1965 to 1975 was a glorious time for Honda, their range of four stroke singles, twins and fours completely destroying the British motorcycle industry and dominating Western markets. The twins emerged as the main machines, though those of a highly cynical nature might suggest that the whole range was based on the engineering in the CB150 OHC single. The latter being doubled up to produce the twins and the fours being nothing more than two of the twins side by side. Honda defined the single camshaft, two valves per cylinder layout, with a massively strong crankshaft running on huge bearings; anyone who tried to copy what was basically a simple (as in pure) design was held back by the impossibility of replicating Honda's production process at a reasonable cost.
At the top of the heap was the CB450, a machine much maligned in certain quarters due to early top end problems caused by revving the motor too hard before the oil had a chance to circulate. A problem intensified on non-standard exhausts when the engine may not run below 4000 revs until warmed. The CB's immediate claim to fame was its DOHC head, with eccentric shafts for the rockers and torsion bar springs for valve control. All in the search for reliable, high rev running. In the quest for finesse the tolerances were very fine, each set of components matched to each other. A quick way to ruin a cylinder head's to mix them up.
Honda eliminated primary vibes by use of a 180 degree crankshaft which ran on four massive bearings to alleviate the resultant torque reaction, a trick Honda have used in most twins over 175cc. The result was rough running below 6000 revs, but sufficient smoothness to cruise at 90mph. The roughness faded into the background after a while, becoming merely a communication that the engine was working away. A stock machine survived the buzzing without trauma (batteries aside) but non-standard components tend to crack up. Frame, seat base, guards, etc were all made out of heavy steel and are replaced with lighter components at the price of potential early demise.
The CB450's tubular frame was strongly constructed from heavy mild steel tube, being a single down-tube type that any number of British motorcycle factories could have knocked up in the fifties. Most of the handling traumas came from soft suspension that should've been modified or replaced by now. Stock, the weave that comes in between 90 and 110mph never turns into a wobble, proof of the basic correctness of the frame layout.
There's plenty of feedback from the road, a complete knowledge of how the tyres are reacting that many a modern bike lacks in the search for sophistication (which usually fades after two or three years when the suspension wears out). This combination of direct contact with the road and raunchy feel of the engine, qualities well known to riders of old British twins, comes as a shock to riders of modern bikes, where progress can be measured in the smoothness of the ride, controls and engine. A five minute ride won't convince one of the correctness of the CB450 experience but stay with it for a while and a brilliant if brutal bike emerges.
Common faults consist of a nasty clutch that drags after ten minutes in town, leaking cylinder head gasket, short-lived clutch pushrod seal (easily replaced, though), cracked carb diaphragms and manifolds, leaking fuel tank caps and chains that snap wrecking part of the crankcase. The camchain and tensioner are fine as long as the tensioner's given a tweak every 500 miles, which is a good point at which to change the oil. The pistons and small-ends (part of the con-rod) are probably the weakest part of the engine, susceptible to continuous high rev work or running on non-standard silencers. Dropped valves are more a result of poor assembly of the head or valve adjustment than any design fault. The engine and chassis demands chronic 500 mile fettling.
The CB450 ran from 1965 to 1974, although it ceased to be imported into the UK in 1971. Ignoring the first year's model as being too near to a prototype that leaves 1966 to 1967 bikes as the definitive buys, having the curious hump-back looks and motors with wilder cams than later examples. However, thanks to the grey importers and the strange habits of American motorcyclists quite a few examples of the '73/74 models are now turning up in nice condition and with under 20,000 miles on the clock. In fact, the last example of the breed combined all the strengths of the original with a much superior chassis that even managed to drop the passing imitation to a CD175. Expect to pay £750 to £1000 for something nice.
Having perfected the CB450 in its last model it was immediately dropped and replaced by the relatively nasty CB500T, perhaps the first Japanese bike to deliberately create a retro silhouette, albeit one that had most punters passing the sick bucket. Time has not been unkind to the CB500T, once the exhaust was dumped and the chassis resprayed it took on a patina of classic motorcycling. As with most such devices, this was largely illusion, the stroked CB450 engine developing a penchant for ruining its pistons and top end and wholly lacking the ability to cruise at 90mph for hours on end.
Nowadays, the CB500T has butch looks and cheapness in its favour, whilst used mildly its engine can be convinced to run reliably (some CB450 parts will fit). The CB500T was the end of the line for the purity of engineering that Honda created in the sixties, a whole decade or two wasted on poor quality replacements that lacked the earlier combination of power, toughness and fun. The excessive cost of producing the high quality components for the DOHC head was no longer viable or even worth the effort. CB500T's go from £100 to £500, with some quite reasonable examples available at the latter price.
The CB450, in both its chassis layout and engine design, inspired much of the layout of the 1968 Honda CB250K1, albeit in a scaled down form and with a much simpler OHC cylinder head. This was the era when learners could ride 250's without any power limitations and the great scam amongst manufacturers was to claim to break the ton.
The CB250K1, armed with 30 horses and a mere 350lbs to hustle, was one of the first to break through the hype and turn such claims into reality. Not easily, though, needing a midget rider laying prone, a following wind and a long, long descending road. Compared to the self-destruct British horrors, and self-igniting Wop junk, of the time, the Honda was way ahead of the game, and in most respects superior to subsequent Honda 250's. Nor did the Honda share the piston burning tendencies of rival Jap strokers, although its exhaust valves could burn out if not regularly tended.
Other faults were similar to the CB450, though the lower level of vibes gave the bike an easier time and allowed a chassis of poorer quality. For instance, the lower fork yoke's made out of the mildest steel known to man and if you undo both retaining bolts with the front end in place, the yokes will unfurl (letting the machine collapse), twisting and distorting into interesting pieces of metal sculpture. The yokes can then be forced back into shape awaiting their chance to snap!
Perhaps that's the most worrying kind of problem with Honda's of this era. Age and mileage leads to corrosion and fatigue of chassis components. Frames rusting through, suspension studs shearing off, alloy brake drums cracking up, wheel rims rusting through, etc. A very careful examination of the chassis is needed on bikes of this age.
The raw CB250K1/2 was replaced by the classically shaped K3/4, which lost power and speed, marking the end of an era for Honda twins, when each succeeding model improved on the previous one. Instead of extra power Honda were able to offer only a more sophisticated feel, leading eventually to the dead end design of the Superdreams. Rather than pushing their engineering up from the twins to the fours, Honda were only able to revive a genre they invented (or reinvented) by redeploying the high technology of their watercooled fours into the latest CB500 twin.
The CB250K3/4 were not unpopular with learners as there were lots of tuning goodies around to make them go faster; even a big bore kit that could be slipped into a stock engine with no way for the police to spot such a transgression, other than by wondering how a '250' could do 105-110mph! £350 to £500 should secure a very nice example of the 250, a hundred notes something that's easy to renovate.
Honda went the big bore route themselves to produced the CB350 (really 325cc), a bike that turned out to be absurdly popular in the States, given that it was neither fast nor flash. There are many still in reasonable shape left in the USA, some turning up in grey importers at £500 to £750.
The CB350's appeal lay in its reasonable cost, ease of use, cheapness of running and the fact that it had just enough power to stay ahead of the traffic. The simplicity of its lines, and pureness of its engineering, echoed (even fed off) any number of British twins and there was also Honda's reassurance of modernity and reliability. It's interesting to wonder how such a machine would be greeted in the tired nineties if it were knocked out by one of Honda's third world off-shoots and priced at about £2500. My guess is it'd sell even better second time around.
Such fantasies apart, there are a few mildly used examples, as well as the grey imports, in the UK. The key to long engine life being frequent oil changes, gentle warming up of a cold motor and the occasional cleaning of the centrifugal oil cleaner (which, outrageously, needs a special tool). These criteria apply as much to the rest of the range as the 350. The 350 engine can be liberated with a hot camshaft, loud exhaust and rejetted carbs but such is its nature that those inclined towards such carnage would be better off looking for a different model! The 350 being rarer but long lasting than the invariably thrashed 250, it's just as well that the chassis, as well as most of the engine, are more or less identical, making the spares position reasonable.
Many owners of these old Honda's have one or more extra bikes stripped down for spares; for every running bike on the road, ten to twenty others have been stripped, stored or scraped; the point at which buying a ruined example and doing an expensive renovation equals its subsequent sale value (rather than the fantasy figures you may see quoted elsewhere) is far off.
If cheapness of purchase still manages to run through the whole breed, utility of purpose was defined by the CD175. In its later incarnation it was again merely a scaled down version of the 450, but simplified yet further by the dumping of both the electric start and one of the carbs, its basic nature defined by the drabness of its appearance (though these days those souls half blinded by nostalgia might claim its lines as classic) and the fitment of 6V electrics. The latter entirely effective except for the minor problem of not being able to ride at night on unlit roads at more than 20mph.
These seventies CD175's were hardly souls that withstood many tens of thousands of miles of abuse and neglect, even going to the extent of fully enclosing the drive chain and having large enough mudguards to make vintage Harley enthusiasts envious. What they wouldn't do was go much faster than 70mph, which with dangerously soft suspension, quick fade SLS drum brakes and marginal chassis bearings was undoubtedly to the good. These limitations, along with a dubious four speed gearbox, stopped the relentless thrashing that other twins of the day suffered. There are an unexpectedly high number of reasonable CD175's still on the road. Good value, too, at less than 300 notes a throw.
That the CD175 had loads of engine potential can be seen in the CB175, which had twin carbs, electric start, five gears and a much wilder camshaft (also a much heavier penchant for eating valves and camchains). With an 80mph top speed, flash looks and acceptable handling they were thrashed so enthusiastically that there are very few left on the road. There was also an extremely rare CB125 twin that had excellent performance from its high revving engine. Don't expect to find any of these learner legal 125's up for sale.
Earlier CD175's, running from 1967 to 1969, though sharing a not dissimilar OHC design, were only related in an evolutionary manner to the later CD's. The earlier CD175 shared its design roots not with the CB450 but the infamous CB72/77, the 250/305 Honda Dreams that in the early sixties represented Honda's first stab at proper motorcycles (in the sense of having styling acceptable to fickle Western tastes).
Like all of the models that were inspired by the Dreams, the first CD175 had its cylinder canted forwards, the frame lacked any kind of downtubes and the engine acted as a stressed frame member. In the CD's case the frame was a pressed steel affair that along with the bulk of the engine was more than adequately strong, the weakness in the chassis, alas, once again coming from poorly damped suspension and questionable steering geometry. The way to hustle through corners was to keep the CD as upright as possible and lean off the bike. Light weight saved the machine from any terminal traumas, even grinding the stand in corners could be survived with nothing more than a resolute twitch of the body.
These early CD's had one of the weirdest engines in the world, being able to chug out sufficient torque at low revs to convince a commuter he was getting all there was to enjoy, then having a hole in the powerband, which combined with massive gaps between the gears in the four speed box, could only be revved through with utmost determination. Once into the real power, though, the CD transformed its nature, becoming another in a long line of fun, high revving cycles that would put in surprising speeds.
Unfortunately, there ain't many examples of the breed left, the whole engines ruined after 50,000 miles of thrashing. Oil changes aside, like many of the sixties twins, they would happily run on a diet of excess throttle and almost total neglect, thriving on an surfeit of revs and speed.
These sixties twins do have some nasty problems, the worst being absolutely foul gearboxes with more false neutrals than working gears. The electrics are marginal with vibration blowing bulbs. Obscure faults, such as burnt out condensers, can turn starting hard or impossible. Camchains snap on high mileage examples and the top end may suffer from sticking valves and burnt pistons (especially on non-standard silencers). But even in the sixties Honda twins had crankshafts that would've shamed a British 650 twin and gear primary drive.
One of the most likely things to account for poor running on the CD175 was an airfilter stuffed with dirt. As the filter was hidden inside the pressed steel frame it was often neglected for years, totally incapacitating high rev running. Also check that the baffles are inside the silencer and that the crankcase area around the drive chain isn't cracked - the chain hidden inside the full enclosure was often neglected until it snapped.
Surprisingly for a machine of this era many chassis parts were plastic (panels and guards), corrosion most likely to occur in the seat base and petrol tank. The engine was so tough that it'd run and run until wear and old age finally caught up with it, component demise so evenly spread that it couldn't easily be resurrected. Nice while it lasted, so to speak.
The 125SS was basically a smaller version of the CD175 with a flasher set of clothes (though not necessarily more attractive) and an engine that only worked on the back of excess revs, which led to a quick wear top end. In short, it lacked the surprising aura of quality and toughness of the CD175. Its value as a derestricted 125 means that there are still a few neat ones left on the road, able to burn off restricted replicas.
The CB160 was an earlier and altogether more serious twin, but with a twin carb version of the CD175's motor and a frame that bore more relationship to the CB72's tubular trellis than the CD's pressed steel affair. Even running to the sophistication of an electric starter (which meant much superior 12V electrics). Handling was a mixture of a weak back end and vague front forks but mass was low and power at 16 horses sufficient to put 80mph on the clock. Nowadays, it's extremely rare on the road, making spares almost impossible....it might be possible to squeeze a CD175 motor into the chassis, though given the latter's better handling it seems like a damn fool thing to do.
If elements of the CB160's frame and chassis can be found in the CB72, the engines are of a rather different species, though as always with Honda twins of this era the general layout remains constant. For the day, these twins were amazing sophisticated, oil tight and able to cruise at 75 to 80mph with a then unknown smoothness. British twins of two or more times the capacity might be faster in theory, but given a few hundred miles to cover the relentless running of the Honda invariably won out. In the Honda CB72/77 were sown the seeds of the destruction of the British motorcycle industry and they are still useful bikes even today!
Their unique appearance (copied by Laverda for their 750SF, though they had to install antique chain primary drives) and useful performance (apart from gearbox, clutch and handling on worn suspension) means they are chasing classic status with demands for over a grand for quite mediocre examples....
That's rather sad as, these days, most of the sixties Honda twins still on the road are getting to that dangerous stage of self destruction through old age and corrosion. Leave them to the collectors unless a really nice one turns up at a reasonable price. Much better to turn your attention to examples of the seventies twins, especially low mileage ones coming in from the States via grey importers (or hop out there for a look yourself). Something like a CB450 or CB350 still has loads of life and lots of bounce left in it, with the added benefit of cheap classic insurance. On the home front, one of the last CD175's represents a cheap, cheerful and quaint way of bopping around town. Happy hunting.
Bill Fowler