The cylinder head is by far the most interesting part of the bike. DOHCs control two valves per cylinder through rockers sat on eccentric shafts that can be turned to adjust valve clearance. Valve springs are replaced with torsion bars set at right angles to the valves and controlling them by another set of rockers. In 1965 when this style of head was first used in the CB450, valves springs were just not up to coping with the high revs and large valves of the 450, they would bounce the valves right into the pistons; in 1975 when the CB500T was launched valve spring technology had advanced to the point where, along with Ducati's Desmo head, such niceties were all but obsolete.
This was, I suspect, especially pertinent to the CB500T because unlike the earlier bike it was not unknown for the torsion bars to break and the valve to hit the piston with consequences that were both expensive and far from amusing. The CB500T also suffers pistons made from alloy more useful for making Coke cans than withstanding the thermal and mechanical stresses inherent in large, high revving vertical twins, while the only good thing to be said about the gudgeon pins was that they wore out before the small ends, that were expensively part of the con-rod. The entire bottom end will be well known to anyone who's had a look inside one of the early seventies 250 or 350 Honda twins. A huge four bearing crank holds pistons moving out of phase, drives a five speed box through a multi-plate clutch and is generally quite tough. The gearbox has all the precision of a NSU Quickly box but rarely fails.
The frame is basically similar to the CB450, which was the role model for the CB250K, and its single down tube design would not look out of place around any number of British motors. The engine is firmly clamped in four places and must greatly aid the strength of the chassis. Only the design of the seat tubes and welded on swinging arm brackets give cause for concern, and the swinging arm is also rather flimsy. The wheels are spoked and the excellent drum front brake was dumped for an indifferent disc that didn't, etc., etc.
The styling was something else. The seat was pinched from a Velo, the tank a cross between a WD Triumph and god knows what else, while the whole exhaust system must have been conceived by an apprentice Heath Robinson and executed by a designer urgently in need of a cataract. operation in both eyes. Ugh!
The nice lump of an alloy motor kept people from completely collapsing in hysterical laughter, while the modicum of low down stomp and mild kick in the pants at six grand could turn laughter into a scowl on the face of rival street racers. The handlebars were high, the footrests too far forward, the seat uncomfortable and the vibes below five grand too intrusive; as if Honda had learnt absolutely nothing in the ten years of evolution of the CB450 (the last bikes were apparently rather good, with all the performance of the first bike and much improved handling and braking).
Driving slowly in town the bike felt much worse than a Triumph twin, the torque reaction along the crankshaft (from out of phase pistons) thrumming the tank and bars, the CV carbs providing a jerky response and despite wide bars, the front wheel requiring much muscle to shoot around ill placed autos. The CB500T had gained thirty pounds and steering geometry more suited to straight line stability than flickability, also suffered the usual non-damping shocks and low grade forks (they were slightly better than the elastic band items fitted to the 1965 CB450). A combination that made the bike uncomfortable in almost every situation, bu one that never became terminal or evinced any wild speed wobbles unless you did silly things like ride on worn tyres with the wrong pressure.
Take the Honda for a cruise down the motorway, there's no trouble up to 75mph, but go beyond that to find a need for the back muscles of Atlas and a weave queasy enough to induce sea sickness. OK, you can bung on some decent shocks and uprate the forks with heavier oil and stronger springs, that'll take out most of uneasiness, but the whole caboodle is less taut than the CB450 and generally inferior to any number of other Jap middleweights. As with the 450, there's enough chassis rigidity to preclude any real nastiness, but with ten years life behind it, it's just not good enough.
Flicking the Honda through the bends was about as much fun as playing Space Invaders after having both hands amputated. As soon as the thing is heeled over the centre stand attempts to out do even the council's efforts at ruining the roads by digging up huge chunks of tarmac, while the floppy forks do a pogo act that would find top billing in any half decent circus. Ahem, again, those aforementioned suspension mods will tighten up the plot, dumping the stand regains not unreasonable ground clearance and fitting flat bars and rear-sets afford a more ergonomic riding position that aids decent weight distribution. But whether all this effort is actually worthwhile will depend on how much faith can be placed in the durability of the engine. As the 500 has the same bore as the 450, it might be possible to use its superior pistons, although the effect of their higher compression on different valve timing might well reduce reliability rather than improve it.
Although there are a few useful two-into-one exhausts around, just about all the tuning shops stayed well clear of the CB500T because of its poor reliability, so there's no easy way to uprate the engine specification. That said, used fairly mildly the motor does stay together for around 30000 miles, but it does need an oil change every 750 miles to make that kind of mileage.
Servicing is simple and needs no special tools - in fact, the whole motor can be stripped down in an afternoon with a fairly basic tool kit. Neither the valves nor contact breakers require frequent adjustment, the latter often needing less frequent replacement than many major engine components. Unlike the 450, fuel depends on how the bike is ridden. As much as 70mpg is available if you insist on riding it like a restricted 125 or as little as 45mpg if you run along at max revs all the time. 50mpg is fairly easy to average.
Unfortunately, those who want to ride economically will find themselves blitzed by vibration while those who insist on a smooth life will find themselves cruising at around 7000rpm and drinking fuel as if the North Sea had unlimited reserves. A sort of compromise exists around 6000rpm, just under 70mph in top, when the motor has just started to smooth out and fuel averages around 55mpg. Tyres and chains last for average distances for middleweight performers. As much as I dislike to admit it, something like Honda's very own CB400 Superdream is in almost every respect a superior machine - a claim it could certainly never make against a 1965 CB450, let alone the final update of that design.
Both of the ugly silencers can last for an unfortunately long time and even the dumpy balance pipe (surely borrowed off a forty ton truck or something) doesn't dissolve in its own rust for three years. The single front disc has the same performance characteristics as those on the CB250RS and CB400/4. Need I say more?
The brown paint fades away to the same kind of colour the British army would doubtless like to use to paint army barracks, while the bright orange alternative would only please those little minded men at the Ministry of Motorcycle Safety (or Abolition, depending on your point of view).
Natch, all the chrome turns to rust and the external alloy to white dust. The front forks leak oil just slowly enough to get the bike through an MOT. The electric starter's out of the action after about 15000 miles, although the rest of the electrics don't give much trouble. Unless you've owned a CB450 you probably won't have much feel for the potential of the engine. It is in theory a classic design, let down in practice by penny-pinching in the production department. It looks awful, corners badly, is often unreliable and doesn't go very fast. But it's very cheap and the engine has a lot of soul.
Bill Fowler