Mat Oxley: Yamaha – the V4 grand prix trailblazers

Yamaha is currently building an all-new MotoGP bike, because its current YZR-M1 is no longer competitive. The M1 is powered by an inline-four engine, whereas the all-new machine will be powered by a V4 engine, like the rest of the grid.

There are various reasons why MotoGP’s other four manufacturers – Aprilia, Ducati, Honda and KTM – all use V4 engines. Most importantly because a V4 should make more power – shorter, more robust crankshafts, fewer main bearings and so on – plus the dynamics of a V4 work better in battles, which are now the norm in MotoGP. The M1’s only advantage is superior cornering speed, which it can’t use when fighting in the pack.

It is ironic that Yamaha is the last manufacturer to build a V4 MotoGP bike, because the Iwata-based company was the first to successfully introduce the configuration to grand prix racing, way back in the 1960s.

The 250cc RD05 and 125cc RA31 were miracles of miniaturisation, which was the primary engineering focus of the wild technology race behind the so-called golden age of grand prix racing. Throughout the 1960s Yamaha raced two-strokes against Honda, which led the race for ever-higher rpm with its six-cylinder 250 and five-cylinder 125 four-strokes.

“I didn’t know the meaning of the word ‘sleep’. All-nighters were common”

Yamaha mechanic Ferry Brouwer worked on Phil Read’s 125 and 250 V4s, helping the Briton to a world championship double in 1968. The Dutchman has fond and not-so-fond memories of the tiny RA31, which had a bore and stroke of 35 x 32.4mm.

“I didn’t even know the meaning of the word ‘sleep’,” says Brouwer. “Working to three or four in the morning at races was normal and all-nighters were common. But I was only 19 and it was a dream come true to have that job.”

The RA31 V4 engine was a work of genius and frighteningly complex: two crankshafts, induction by rotary valves and 22mm Mikuni carburettors, its peak of 44 horsepower (that’s 336 horsepower per litre) hidden between 15,500 and 17,000rpm, those screeching horses (no silencers!) delivered to the rear wheel via a nine-speed gearbox.

“The engine was very, very compact, so there were many little things you had to be very careful with, like the piston rings which were only 0.6mm thick,” Brouwer adds. “You had two crankcases, one for the lower cylinders and one for the upper cylinders. There were so many gears – each crankshaft ran into an idler gear, which ran another gear, then into another for the ignition, so you had a lot of backlash to deal with.

“Setting the ignition timing was a hell of a job because each magneto ran at half engine speed, with a twin cam driving the contact breakers. Cylinders one and four fired together and cylinders two and three fired together, but the contact breaker for number one was on the upper magneto and number four was on the lower magneto, so you had different backlashes to deal with too.

“Then, of course, the cams wore, but not at the same rate, so you’d have one opening at 0.35mm and the other at 0.4mm, so that would alter the timing. And then the fibres on the contact breakers all wore at different rates too. Getting all four cylinders as close as possible could take two hours.”

The V4 had an appetite for pistons and crankshafts, so it was just as well that Yamaha had worked out ways to simplify the engine’s maintenance.

“You could change cranks while the engine remained in the frame, which was quite radical,” explains Brouwer. “You took off the barrels, the disc-valve housings and the top of the crankcase and there was the crankshaft.

“Sometimes we would fit new pistons before a race. Again, Yamaha were very advanced – the pistons were coated with a kind of green silicone. We’d warm up the bike, let it cool down, warm it up again, let it cool down and take off the cylinders. Then you could see the high spots on the pistons where the silicone was worn. We’d sand them down with an oil stone to prevent seizures and that’s how they went into the race.”

The RA31 was also tricky in the extreme to ride, with that 1500rpm powerband and iffy carburation, further complicated by the two-stroke oil mixed into the fuel. If the engine ran too rich it oiled its sparkplugs and the bike spluttered to a smoky stop. That’s why Yamaha tucked a set of spare plugs and a plug spanner inside the fairing. And if the engine ran too lean it overheated, seized a piston or crankshaft and ejected the rider over the handlebars.

No wonder that some wary riders nicknamed these highly strung two-stroke GP bikes ‘Whispering Death’.