Memorable Motorcycle: Honda RC148

February 18, 2013
Frank Melling
Frank Melling
Contributing Editor| Articles|RSS

Our Memorable Motorcycles expert, Frank Melling also is the organizer of the British vintage motorcycle extravaganza known as Thundersprint. Melling began riding five decades ago and remains as much in love with motorcycles as when he drove his first bike into a cow shed wall aged ten. In the last 50 years, Melling has competed in every form of motorcycle sport and now declares himself to be too old to grow up and be sensible.

Five Cylinders and Just 124cc

No one with a love of motorcycle racing can be in the presence of Honda’s tiny RC148 and not be awed. Compared with the electronic sophistication, and immaculate finish, of a modern GP bike, the Honda looks almost like an extremely well-made, home-built special – until the statistics are reeled off. A normal rev limit of 21,500 rpm – and another 500 rpm still left for the last lap dash to the line – eight-speed gearbox and a race weight of 85 kgs (187lbs) mean that the Honda “5” was the absolute limit of motorcycle engineering in 1965.

In every race, the Honda sounded as if it was operating on the last 1% of what a motorcycle could achieve before it self-destructed – although in fact it was utterly reliable. By contrast, the iconic Honda 6 always produced calmer, more controlled mechanical music – like a tenor singing soprano – while the “5” was a wailing, frenetic, Punk Rock lead singer.

What is all the more remarkable is that the RC148 was designed, manufactured and built largely without the aid of computers. Go to a GP today and the IT gurus are more important than the mechanics but in 1964, Honda’s race staff were able to achieve remarkable feats of engineering with nothing more than a mechanical slide rule, log tables, a drawing pen and a notepad.

They also had an enormous advantage over modern designers: they sensed the engineering in the same way that a top chef feels exactly the amount of seasoning required to make a culinary masterpiece. The RC148 came at a time when spring makers could judge the precise temperature of piece of red hot metal by spitting on it and watching how their saliva reacted.

The RC148 did not simply appear on a sheet of paper in Honda’s drawing office: the Tokyo factory had a lot of experience of very high revving, multi-cylinder engines stretching all the way back to 1959 and the RC142 Twin which revved to an astonishing, for the day, 14,000 rpm.

However, by 1965 Honda was facing huge challenges from the two-strokes of both Suzuki and Yamaha. The battle raged across all the small classes – 50cc, 125cc and 250cc – and Honda were determined to defend the four-stroke cause.

The key to the “5” was Honda’s highly developed 50cc Twin which had a bore and stroke of 34mm x 27.4mm. Two of the Honda pistons would fit on a credit card and with room to spare. Each of the four valves which fed the cylinders weighed less than 10 grams – or the same as a couple of grapes.

With a bore of 34mm, Honda hit on the idea that 5 x 25cc cylinders would become a world beating 124cc engine – in effect, two and a half 50cc Twins.

Honda knew a lot about getting minuscule cylinders to fill effectively, and very high revving engines to stay in one piece and so were comfortable with an engine spinning routinely to over 22,000 rpm and they were also very familiar with the eight-speed gearbox needed by the 125cc to keep it within the 1000 rpm power band.

The chassis followed standard Honda practice by using the engine as a stressed member in a duplex spine formed from steel tubing. Brakes were twin leading shoe drums – but aided by the excellent engine braking which the Five provided the moment it was shut off.

Rhodesian Nobby Clark was the only non-Japanese mechanic to work on the “5” and remembers the bike with fondness.

The Honda Five is wafer thin and represents the limit of
motorcycle engineering in 1965.

“I liked the ‘5’ a lot – except for having hands which were too big! Everything was so tiny that parts disappeared in my fingers, the parts were so small. The valves looked more like carpenters’ nails than poppet valves from a motorcycle engine.

“The ‘5’ was a really nice bike and very reliable. We refreshed the motor every 800 km (500 miles) with a new crank, pistons, valves and so on but the eight-speed gearbox was left alone.

“People used to ask me for a piston for a souvenir but we always destroyed the crown because the design was top secret. The pistons arrived from Japan part finished and we filed them by hand, and then satin finished them with emery paper, to match the squish band in each individual cylinder head.

“This was an enjoyable job because part of my annual trade test for Rhodesian Railways was to file a 1-inch square section of mild steel round within a tolerance of 5 thou (0.005” of an inch) so working on the pistons was not a problem.

“More out of caution than need, we would change the clutch about half way through a season but it never really needed it.

“The cycle parts were totally reliable. There was no real suspension adjustment available and the main work was cleaning the brakes regularly and we would change the steering head bearings after a wet race because they tended to get water in them.

“The only real problem with the bike was that it was really sensitive in terms of carburation. This is why Luigi (Taveri) never went well on the ‘5’ in the Isle of Man. The difference in altitude between the lower sections of the course and the Mountain was enough to prevent us getting the carburation exactly right and so the ‘5’ always ran rich.

“The Japanese had mixed feelings about the ‘5’. They liked the bike but they looked at Bill Ivy, and the four-cylinder Yamaha two-stroke, and thought that the writing was on the wall for four-stroke GP bikes – at least in the smaller classes.”

So much for the magic ingredients but what was it like to ride the “5”? We turned to Honda’s most successful racer in the lightweight classes, three-time World Champion, Luigi Taveri. 47 years after he last raced the five, the eyes of the elegant Swiss 82 year old light up at the mere mention of the “5”.

“For me, the ‘5’ was the best of all the Hondas I raced. It was the most difficult to ride but also the most satisfying. I beat the best riders on the best 125s in the world so I can only think good things about the ‘5’.

Master and machine. A three-time world champion, Luigi Taveri
has fond memories of the little Honda “5”.

“It was also the most difficult bike to ride. Even starting it was very, very hard. In those days, we had push starts. I would pull the bike against compression in first gear and the moment the flag moved even a millimeter I would be off. But even surrounded with noise and tension you had to have a completely clear head because the ‘5’ was incredibly difficult to start. The moment the bike fired you had to catch the engine with the throttle and then just feather the clutch until the motor would run cleanly – maybe 18,000rpm.

“After I retired, Barry Sheene tried a lap on my ‘5’ and he couldn’t even start the bike although he had raced Suzuki 125cc Twins.

“The ‘5’ was a beautiful bike to race. It handled very well and was extremely reliable but it had to be kept between 21,000 rpm and 22,000 rpm to be at its best.

“It would rev on safely beyond 22,000 but it went slower and below 16,000 rpm there was a good chance it would stop running all together.

“The noise was incredible. After a race, I couldn’t even hear Tilde (Luigi’s life-long wife and friend) speak to me. Even on the following morning, I couldn’t hear anything.

“The ‘5’ gave me my happiest memories but I now have to wear two hearing aids!

“I enjoyed a very, very close and happy relationship with Honda and I am still in contact with my old GP mechanics even now.

“When I decided to retire, Mr. Honda gave me a 250cc ‘4’ and a ‘5’ as retirement presents and I could not ask for more.”

Luigi was by far the best of Honda’s factory riders on the small bikes and other members of the team remembered the “5” differently. Honda Team Captain, Jim Redman said: “It was a real b$&*!rd to ride. I hated it. The bloody thing cut out every time you looked at it and I still don’t know how Luigi ever managed to get it to go as fast as he did.

“It was also tiny and I couldn’t fit on the thing. Give me any of the ‘4s’, or better still my ‘6’ any day of the week.”

And as our conversation finished, Luigi beamed and asked me the question I had been praying for. “You want to try the bike?”

I am not excessively tall for road racing at 5’10”, and I am well used to threading myself on classic bikes, but the “5” really was a struggle and bits of me stuck out everywhere. This was more than a minor problem because racing the “5” in its GP heyday meant completely disappearing behind the fairing and there was nowhere to complete this conjuring trick.

Even when I did squash myself in my immediate thought was that it must have been agony in the long, GP races of the 1960s. In particular, raising my head when it was on the gas tank so that I could see through the windscreen was almost impossible. When I mentioned this problem, Luigi smiled and explained how he had managed to achieve this feat of contortion.

“I had a full size model of the ‘5’ made and put it in front of the TV. So, instead of watching TV from the couch I lay flat out on the model until I taught my neck to bend back.

“It worked and I could stay crouched throughout the whole race so that was good.

“But now I can’t move my neck properly so the wonderful ‘5’ destroyed my hearing and my neck! But it was a wonderful machine. I wouldn’t change a moment of my time with it.”

And that’s what it takes to be a three times World Champion…