To eliminate the stresses and extra mass of bolts required to make a head gasket work, the iron cylinder liners were screwed into the two heads. Each head with its downward-projecting cylinders was then slid into place. Only two or three years earlier, Aurelio Lampredi had pioneered this technique at Ferrari, and today it is again used in Formula1.
This was a two-valve engine with a very modern, narrow, 58 degrees between the intake and exhaust stems. The result was a flatter, faster-burning combustion chamber than the 90-100-degree chambers of rivals Gilera and MV. Why buck the trend? Guzzi had found a power advantage in the narrow valve angle in its Singles. The V8’s four cams were driven by narrow, delicate spur gears in a case on the engine’s right side. All valves seated directly on the aluminum alloy head material, no seat inserts. Bore and stroke were 44.0 x 41.0mm, the very dimensions Honda would in five years choose for its four-cylinder 250s.
The agony began with the machine’s first appearance, at the 1955 Belgian GP, where the studs securing the crankshaft main bearings broke. Look at these engines from below and you will see nine plugged holes that allowed access to these fasteners. In the fall of 1955, it was decided that replacing the original 180-degree crank with a 90-degree would cut stress on main-bearing webs, and two variants were evaluated. The first cranks were one-piece forgings, with con rods, inner main bearings and roller cages split for assembly over it. Although this seems makeshift, it had been a successful method of construction before WWII, used even by Mercedes for its mighty 600-hp supercharged GP cars.
The V8’s “shakedown year” was planned as 1956, but the shaking never stopped. The tally was water-pump failure, broken big-end cages (while leading at Hockenheim), unscrewed tappets, a collision, a stoppage, overheating while second to Geoff Duke’s Gilera, then a crash in a national race and a big-end failure at the Monza GP des Nations. Not one finish. Meanwhile, Guzzi’s super-light 350 Singles dominated their class.
Next, cranks were ordered from the leading German specialist, Hirth, who also supplied Gilera. Roller cranks were still thought best for racing motorcycles. The open question was, is it stronger to use a built-up crank with one-piece rods and non-split bearing cages? Or is it stronger to use a one-piece crank with split bearings and rods? Great 1930s rivals Mercedes and Auto Union had stood on opposite sides of this choice, each tempted by problems to try the other’s solution.
The usual built-up crank is made by press-fitting crankpins into the flywheels, but pressed joints—even when assembled with tons of pressure—creep apart under high-frequency vibration. The Hirth assembly system consisted of radial face splines cut into one end of a hollow crankpin and into its mating flywheel. Once the one-piece connecting rod and its big-end cage and rollers were in place, pin and flywheel were powerfully drawn against one another by a large internal bolt, whose threads in the pin were of different pitch from those in the flywheel. If this seems arcane, consider that the 2800-cubic-inch piston engines on Martin and Convair airliners of the 1950s had cranks built in the same way.
To make the Hirth couplings strong enough, crankpin diameter had to increase by about 50 percent, to 30mm. This, in turn, resulted in a hefty assembly of sixteen 5mm con-rod rollers and their cage. As a crank turns, the speed of a crankpin bearing varies as the rod swings forward and back around the wristpin. This twice-per-revolution variation can be too much for a heavy roller assembly to follow. The result can be skidding, overheating and failure. To reduce the speed variation, the con rods were made exceptionally long, with a 2.6:1 rod ratio.
Carburetion was another issue. Eight magnesium Dell’Orto 20mm carbs, cast and machined by Guzzi, lived in the cylinder Vee like interlaced fingers. At first they were served by two float chambers on the left, but poor running soon forced provision of one tiny float chamber for each carb.
Guzzi’s fairings were made by a remarkable craftsman who annealed the magnesium material between hammer-forming sessions by covering it with soap, then heating it until a certain color change occurred, showing that the hammer-hardened metal was again soft. All exhaust pipes were the province of another specialist who filled them with sand, its internal pressure adjusted from time to time by taps on tapered pins as the metal was made to yield by wise application of a torch flame. Try learning that from a drop-down menu.
