Secrets of Six
The RC174's complexity made winning simple
Simply put, the 297.06cc inline-six defined Honda's RC174. Without that mighty Wurlitzer of a motor, the bike would barely pique the interest of the most devoted historian.
Likewise, that engine defined George Beale's quest to build an inch-perfect replica of one of Honda's most famous racebikes. From its three sizes of con-rods to metallurgy unknown even today, this totem of Honda's engineering challenged Beale's abilities, his tenacity and his patience. Here are some of the Six's choicest bits.
Japanese multi-cylinder engines may look terrifyingly complex, but such is their inherent design logic that they come apart and go back together with ease. The Six is no exception. JPX's Julian Charnol found that for all its hidden secrets and multitude of tiny parts, the Six was easily reassembled providing sufficient care and time were allowed.
This is not, however, a powerplant suited for garden shed rebuilds. In the '60s, Honda's race shop was as clinically clean as any operating theater, with white-gloved technicians going about their work with fastidious attention to detail. With its Space Age air filtration and controlled environment, the JPX factory is similarly surgical.
Putting the engine together was one thing. Getting it to run as it once had for Hailwood was quite another. "We started with no information at all, no data about settings," Beale says. "At first, whenever we had problems, we had no idea whether it was ignition, carburetion or something else."
After literally years of unrelenting effort, the Six's first dyno run was a bitter disappointment. "It made a pitiful amount of power-as little as 10 bhp," Beale says. "Turned out it was only running on three cylinders. We'd been told by the ignition supplier that we needed only one igniter box and three two-spark coils, which wasn't right. It now runs on two boxes and six separate coils. Later we tried to be clever and map out a full ignition curve. But the thing gains revs so fast that a flat curve is all you actually need, just like the original would have had with its magneto.
"We sorted that, and still got only 33 bhp. The valve guides were too long and obstructing the tiny inlet ports. Julian cut the guides and re-cut the valve seats, and immediately got 50 bhp at 15,000 rpm, and still rising fast. It looks like it ought to give 65 bhp-plus at 17,000 rpm." For comparison this would be 219 bhp/liter, or close to what Honda's RC211V makes.
"All the Sixes you see paraded are running to about 14,000 rpm," Beale says. "That extra 3000 [revs] makes a huge difference to the way it goes-and sounds. And it has to be the noisiest bike ever, even more than the DKW [a shrieking two-stroke nicknamed the Singing Saw]." When George first ran the bike in his garden, a family friend phoned from home to ask who was making "that bloody awful noise." She lives 3 miles away.
"Nobby Clarke, Hailwood's mechanic, says he used to regularly rev the RC174 to 19,000 rpm, even though the factory specified 17,000," Beale says. "Perhaps that's the reason Mike's engines didn't usually last as long as the others."
The man honored with track-testing the Six is John Cronshaw, one of the fastest and canniest classic racers around. His first impression was of the engine's complete absence of flywheel effect. "If you pull in the clutch without staying on the throttle, it just stops dead, even at 10,000 rpm," he says. "So you have to change clutchless. It's like keeping a ball in the air-you have to catch it just right all the time. At present it's a bit more difficult than it needs to be because the carburetion isn't perfect. When it is, it'll be a pretty fast bike."
Cronshaw has paraded the original factory 250 Six. "Compared to the 250," he says, "the spread of power is quite broad, and even the 250 drives right through from 8000 rpm. But it'll take some getting used to not dipping the clutch into corners-you have to drive through everywhere.
"The chassis feels very precise and light. And the engine's so smooth, no vibration at all. It just whistles along, like riding on air.
"With all his talent Hailwood must have been bored out of his socks racing this thing. It was that far ahead of everything else."