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..... ~ ...... ...... 10-< o 0.. ~ Rocker arm pivot is machined on an eccentric shaft. A hydraulic capsule (inset) uses engine oil pressure to rotate the shaft. and therefore move the pivot to adj ust valve cl earance. A ball-check valve locks the capsule . a single 40mm valve co ntrols th e exha ust flow. The valv es are ope ned by three separate rocker arms, which rid e against a sin g le-overhead camshaft. Each roc ker rid es on its own cam lobe. T o minimize maintenance, the big Sh adow uses th e same hydraulic va lve adjusune n t system pioneered on th e smalle r Shadow. For this svstern, each roc ker-a rm's pivo t is m;lchined o n a separat e ecce ntric sha ft. When th e shaft is rotated, the rocker-a n n 's p ivot point moves 10 increase or decrease valve clearance, A hydraul ic capsule, ener- gized by engine oi l pressu re, ro tates rhis sha ft 10 bri ng th e rocker arm agai ns t th e cams haft and val ve stem. Once the rocker has been ro ta ted to this posi tion - zero valve clea rance - a ba ll-c hec k valve locks the ca p- sule iruo pos it ion. As long as engine oi l pressure is maintained, the ca p- sule maintains perfect (zero) valve clearance a t a ll engine tempera tures, In th eory, thi s system is fool -proof. When th e en gin e is sta rted from dead co ld, it lakes just o ne valve cycle for the ca ps u le to pressurize with oi l, rot at e th e rocker shaft, and take up excessive valve clearance. Si nce th e oi l is supplied through bleeder orifi- ces, t h e hydraulic ca p su le can' t develop enough press ure 10 hold a valve off its seat. Of co ur se loss of engine o il press ur e wo uld disrupt the system . .. but then valve clearance wo u ld be way down on th e list of engine trou ble. T wo 36mm Keih in downdraft ca r- burarors brea the th rough a common air cleaner. The carbs a re constan t- vacuum type, and Honda employs a comp lia n t elas to mer diaphragm mat erial th at a llows rhe ca rb slides 10 move with virtuallv no resistance. T his mat eri a l ha s proven its elf on Honda ' s •' :-Iour a nd, Cold Wing engines, and provid es for lighming fast ca rburetor response, eliminati ng the need for accelera tor pumps. Aspecia l fuel circuitautomatically enriches th e fuel mixture under high manifold vacuum (trailing throule on deceleration) 10 prevent backfir- in g. The system works; dedi ca ted ki ll -sw itch antics arc requir ed to coe rce the big Shadow in to backfir- in g, T his sys tem ma y gain impor- tance in th e futu re if backfir e-sensirive ca ta lytic co nverters become common on street bikes. Sinre a hem ispherica l combustio n chamber mak es it diffi cult to co nt ro l detona tion in a big-bore engine, two spark p lugs arc used for each cylinder. T he plugs are posi tio ned along the sides of the combus tio n chamber, and are fired sirnu lta neouslv 10 crea te two separate flame fron ts. 'ensuring smooth and rapid combustio n. In spi te of the huge pi stons and the 9: I compression ra tio of the II OO Shadow. than ks to thi s design its engine wi ll d igest regu la r-grade unleaded ga so- lin e without compla int. The ign iti on sys tem is ba u erv- powered a nd fu lly transistorized.T he spa rk-advance curve is electron ica lly derived from engine rpm, with Ha ll - effect sensors to trigger th e spark - th ere a re no mechanical parts in th e system . Timing sta rts at 5° BTDC initial, and advances starting at2,200 rpm, reaching a peak of 24° BTDC total advance at 4,000 rpm, Each cylinder has its own ig ni tion co il, wi th tw in leads firi ng th e two plugs. T he ig ni tion circuitry is su ch that bot h coi ls would normall y fire with everv crankshaft revolution - crea t- ing not on a power stroke. While th is isn't a problem on an in liue four. on a big-inch V-twin wit h generous val ve overla p the was te spark could cause backfirin g, To amid that, Honda a" waste" spark a t th e cylinde r (Below) The Shadow's unique hydraulically-assisted clutch. Arrow shows clutch piston. Note light diaphragm spring in foreground . ins talled a separa te Hall-effect sensor on the rea r cylinder's camshaft, sig nal- ing th e ig ni tion compurer to ca ncel th e unnecessary spark. When designing th e starting sys- tem for th e new big-inch Shadow, Honda engineers found that th e elect ric sta rte r and th e starter com- ponents would have to be h uge. T he problem was th at if th e big V-twin kicked back on starting, convention - all y-sized sta rter components co uld be shattered . A sprague (one -way) cl utch, as used on the cl utch basket of th e 700ccShadow, wouldn' t help: the kick-back for ces destructively load th e starter Rear-train in th e same d irec tion as the cra n king forces. In stead of usin g a Mack-t ru ck-sized sta rter, Honda in stalled a miniture multi -p late diaphragm-s pring cl utch wi th in . the ~ tilrter gear train. If th e engine backfires on starting, thi s small cl utch slips, preventing damage to th e sta rt ing system. The engine is water-cool ed, with cooling aided by the oi l jets under th e pistons. Shallow (mostly cosmetic) cooling fins a re also on th e cylinder and cylinder head, An electric fan is posi tioned behin d the lower hal f of th e radiator, a n d a utornat ica l lv switches on when th e svsrern reache~ 200° F. Unli ke some 'other wa ter- co o led street bi kes, th e Shadow's cooling fan only runs when the igni- lion is swit ch ed on, The crankshaft is machined with stra ight-cu t gears to dri ve an all -new diaphragm/hydraulic hybrid clutch. As is now common on ma ny street bikes, this clutch is ac tua ted bv a hydra u l ic ma st erv' s lav e cy l inder system . . 13

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