Wednesday, 11 January 2017

Honda CBX750


As originators and long time advocates of the in-line four, Honda must be wondering just what hit them, as they gradually faded out of the big bike ballgame from the late seventies onwards.

Suzuki captured the market in reliability and Kawasaki took on the heavy performance mantle leaving Honda with nowhere to go but down and out. While the K2 series gave a useful boost in power, they were also heavy, ponderous and somewhat lacking in the reliability that was the hallmark of the original, late sixties, K series bikes.

When Honda finally got their act together by launching the CBX in '83, it was, in many ways, just too late. The CBX was burdened with Honda's reputation for self-destruction gained by their vee fours and a history of making each new foUr inferior to its predecessor.

This is all rather fortunate for potential purchasers of the CBX because its lack of popularity has forced down new prices, and, in turn, left used prices seriously depressed. An '83 model can be picked up privately for not much more than a grand. For such money the CBX offers a lot of serious motorcycle.

The engine is a clear evolution of the original four. There are some definite areas of improvement and some areas that may cause concern to the long term owners.

The DOHC head is quite a neat design with each of the valves having its own camshaft lobe and rocker. The rockers are balanced between valve and a hydraulically controlled piston, that makes setting valve clearances unnecessary. I have my doubts about such a system, but as some engines have done over fifty grand without any apparent problems I can't really complain.

Some camshafts lobes are quite heavily scored by thirty grand, but this is rare, while camshaft bearings don't seem to suffer even if the bike doesn't get its regular three thousand mile oil change.

A hyvoid chain from the centre of the crankshaft drives the camshafts. The tensioner is automatic and despite looking dangerously similar to the one used in the vee four actually works quite well. A couple of bikes need a new camchain by around forty grand but I've heard bikes with fifty grand on the clock that still sound quite quiet. So Honda seemed to have sorted out this problem on the CBX.

The crankshaft has a straight out gear machined into the web for primary drive. This is situated inboard of the left hand outer piston. I would have preferred it on the end of the crankshaft where it was more insulated from the shock of the piston moving up and down, but GS Suzukis use the same setup with no problems so I'll just have to accept it. The gear mates with a weird and wonderful clutch. The clutch has a split gear that in theory takes up any backlash in the primary drive, but in reality will tend to develop excessive wear as the machine ages making the transmission both jerky and noisy. As Honda were able to machine their engine cases with sufficient precision to use proper straight cut gears as long ago as the early sixties I find this incomprehensible.

The clutch also boasts an equally dubious mechanism that lets it slip if engine and road speeds are mismatched on down changes. The other nasty is an alternator rotating at twice engine speed. The alternator has been removed from the end of the crankshaft and resituated under the carbs. Honda, who are famous for making engines with quick wear chains, have tempted fate by running the alternator using chain from the centre of the crankshaft. Lack of a crankshaft-mounted alternator meansthe engine is narrower and the alternator runs in a more pleasant enviroment.

Electronic ignition, run off the end of the crankshaft, completes the picture of an engine that needs minimal maintenance - just a regular oil change and the occasional carb balance.

Honda seemed to have catered to all the areas that are regularly neglected by lazy ageing juvenile delinquents like myself. Even the alternator is not known to fly apart, although the hydraulic clutch does get a bit ratty with twenty five grand on the clock - which serves Honda right for using such a complex design where conventional multi-plate (and non-hydraulic) clutches have proved perfectly adequate in the past.

I've taken so much trouble to define the Honda's engine because it is a relatively unknown quantity on the used market and rather under estimated in terms of usefulness and longevity.

The engine is stuck in a fairly conventional twin down tube frame that uses the frame tube to contain engine oil. All of the 750 fours have had separate oil tanks, so this is nothing new. Dumping the oil tank might go some way to helping keep the mass down to 480lbs, but it's probably more a product of losing weight inside the engine and using plastic on the chassis wherever possible.

The half fairing is neatly moulded into the petrol tank giving the bike an integrated appearance from head to stop lamp that's far ahead of their previous efforts - and even looks quite neat up agalst their fully faired high tech vee fours.

The rider sits in the CBX with a nice chunk of five gallon fuel tank to grip with his knees, handlebars that don't immediately strain the back or wrists and a mildly stated array of instruments held in the fairing. The clutch is light and just looking at the throttle gets the rev counter in the red. First gear engages without any of the usual Honda noise and the bike will move off on the minimum of throttle.

it doesn't exactly go screaming off into the distance, in developing so much power from a mere 750cc Honda have concentrated on delivering most of the go above seven and a half grand. The bike's quite happy at lower revs it just doesn't deliver very many kicks. There's a little surge beyond 4500rpm, but hit 7000 and everything begins to happen very quickly, the silencers make a nasty snarl and the arm stretch effect is quite disturbing.

With six speeds to play with I would have been happy with four - there's many different ways that the Honda can be used. Stick the thing in sixth, and it'll potter along up to about 90mph, when the power will suddenly kick in and get the speedo around to 125mph with no trouble. True top speed works out at about 130mph, but that needs the bike screamed in third, fourth and fifth to obtain the last 5mph. The fairing provides sufficient protection to make 100mph cruising quite pleasant, although wet weather will still penetrate gloves and jacket. It's a lot better than a bare bike.

The suspension is complex but tends to work quite well. The strong front forks are burdened with something called TRAC, which I won't even bother to write out in full. Anti-dive is operated by the calipers on the twin discs in a manner that avoids rational comprehension and, as it doesn't seem to have much effect, can best be ignored.

Alr can be pumped into the forks to improve the springing, although standard settings were fine for my ten stone. Damping is also adjustable, .but with twenty grand needs to be on the firm setting. Rear shock is controlled by Pro-Link. The shock is hidden away but damping is remote controlled via a cable and springing by pumping in air.

This is all rather clever but let down after fifteen grand by the shock which loses most of its damping and a swinging arm that wears at the bearing points. It says much for the integrity of the frame that it still refuses to indulge in speed wobbles.

The combination of weight distribution and steering geometry that the Honda uses means that it feels easy to throw around in traffic and, yet, doesn't get vague at high speeds. Much of this is down to the excellence of the riding position, with footrests placed well back, flat bars and a comfortably shaped seat. The rider feels at home on the bike straight away.

I had the opportunity to swap straight from a CBX to a 1970 CB750, and the difference in feel was quite extraordinary. The two bikes really are decades apart. The CB felt loose, sloppy and imprecise, it needed so much more muscle to ride and the engine felt flat, like someone had switched off two cylinders.

Out on some fast country roads there was no way even a suicide artist could hope to keep up with the CBX on one of the older fours. The CBX still weighed too much and that mass could still catch it out if you tried to change direction too violently on bumpy curves, when the bike would tend to go too far towards the new direction, and a series of small lurches would result. On the CB750 the same kind of action would have the handlebars dancing and the bike lurching off towards the wrong side of the road. On the CBX you can brake, shut the throttle or wave to young ladies while banked over without any problems.

I particularly liked riding the CBX in the rain. There was enough bodywork to give moderate protection to hands, knees and shoulders; the Honda could be used safely in the mild half of the rev range and I never had to worry over the tyres doing something unexpected. The only mild worry was the brakes, which while powerful and, usually sensitive, would occasionally lock the front wheel without any warning. I can only assume that somewhere along the line the antidive was interfering with the efficiency of the units. The rear disc was no better than any number of drum brakes I've used...

In the dry, the twin discs had loads of power, using the CB750's single disc was dangerous in comparison because I'd become used to leaving my braking to the last possible moment and the older four was more likely to go straight through something than stop by the time I'd realised my mistake.

Brake pad wear is not amusing, 7500 miles from either front or rear means three sets of pads at £12.50 a pair. Fuel economy was rather good for the available performance. Keeping below 7500rpm gave an average of 55mpg, with a bike still able to break through the speed limits.

Using all the available power, having the maximum amount of fun, meant economy went down to just over hOmpg, but to get down to this level required some pretty wild riding that would soon be halted by loss of driving licence. Heavy 100mph cruising returned 45mpg and the bike averaged out at 50mpg.

The rear tyre was worn out after 7000 miles and the front after 12000 miles, which in the high performance league isn't bad going. Front tyre is a sixteen inch job, which except for being very expensive to replace, has none of the twitchy nature of some of the wheels of that size on other bikes (who mentioned Suzuki?).

As 750 straight fours go, the Honda comes out leading the pack in the handling stakes. It has the same kind of stability as the old GS range but with much quicker and easier steering, that belies the fact it weighs so much. There is a slight top heavy feeling on first acquaintance with the bike, but this is soon forgotten.

That the handling abilities are exceptional for a Jap bike is quite true, but some kind of true perspective can be thrown in here, by comparing the CBX with either Dresda or Rickman-framed CB750s. Both of these bikes are lighter, just as stable but not quite so quick steering in curves. The comparison is a little unfair as neither of the specials have to cope with the sudden application of power at 7500rpm. I guess that if the old CB had the kind of handling abilities as the CBX the specials would not have sold very many frame kits.

Using a bike with a worn swinging arm, a shot shock, tyres just down to the legal limit and fifty grand on the clock was an interesting comparison with the low mileage bike I'd been riding. The bike was very sensitive to white lines and the back wheel could lose traction over bumpy curves, but the frame;was basically sound enough to take it all in its stride. When the laziness of the local council left a foot deep crater in the road, the Honda twitched the front forks for an instant and then settled down. The rear shocks gave me quite a kick, but at least my body was ideally positioned to absorb most, of its force. This kind of stability out on the edge of suspension, component and tyre wear is very encouraging.

The motor still knocked out that delightful surge of power, but low speed running was a little troubled by carb problems, probably resulting from the owners reluctance to change the air filter. The engine sounded fine, the clutch was a little remote and a little jerky, but nothing a few miles riding couldn't absorb. Problems seem to vary from bike to bike, with no discernible pattern. Some rectifiers have burnt out, some cams worn out, some clutches started slipping, but there seem few instances of the engine blowing up. In the States, where the bike is much more popular, tuned engines haven't led to instant demise.

The silencers last three years and it's a brave owner who opts for non-standard replacements (carb problems become very amusing). The black engine cases lose their shine after two English winters. The paintwork is good for a lot longer and comes up real nice with a bit of elbow grease.

I forgot to mention vibration for the fairly simple reason that I never noticed any.

In performance terms (speed and handling) the CBX is easily the best four that Honda have ever built. It makes the CB750 look like an antique. So far, the motor has stood the test of neglect and crazed right wrists as well as any other big four, whether examples will clock up 100000 miles like the original is another question. I have the feeling that when the over complex components that make up the CBX's engine do fall they will do so in a very expensive manner and a big way. When that occurs is anyone's guess, but I wouldn't be happy buying a bike with more than twenty five grand on the clock.

Nice one, Honda.

Bill Fowler

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