Riding with the GODS

Honda's six-cylinder CBX was not the quaint aberration it's regarded as by many today. When launched in 1977, it was a stunning demonstration of what the world's largest motorcycle manufacturer was capable of - and John Nutting was there.
WE all have those defining moments when we can remember just where we were at a pivotal moment in time. Such as when JFK was assassinated, Elvis died, or when I heard the news that my hero Jarno Saarinen had died with Renzo Pasolini at Monza in 1973.
And so I can recall with crystal clarity the moment when I was told about the imminent launch of Honda’s phenomenal CBX. It was during an evening press presentation after we’d been trying out the CX500 vee-twin at the Nogaro racing circuit in France in the summer of 1977. We were handed monochrome photographs showing an across-the-frame six-cylinder road bike. We were gobsmacked. It couldn’t be true.
Six-cylinder machines of any kind were the stuff of dreams. I’d seen the shrieking 250cc and 297cc sixes that Mike Hailwood and Jim Redman had raced during 1965 and 1966 when I’d been to the Isle of Man TT. They were beyond reach, ridden by Gods.
Yet here we were, being told that soon we would be able to ride, on the road, a 1047cc 24-valve six developing 105 bhp at 9500 rpm in just a few months time. It took a while to sink in.
I had about five months to prepare myself for the moment, but at the press launch at Honda’s Suzuka circuit in November 1977 it was nothing less of a shock to see the bike in the flesh.
It was the first time that Honda had hosted a launch in Japan. It was taking no chances. The CBX was the top of a new range of machines that included revamped twins and 16-valve dohc fours and the unusual CX500, a pushrod watercooled Guzzi-styled vee-twin.
More than anything else Honda wanted to prove that it had the technological resources to master any kind of engine format. At the time motorcyclists were lusting for bigger fours that handled more confidently than in the past. Suzuki and Yamaha had revealed their GS1000 and XS1100 models. Honda went one better. The words Honda and six became synonymous again.
Monster bike
THE first question that begged an answer was how could such an engine be mounted in a motorcycle and leave enough room for cornering clearance? Back-of-envelope calculations suggested that 64.5mm (2.54 in) diameter pistons pitched at the required 1.4:1 spacing for an aircooled engine would require a width of at least 60cm (23.5 in) across the fins. Yet that wasn’t much different from the Suzuki GS1000’s width.
Cleverly, Honda’s project chief Masahuri Tsuboi took a leaf out of Shoichiro Irimajiri’s design thoughts with the original racers.
He mounted the generator and ignition systems on a shaft behind the cylinder block, through which the drive was taken from the forged one-piece crankshaft by an inverted-tooth chain and thence by gears to the clutch and five-speed gearbox.
To shave precious inches from the cases for cornering clearance, the outer webs of the crank were chamfered along with the cases. The weight of the cylinder head with its four valves for each combustion chamber was reduced by using hollowed camshafts.
Remarkably, the engine didn’t impinge on the rider, apart from the view of the cam covers poking out either side of the fuel tank. The cylinders were canted forward and the six 28mm-choke CV carbs mounted in a vee-shape as they entered the airbox, although this reduced the volumetric efficiency of the outer cylinders, as the jetting variations showed.
Wasp-waisted, the CBX was slim across the nose and footrests and, with canted-back handlebar forgings, felt eager to go.
Even with an all-up weight of 558 pounds (think about that, about 100 more than a Hyabusa) the CBX felt light to steer and snapping the throttle open made the engine respond suddenly with a symphony of melodious exhaust sound. It was crisp, tight, smooth and immediate. I felt like I was about to ride with the Gods
Retrospectively, it’s hard to believe that the designers were happy to provide the CBX with spindly 35mm-diameter fork legs, tiny brake discs and fibre bushings for the swinging arm.
Yet they did and the assembled bike journos happily applauded the handling. The steering was neutral and the cornering stable right to when the footpeg tips were skimming the road. We were so overwhelmed by the experience that the incipient weave induced by modest bumps was regarded as only a minor irritation.
Daily dream ride
IT was more than six months before I was able to find out if the claims of a 140 mph top speed were really true. Day-to-day use of Honda UK’s metallic red test bike was as undramatic as you’d expect, except that this time you had to face a constant barrage of questions every time you stopped. No problem, just part of the responsibility of being a bike God.
Changes from the prototypes I rode at Suzuka included a different cylinder head with two additional studs and 20 percent softer springs on the rear shocks. These were adjustable with three rebound damping rates and two for compression. Ride comfort was improved but the changes did nothing for the rear end’s waywardness on choppier surfaces.
The conditions on the MIRA timing straight in July 1978 couldn’t have been much better, with a slight downhill tail wind to provide that always-welcome boost to the top speed which could be used to silence bar room arguments.
Not that we at Motor Cycle, the weekly paper, resorted to exploiting one-way figures... much. Sometimes, for example when the Laverda Jota broke through 140 mph, it was worth trumpeting the fact. But for making worthwhile comparisons between bikes of their top speed, only the two-way average had any meaning because the effects of gradient and wind were more or less cancelled out.
Only on the rare occasions when there was a severe cross wind, which reduced the speeds in both directions, or when there was standing water on the road surface, did we postpone the testing.

Building up the brakes

Yamaha RD500LC
IT is time to construct a set of steel hoses for the front brakes. It’s possible to order the bits ready made but this is a simple job using parts readily available from your local dealer.
If you measure up from the master cylinder to each caliper, allowing for some slack, the steel hose can be bought by the metre. The fittings come in all sorts of finishes from the standard chrome type seen here to stainless and aluminium anodised and most are available from stock.
Care must be taken too ensure the hose end is cut square and the steel outer is swaged back enabling the fitting of the collet. Once assembled, the relevant hose fitting can be tightened up ready for the final part.
The only dodgy bit when working with this stuff is the potential for getting a stray bit of steel wire down the back of your fingernail. It is a good idea to put some kind of protective coating on to the hose to prevent the outer rubbing on things like the mudguard or my nice shiny new frame.
There are many ways of doing this, from plastic wrapping that can be added after construction to ‘heat shrink’ that can be applied before the ends are fitted. Either way it will keep the hoses from damaging anything and also create a more professional finish.
With the calipers now reassembled and mated to the new hoses we can start to get the brakes working as they should. It is far easier to bleed a ‘modernish’ system like this off the bike as it is crucial to have the master cylinder pointing downwards to allow the air to rise.
A lot of people mistakenly try to bleed downwards. This is not only laborious but also impractical, far easier to let the air rise naturally back up into the reservoir. If you try to bleed down, every time you tighten the bleed nipple the air starts to rise again and can get trapped at the end of the master cylinder.
By attaching a piece of clear pipe (never use battery breather pipe as it has a split every few inches to allow the battery to breath even if the pipe kinks) to the bleed nipple and returning the other end into the master cylinder reservoir, you can go one stage further by allowing the fluid to circulate freely.
Another aid to bleeding is a is a ‘bleed bolt’. This is a cheap and handy bit of kit that will also save a damaged caliper if the original nipple has sheared off. It simply replaces the bolts that hold the banjos in place and enables the bleeding of virtually any part of the system.
You will find that the system will bleed up very quickly this way and prevent and fluid wastage. Of course, once the brake is properly bled and pumping up well, the fluid can be changed later by simply letting it drain out while topping up the reservoir with new fluid.
This is how they do it at the factory and it has worked for me over the last 20 years.
I have started to polish the front fork bottoms and I must admit they do look rather nice.
A previous owner had actually powder coated them but luckily the thick black coating literally fell off when attacked. The aluminium of the fork leg was easily polished up, first with 1200 grade wet and dry and then Solvol Autosol.