Cycle News - Archive Issues - 1960's

TECHNICAL MASTERPIECE photog rap lly : Da rryl No re nbe rg a nd Eric Rickm an Valve sp ring torsion bor t?'= ::n t;;~J~ Sp ring reta iner Th e new est 'w r inkle in valve is th is tors ion bur se t up th a t i!{ lig h t , co m pac t , aHcl eliminates s u rtje. T o r s io n bar is a bou t t he size of a p en cil .. on e e m f a ncho rs in head , th e other in_ide a sleev e that relays , s prin g actio n to f ork that g, -ips and loads va lve s tem, Th ere wa s no audible i" d ien ti o" of ,'all'e fioat , Co m ev e" ", he" she sig " ed off at 8900 rev s . W ith th e throt tl e aga in .t th e sto p, th e ~50 sou" ds mor e lik e a little Offy tho " a m ot or cycl e. I t's app, -oL for 'ed AMA Class C fia t t ra ck wi th _ 0~5 ma x imum ove rbore ( i s oe«) ill uiesoocc class. .~]J l' i ll g S im p ulse s of t he opposed -t hro w cran k, as compared to t he perfectly even-s pa ced impulses of t he si de -by-side arrangement, would be less apt to crea te obj ecti ona ble high frequen cy vibrati on at speed. You mi ght com pa re it to th e old arm y t ri ck of march ing the troops rout e- st ep ove r a bridge of qu estionable st re ngt h. Bu t they sa y n o, t ha t physi cal config u r a ti on , rather than firing interval , is th e primary conce rn , that t he 180 ' cr a n k ha s intrinsic balan ce in the first ha rmonic, and no harmonics ca n be ba lanced wi th a 360 ' u nit. I fi gure anothe r possi bl e advantage wit h th e 180 desi gn: crankca se pres sures wou ld appea r to be lower, as well as more stable, since one piston is going u p while t he other is goi ng down, a s oppos ed t o t he side-byside pist on arran gem ent where both pistons go down at the s ame time and would th erefor e seem t o cre a te more cra n kcas e pressure. Of co urse bot h d esig ns in cor porate cra nkcase breather s, but th e a dvan t a ge in thi s insta nce would st ilI seem to lie with the 180 desig n, es pe cially at high rpm. The H onda 450 b reat he r , incidentally, is up th rou gh the ca m chain cavit y in t he ce n ter ot the engine, a larg e chamber that traps vapor fa ll-out and ve n ts only p r essu rized air out the rear cam cover via a plastic hose. HRlII 's te st mac hine showed a mo re not iceable v ibra ti on point betwee n 55 a nd 60 m ph a t fir st, but af te r 500 miles of break-in , t he v ibes van ished as if by m a g ic a nd it's been smoot h as silk si nce th en - you fig ure th a t one out. Splined t o th e r ight s ide of t he crankshaft, j ust inboard of t he ce nt rif ugal oil filt er , is th e small straight-cu t prima ry d ri ve gear th a t t u rn s t he gearbox ma insha f t vi a a la rger mating gear on t he ad jacent clutch hub - no prima ry chain to adj us t. But at t he other end of th e cr a nks ha ft is th e pa rt tha t win s f ri ends and influences pe ople, the electric st a r te r mecha nism . On th e cranks ha f t , immediately outsi de the engine ca se propel' , is a f r ee-wh eeli ng sproc ket with a n in tegral outboard flan g e ; th e sp ro cke t is cha in-d ri ve n from th e nea rby st a rte r mot or while it s protrud ing fla ng e nests in a sm a ll centrifugal clu tc h th a t is key ed t o th e cra nksha ft and in ternally spring-loa de d t o g r ip th e fla ng e on t he f ree-tu rni ng s p r ocket. Thus, when t he s t a r te r motor chain t u r ns th e sprocket, the centrifugal clu tc h turn s t he crankshaft to which it is keyed ; but as the engine fir es and rpm ri se ab ove crank ing speed, ce ntrifuga l force pull s t he gripping sp ringloaded bearings in the clutch a way fro m t he engine sha f t sprocket fla n ge , pe r mitting t he sp roc ket to come to res t on t he sp inning sha ft . A ct ual ly , t he cen t rifugal clu tc h is not ke yed di r ectl y to th e cra nks haft but is sc re we d to t he back side of t he a lt e rna to r ma gnet body which is keyed to th e ex t rem ity of t he crankshaft . T he s ta r t er s it s directly ah ead of t he e ng ine and it s torque is clev erly mult ipli ed, in addition to the diff erentia l between its chai n drive sprockets, by a set of sun gears inside th e s t a r te r motor housing itself. And sinc e th e starter wo rks direc tly off the crankshaft the engine can be electrically started in an y gear a ft e r disengagi ng th e cl ut ch. I'm t ell in ' ya , the re's so me fin e engineering in t h is li t tle j ew el. N ow let 's ge t on to th e r eall y t ri cky st uff up sta ir s. On t he wa y up we note th at t he a lloy cyli nde rs ha ve iron a llo y s leeves ; th ey house t hree-ring , domed a lumin um pistons accommodati ng a bore a nd stroke of 70 x 57.8m m ( 2.8 x 2.3 inc hes) . A g reate r part of t he he mi sp here combustion chamber is t aken u p by big va lves wit h in t a ke and ex ha ust seats of 35mm and 31mm closi n g on 8.5: 1 compression. Bot h valv es incorpor a te hard s tellite fa ces and stem tips and sea t in a th ick s teel combustion cham be r liner of a bo ut 'A-i nc h de pt h t hat is cast r ig h t into th e alumi n u m • • .. • . • • •

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