Back in the sixties, those astute designers at Honda cleared a space on their drawing boards for a brand new vertical twin design that formed the basis of not just the CB450, but many of the later, smaller twins that in the mid-seventies seemed to be absolutely everywhere.
The basis of the 450 consisted of a 180° crankshaft supported on four huge main bearings, with an extremely short stroke, and a double overhead camshaft that, in many ways, has more high tech features than modern bikes.
Developing 43hp at 8500rpm, the engine could shoot all the way up to 10500rpm (this was 1965, chaps) and the head was supposed to be safe to twelve grand.
At these kinds of the revs valve springs would have dumped the large valves straight onto the pistons, so each valve had a torsion bar at right angles to the valve, operating through its own rocker to control the valve.
The camshafts operated via another set of rockers that sat on eccentric shafts to allow for (very small) valve clearances. Thus Honda produced a system with all the merits of Ducati's desmo head, without the inclination of separate camshaft lobes for tearing the valve apart. The Honda's valve clearances are also very simple to adjust because the eccentric shafts stick out of the side of the engine, and it's just a screw and locknut arrangement. Gear primary drive to a multi-plate clutch and a four speed box take care of the transmission.
In 1969 the engine had an extra two horses, a wider spread of power and a five speed box. The stroke of the engine was lengthened in the mid-seventies to produce the awful CB500T. This was slower, more vibratory and far less reliable than the older bikes.
The all alloy engine looked impressive in the same kind of way as those Gold Star engines (if I'm never heard of again you'll know that some enraged Gold Star owner has blown me away, although if his shotgun's as reliable as the BSA single then he'll probably do himself more damage). The engine was installed in a single downtube frame that had a passing resemblance to something BSA might have produced in the days when they led the world. This was made from heavy gauge mild steel - as were the mudguards, petrol tank and side panels.
The forks were typical period pieces of Jap technology. Undersprung and underdamped, they twist under heavy braking and bottom over large potholes. The shocks stop the rear wheel from rubbing agaist the mudguard, but nothing much else — unless the owner is exceedingly stupid they will have been replaced (god help us if classic collectors insist on keeping the original suspension on Jap bikes).
The engine gives the bike a fairly high centre of gravity, but the bike has a short wheelbase, which makes it quite easy to flick through the curves on decent tyres (Roadrunners are a good match). Using the steering damper induces a high speed weave, but a stock bike with Girling shocks and heavy oil in the forks is very stable, with no hint of a speed wobble, probably thanks to the heavy frame.
For a 450, the bike is quite heavy at 410lbs, but some compensation is found in the fact that the heavy cycle parts last forever and there's enough metal left to restore them.
The looks of the original model are sufficiently strange to assure it of a place In the classic hall of fame. I really like the hunchback three gallon petrol tank, the speedo/rev counter unit in the headlamp and the clean, uncluttered, functional lines of the machine. It's far enough away from the Jap flash stuff to have the lines of a British bike from a distance.
The main attribute of the Honda engine is that it produces enough power for 90mph cruising, averages 70mpg and has a quite remarkable reliability record. For sure, early engines could write off their camshafts if revved too harshly when cold and with fifty grand on the clock the small ends (con-rod material) will wear enough to let the pistons flap about, destroying the rings and seizing the engine. Between these two events, the engine needs hardly any maintenance except for oil changes at 750 miles.
Lacking anything as silly as balance shafts, the engine avoids destructive vibes by having the pistons moving out of phase with each other. This gives perfect primary balance but produces a torque reaction along the crankshaft. The firing pulses are uneven and some people don't like the resultant exhaust noise but I find it quite pleasant. Vibration is present, especially at low revs in low gears but it fades into the background after a few weeks use. it all depends what you like - if you need to know how the engine's working without constant reference to the rev counter then the Honda is just fine; if you prefer remote, electric smooth engines then look elsewhere.
In three years of ownership the only effect of the vibes was to loosen the rubber petrol pipe, blow one light bulb and help destroy a battery. Nothing fell off the engine or chassis. This is the kind of vibration most people can live with.
The most exceptional quality of the engine was economy. it was easy to average 75mpg and extremely unusual to obtain less than 70mpg. The lack of balance shafts, the highly efficient valvegear, the lack of emission and pollution controls, and the use of twin constant velocity carbs must have all helped to produce such economy. But it was still pretty exceptional to produce such efficiency straight off the drawing board - the UK industry could only approach it after decades of evolution.
The power produced between tickover and six grand was a product of mild low down grunt rather than the kick-you-in-the-pants-break-your-arms type of stuff. The Honda was quite happy to potter along on the minimum of throttle in fourth gear - indeed, at 30mph with the throttle just off the stop, the engine had enough torque to stomp up some very steep hills. Opening the throttle very slowly under such circumstances even produced some mild acceleration.
Above six grand the engine turned out rather more interesting power. In second or third - the bike would really take off, with some arm stretching power that was real good fun. The bike feels more exciting than a mid-seventies 550 four and can take a Yam X5650.
Acceleration from 60 to 90mph In third is where the bike really shines - and where most people do most of their riding. 90mph equates to 9000rpm in third and just under eight grand in fourth. It's easy to get the bike up to 105mph in fourth, getting the last 10mph on the clock is hard work as air resistance is hard to live with, but down on the tank on a long road gets the bike up to its true top speed of just under 110mph.
The stock footrest position is six inches too far forward for the fairly flat handlebars. The tank is high, the seat low, so the rider sits in rather than on the bike, giving a feel of security and one-ness with the machine. Because of the riding position the seat has to take too much of the rider's weight and it's only comfortable for journeys of less than 100 miles. This is a great pity because the large tank and good fuel economy means 200 miles can be covered without bothering with petrol stations.
One of the Honda's minor problems is the fuel filter used for the reserve setting on the petrol tap. Situated at the bottom of the petrol tank it quickly becomes clogged making it impossible to use the reserve setting. This means the tank has to be drained, the tap removed and the filter cleared, every four thousand miles.
Another problem occurs with the clutch that gets upset by riding too much in heavy traffic in town. It starts to drag, maklng neutral impossible to find, and needing use of the brakes to stop it from moving off at traffic lights. I'll always remember the face of a friend with whom I'd swapped a GS400 for an afternoon's ride. Used to the remote and civilised nature of the Suzuki, he looked' very harassed by the Honda's disinclinatlon to behave itself. The solution is to adjust the clutch at the handlebar end to obtain more leverage.
Where the Suzuki was always dangerously remote, the Honda always had enough feedback to inform the rider about the condition of the road. I was glad to get back to the Honda as I just couldn't take not knowing what the engine and tyres were up to.
Although rare on UK roads, I did once meet a fellow CB450 owner. He looked quite astonished when I mentioned how much I enjoyed cruising at 90mph and how you could really screw the thing in third. Apparently, he never went above seventy in deference to the bike's age and rareness. I couldn't help thinking what a waste of such a great engine. Still, takes all sorts...
The bike has TLS drum front brake and SLS rear. In about 15000 miles I never had to replace any brake pads (and god knows how many miles they had done before - there was eighteen grand on the clock when I bought it). The front brake was strong enough to twist the forks (OK, so they weren't too strong in the first place...) and knocked off the speed in a safe and predictable manner. Just think, no locked brakes in the wet, no wet weather delay and no strip downs. In three years the brakes were not touched except for infrequent adjustment at the handlebars to compensate for brake pad wear and cable stretch. The only draw back was that repeated stops from 90mph would eventually cause enough overheating to induce fade. But this was a small price to pay for the low running costs and superior performance in the wet.
The bike was ideally suited to fast country roads where it was light enough to throw around and the thing could be left in third, controlled on the throttle for most of the time - the engine made a delightful growl on the overrun.
The original exhaust fell apart when I was in Brighton - it was twelve years old, please note - a pair of Universal megaphones were purchased and eventually fitted outside the shop (I still have the burn marks). These units made the bike run very lean, under certain atmospheric conditions it was necessary to run with the carb mounted choke slightly on. Using such exhausts without modifying the carbs would eventually have terminal mechanical consequences.
Being a curious kind of chap, 1 once took the engine up to an indicated 12000rpm and can report that beyond ten grand the engine still produces plenty of power, vibration comes up to Tiger Cub levels and I got scared enough of an imminent mechanical explosion between my knees to back off pretty quickly. I only did this once, you understand, just to see if those rumours of the engine being safe to twelve grand were indeed true. As an engineer (of sorts) I would probably be banned from the Institute of Mechanical Engineers if this ever came to their attention, but as I never bothered to join, it probably doesn't matter, anyway. Still that such an old design could out rev later fours of the same size says plenty for the basic engine design and leaves one wondering just how good the older fours could have been if they had similar quality engineering.
My disinclination to replace a worn chain was rewarded with a sudden loss of forward power and a long, character building, walk home. The snapped chain bent the clutch pushrod, but didn't break through the crankcases - an event not entirely rare on old Honda twins — check for oil leaks around the drive chain sprocket. It took four weeks for a new pushrod to come from Honda.
Because the clutch pushrod seal is situated next to the chain sprocket it picks up all the road debris, wearing out after around 5000 miles. Fortunately, the old one can be pulled out with a screw driver and a new one fitted without splitting the engine. Engine maintenance was straightforward and infrequent except for regular oil changes.
The constant velocity carbs needed adjusting every 2 grand to keep them in balance - but this was just playing around with the stop and slow running screws. The one into two throttle cable isn't very clever and unless routed very carefully can have the engine ticking over at ten grand. The points need adjusting around ten grand, but they seem to last for ever. Camchain and valves need minimal attention.
A rear Roadrunner lasts for 10000 and a front for 13000 miles. The cheapest chain available goes for around ten grand. Rear brake pads last for ever, front go for at least twenty grand. That all combines to make the Honda exceptionally cheap to run while still being lots of fun to ride. Indeed, despite owning many much more modern bikes since selling the Honda some years ago, I haven't had as much fun riding a bike since getting rid of it. It was the kind of bike that encouraged you to take the longest possible route between destinations. Perhaps I was just younger then.
It was on one such occasion that things went seriously wrong. Rather than scoot across the Severn Bridge I decided to take the long route via Gloucester, using the twisty A46 where it meets Bath. The engine had been running so well and the sun was shining that it seemed like the only thing to do. Halfway between Bath and Gloucester there was a tinkling noise from the top end of the engine. I pulled over to the side of the road, but there wasn't much I could do to the engine, so I continued at a fairly slow rate. The bike survived until the other side of Gloucester when a sudden loss of power was accompanied by a dense cloud of blue smoke from the left hand exhaust.
A 225cc single cylinder CB450 has very little power but we struggled on towards Chepstow. Getting through Chepstow was hell because of the steep hill In Its centre. This just about finished off the engine, it was down to 20mph with fumes coming out of both exhausts. But it still hadn't failed. This happened five miles from Newport. Oll seemed to pour out of every joint and the blue clouds hung over the road as far as I could see.
Stripping down the engine revealed two holed pistons and scored bores and slightly scored small ends. A rebore plus new pistons and rings cost £50. As the con-rod material was the small end bearing surface, and the con-rods couldn't be detached from the crankshaft, they were not replaced - there wasn't any actual movement. The holed pistons were probably caused by the nonstandard silencers, so not Honda's fault.
The rest of the engine looked in perfect condition, no wear on the cams or in the gearbox. On tickover the rebuilt engine was almost silent, no clatter, no nasty noises.
The Black Bomber is one of Honda's best twins (if not the best, so far) and very, very practical.
Bill Fowler