TAMING THE BEAST
The designers of the Vee Six had foreseen the problem of longitudinal torque reaction - that caused by the acceleration of the crankshaft and other engine components. Newton's third law states that "An action is always opposed by an equal reaction: the mutual actions of two bodies are always equal and act in opposite directions". Thus if something (in this case a V6 crankshaft) accelerates in one direction, there must be a reactive force in the other direction to counter it. Blip the throttle of a Guzzi at rest and you will notice that reactive force must come from your right leg to stop the whole plot from tipping over. In a bike with a transverse crankshaft this effect is still present but not really noticeable as it is simply rocking the bike slightly fore and aft.
Laverda's solution to this problem was to arrange other mass within the engine to be accelerating in the opposite direction such that the reactive forces were opposing each other - they ran the clutch and alternator jackshaft in the reverse direction via gears. Given the polar moment of these parts was approximately equal to that of the crankshaft the net result was no discernable rock to one side when the engine was revved.
They did have a big problem with another torque reaction however. Once testing began, the team found that the prototype Vee Six - with its short swingarm and single underslung rear shock absorber - suffered very badly from the tendency for the rear end to rise under power and squat on a trailing throttle. Once again, this effect was present on contemporary BMW and Guzzi machines, but with their modest power output and touring application this was not considered a problem. However with the Vee Six pushing out so much power the bike was - in Massimo's own words to me - "unrideable".
Following the theme of equal and opposite forces, a shaft drive arrangement on a motorcycle applies a certain amount of torque to the wheel through a bevel gear. For the wheel to actually turn there must be an equal and opposite torque holding the rear bevel gear housing (the "diff") from rotating backwards. Normally with an old-style Guzzi or BMW - and the V6 prototype - this is achieved with a 'torque tube'. The housing that encloses the shaft holds the diff housing from rotating and transmits this force into the frame through the pivot point.
Laverda's solution was to construct a much longer swingarm, pivoting near the clutch housing - the bikes measured centre of mass. Unlike the arrangements more recently used by BMW and Guzzi where the housing floats, held in place by a parallelogram linkage, the V6 "diff" housing was still fixed to the swingarm. Laverda's long swingarm achieved the result by different means; firstly its length reduced the resultant force at the pivot point, and secondly it applied that force to the chassis at it's centre of mass, therefore did not 'rock' the bike fore and aft. The downside of this system was that the radically different lengths of the swingarm and shaft meant the load on the transmission joints were increased. At the time there was no joint that could take the high speed and load along with the angular range required by the swingarm setup.
During testing at the Mugello circuit the bike showed significant improvement from the prototype's unruly behavior. It was by no means finished, but had taken some major steps in the right direction and with that the team prepared for its competition debut at the Bol'd'or 24 hours endurance race of 1978. The driveshaft had not been conclusively tested however there can be no test more extreme than a 24hr endurance race.