Honda CB450 K5 Hi tech twin

Old Bike Australasia - - CONTENTS -

1965 was a big year for Honda. The com­pany lured the world’s top rider, Mike Hail­wood, away from MV Agusta with a deal to con­test the 250cc, 350cc and 500cc World Cham­pi­onship classes for the 1966 sea­son, and boldly ven­tured into the ‘big bike’ mar­ket with its rev­o­lu­tion­ary CB450. To­day, the 450 is re­garded as a mid­dleweight rather than a big bike, but back then it was aimed di­rectly at the seg­ment of the mar­ket so long the do­main of the Bri­tish big twins.

The par­al­lel twins of­fered by BSA, Tri­umph, Match­less/AJS, Nor­ton and Royal En­field were them­selves aimed not so much at the home mar­ket, but the USA, where they cut se­ri­ous in­roads into Har­ley-David­son’s ter­ri­tory. Honda wanted a chunk of that, but ini­tially at least the CB450 failed mis­er­ably in USA, due more to the styling that the spec­i­fi­ca­tion. Iron­i­cally it was a big hit in the UK. The poms loved it so much they even nick-named it the Black Bomber, de­spite the fact that it was also avail­able in red. There’s no doubt the new 450 was a spir­ited per­former, and when it was re­leased in Fe­bru­ary 1966, it en­joyed a size­able price ad­van­tage over the Bri­tish 650s, sell­ing for just £350 in UK. Early road tests showed the 450 could sail past the magic ‘ton, which was not bad for an en­gine of just 444cc, but there were other is­sues that se­ri­ously po­larised opin­ion. The Amer­i­cans hated the look, par­tic­u­larly the humpy fuel tank. It was no light­weight ei­ther, tip­ping the scales at 187kg – 20kg more than a 6T Tri­umph. And who­ever se­lected the ra­tios in the four-speed gear­box was clearly out of step with what was re­quired. Around town, the 450 was a chore, with an ul­tra-low first gear (18.58:1) and a yawn­ing gap to sec­ond (10.79:1). This was not so much a prob­lem when chang­ing up – the torquey en­gine bridged the gap nicely – but chang­ing back from sec­ond to first in traf­fic was akin to throw­ing out an an­chor. Ground clear­ance was a prob­lem as well, both the footrests and cen­tre stand eas­ily made con­tact with the road when the ma­chine was heeled over. Seek­ing to prove the CB450’s worth on the race track, Honda, via its UK dealer net­work, tried to en­ter the ‘Black Bomber’ in the pres­ti­gious Brands Hatch 500 Mile Race in 1966 – but the en­try was ve­toed when the F.I.M. (who con­trolled the In­ter­na­tional reg­u­la­tions for the race) banned it on the ba­sis that it was “too ad­vanced”! Clar­i­fy­ing the rea­sons for their cu­ri­ous de­ci­sion, the or­gan­i­sa­tion stated that the use of dou­ble over­head camshafts in a pro­duc­tion ma­chine re­quired spe­cialised ser­vic­ing tech­niques that were be­yond the av­er­age owner and not in the spirit of Pro­duc­tion Rac­ing.

It was seen by many as a back-handed com­pli­ment, and by oth­ers that the home fare was some­what prim­i­tive. Honda did man­age to steal some thun­der by fly­ing in Mike Hail­wood from the pre­vi­ous day’s Dutch TT, and he was per­mit­ted to cut a few ‘demon­stra­tion’ laps on the CB450 prior to the start of the 500 Mile Race.

That en­gine, with its much-ap­pre­ci­ated elec­tric starter, fea­tured a 180º four-bear­ing crank­shaft, twin over­head camshafts and highly un­usual tor­sion-bar valve spring­ing, which en­abled a 9,500 rpm red line – un­heard off for a big twin at the time. Nat­u­rally, much was made of the tor­sion bar valve spring­ing by the ex­cited press, but in re­al­ity a con­ven­tional valve spring is ac­tu­ally just a tor­sion bar wound into a he­lix. Nor was the idea all that new. French Pan­hard Dyna cars of the early 1950s fea­tured such a sys­tem in their 850cc op­posed-twin en­gines. Honda also tried the sys­tem in their V12 For­mula One en­gines, but dis­carded it in favour of he­li­cal springs. In the CB450, the camshaft lobe acts di­rectly onto the rocker arm, while the valve is re­tained by a forked arm which it­self is an­chored to the tor­sion bar. The bar sim­ply twists along its length to pro­vide spring­ing. One side ef­fect of the sys­tem, not en­tirely de­sir­able, is very high seat pres­sure, and the valve spring tor­sion bar also has a very fi­nite life; shorter than he­li­cal springs. There is, how­ever, a sav­ing in weight over the nor­mal he­li­cal spring and col­let ar­range­ment. In a de­par­ture from usual Honda prac­tice, the camshafts were sup­ported in bear­ings con­tained in

end plates on the cylin­der head rather than run­ning di­rectly onto the cast­ing or by the ball bear­ings used in the CB77. Crankcases were hor­i­zon­tally split, with the crank­shaft sup­ported in four roller bear­ings.

The im­pres­sive spec­i­fi­ca­tion failed to trans­late into sales in what was in­tended to be the pri­mary mar­ket, USA. Honda Amer­ica’s Na­tional Ser­vice Man­ager Bob Hansen lob­bied the fac­tory to pro­duce a rac­ing ver­sion in or­der to demon­strate the model’s per­for­mance ca­pa­bil­i­ties, and the re­sult was a small batch of hand-built rac­ers that were en­tered for the 1967 Day­tona 200. They were fast all right, record­ing 137 mph on the bank­ings, but all four en­tries suf­fered prob­lems of var­i­ous sorts.

A gear up

Rev­o­lu­tion­ary as the CB450 was, more work was needed, and by Novem­ber 1967 a com­pletely new ver­sion, the K1, broke cover at the Earls Court Show in London. Most im­por­tantly, a fifth gear was added, vir­tu­ally be­tween the ex­ist­ing first and a slightly raised sec­ond (12.58:1), which trans­formed the rid­ing ex­pe­ri­ence as there was lit­tle need to go back to first other than for a com­plete stop. There were changes within the en­gine too, with larger in­let valves (up from 35mm to 37mm) and ex­haust valves (from 31 to 32mm) and com­pres­sion in­creased from 8.5:1 to 9.0:1. In search of a smoother power de­liv­ery the Kei­hin CV (con­stant vac­uum) carbs dropped from 36mm to 32mm, but de­spite this, power rose to 45hp at 9,000 rpm.

LEFT The CB450 en­gine unit was com­pact, but tall and heavy. BE­LOW The CB450 camshafts bear di­rectly onto hard­ened strips on the cam fol­low­ers, with a sep­a­rate arm re­tain­ing the valve which is con­trolled by a tor­sion bar shaft. BOT­TOM The tor­sion bar con­trol­ling each valve twists in­side a hol­low tube.

New badges for the K5. Kei­hin CV carbs were dif­fi­cult to tune on the orig­i­nal model but im­proved from the K1.

Newspapers in English

Newspapers from Australia

© PressReader. All rights reserved.