocker arm pivot is machined on an eccentric sha ft. A hydraulic capsule (inset) uses engine o il pressure to rotate the shaft. and the refore move the pivot to adj ust va lve cl eara nce. A ba ll -check va lve loc ks the capsule . a sing le 40m m valve co ntro ls th e exha ust flow. Th e valv es a re o pe ne d b y three separate ro cker arms, whi ch r id e again st a sin g le-ov erhead ca ms ha ft. Each roc ke r rid es o n it s o w n ca m lobe. T o min imize m aintenance, th e big Sh adow uses th e same hydrau lic va lve adj us u ne n t system pioneer ed o n th e sma lle r Shado w. Fo r thi s svste rn, each roc ker-a rm's pivo t is m ;lchined o n a separat e ecce n tric sha ft. Wh en th e sha ft is rotated, the rocke r-a n n 's p ivo t point m ov es 10 in crease or decrea se valve cl earance, A h yd raul ic caps u le, energ ized by e ngine oi l pressu re, ro tates rh is sha ft 10 bri ng th e rocker arm agai ns t th e ca ms ha ft and val ve stem . Once the ro ck er has been ro ta ted to this po si tion - zero valve clea ra nce - a ba ll-c hec k valve loc ks the ca p sule i ruo pos it ion . As lon g as engine o i l p ressure is m ainta ined , th e ca psu le maintain s perfect (zero) va lve cl ea rance a t a ll e ngi ne tem pera tu res, In th eory, thi s system is fool -proof. When th e en g in e is sta rted from dead co ld, it lakes just o ne valve cycle for th e ca ps u le to pressurize with o i l, rot at e th e rocker shaft, and take up excessive valve cl earan ce. Si nce th e oi l is supp lied through bleeder orifices, t h e hydrauli c ca p s u le ca n' t devel op en o ugh press ure 10 hold a valve off its seat. O f co ur se loss of engine o il press ur e wo u ld disrup t the syst em . .. but then valve cl earance wo u ld be way dow n o n th e list of engine trou ble. T wo 36 m m Keih in d ownd ra ft ca rburarors brea th e th rou gh a common a ir cleaner. Th e carbs a re co nsta n tvacuum typ e, a nd Hond a employ s a com p l ia n t e las to m e r di aphra gm m at erial th at a llows rh e ca rb slide s 10 m ove with virtuallv no resistance. T his mat eri a l ha s proven its elf o n H ond a ' s •' : -Iour a n d , Cold Win g engines, and pro vid es for lighming fast ca rb u re to r response, elim inati ng the need for accelera tor pumps. A spe cia l fuel circ u it automaticall y enric hes th e fu el mixture under hi gh m an ifold vacuum (traili ng throul e o n d ecelerati on ) 10 prevent ba ckfi rin g. Th e syste m works; d edi ca ted ki ll -sw it ch anti cs arc requ ir ed to coe rce the big Shadow in to ba ck firin g, T h is sys te m ma y gain importa nce in th e fu tu re if back fir e-sens i rive ca ta lytic co n verters beco m e com mon o n street bik es. Si nre a hem isph eri ca l com bus tio n c ha m ber m ak es it d iffi cult to co nt ro l d eton a tion in a big-bore engine, two spark p lugs ar c used for each cy linder. T he plugs are posi tio ned a lo ng the sides o f the co m bus tio n c ha mber, a nd a re fired sirnu lta neous lv 10 crea te tw o se para te fla m e fron ts. 'en su ring smooth a nd rap id com bust io n. In spi te of the huge pi stons a nd t he 9: I co m pression ra tio o f th e II OO Sh ado w. tha n ks to thi s design its engine wi ll d iges t regu la r-g rade unleaded ga solin e with out co m p la in t. Th e ign iti on sys tem is ba u ervpowe red a nd fu lly transistorized . T he spa r k-adva nce cu rve is electron ica lly derived from engine rpm , with H a ll effect sensors to trigger th e spark th ere a re no mechanical p arts in th e system . Timing sta rts at 5° BTDC ini tial, a nd ad va nc es starting at2 ,200 rpm , reachin g a peak o f 24° BTDC to ta l ad va nce at 4,000 rpm , Ea ch cylind er has its o w n ig ni tio n co il, wi th tw in leads firi ng th e two p lugs. T h e ig ni tio n circu itry is su ch that bot h coi ls wou ld normall y fire with everv cra n ksh aft revolu tion - crea ting " wa ste" spark a t th e cy linde r not o n a po we r stroke. Wh il e th is is n' t a proble m o n a n in liue fou r. o n a big-in ch V-twin wit h generous val ve o verla p the was te spa r k cou ld cause back fir in g, To am id that, H o nd a a (Bel ow) The Shadow's unique hydraulically-assisted clutch . Arrow shows c lu tch piston. Note li g ht d iaphragm spring in foregrou nd . ins ta lle d a se pa ra te H all-effect sensor o n th e rea r cyli nder's ca ms haft, sig naling th e ig ni tio n co m pur er to ca nc el th e unnecessary spa rk. Wh en d esigning th e starting sys tem for th e new big-inch Sh adow, H ond a e ng i nee rs found that th e elect ric sta rte r and th e starter co m ponents would have to be h uge. T he problem was th at if th e big V-twin ki cked ba ck o n startin g , co n vent io n a ll y-sized sta rter components co u ld be shattered . A sprague (o ne -wa y) cl utch, as used o n the cl u tch basket of th e 700ccShadow, would n ' t hel p : the ki ck-back for ces destructively load th e starter Rear-train in th e sa me d irec tio n as th e c ra n k i ng forces. In stead o f usin g a Mack-t ru ck -sized sta rter, H onda in stall ed a min iture m u lti -p late d iaphragm-s p ri ng cl utch w i th in . the ~ tilrter gea r train. If th e engine backfires o n starting, thi s small cl utch sl ips, preventing d amage to th e sta rt ing system. Th e e ng ine is water-cool ed, with coo lin g aided by th e oi l j ets under th e pistons. Shallow (mos tly cos me tic) cooli ng fins a re a lso o n th e cy lind er and cy linder head, An elec tr ic fan is posi tioned be h in d the lower hal f of th e radiator, a n d a ut orn at ica l l v swi tches on when th e svsrern reache~ 200° F. U nli ke some 'oth er wa terco o le d street bi kes, th e Sha do w 's co o lin g fan on ly ru ns w hen the ign ilio n is swit ch ed on , The cranksha ft is m achined with stra ig h t-c u t gears to dri ve a n a ll -new di aphragm /h yd raulic h ybrid clutch. As is n ow co m mon o n ma n y street bikes, this cl u tch is ac tua ted bv a hy dra u l ic m a st er v' s lav e cy l i n de r system . . 13

• Cover