Vincent Rotary

A cylindrical Triple from the father of the frameless British V-Twin.

Three cylinder rotary diagram.

Composite section view of the crankshaft in Vincent's three cylinder rotary.

We all know that Phil Vincent and his lead engineer, Phil Irving, designed one of the most influential motorcycles of all time: the 61-cubic-inch Vincent V-Twin. This machine was made light, compact and unusually powerful by a variety of techniques that continue to be employed today.

Very few, however, know that Vincent, after the demise of his motorcycle manufacturing business, addressed what he considered to be the outstanding problems of conventional piston engines in a compact three-cylinder rotary with peripheral valves much like those used in high-performance Wankels. Because he was able to raise only very limited backing for his project, Vincent forced it into being by sheer strength of character. Thanks to the generosity of former racer and Cycle World staffer Jody Nicholas, I was lent some of Vincent's papers and drawings regarding this project.

The cylinder block, containing three 54mm-bore radial cylinders and pistons moving through 18mm strokes, revolved within and sealed against the inside surface of a cylindrical outer ring. Passing through the ring were large intake and exhaust ports. Two sparkplugs were also threaded into it. Both two-stroke and four-stroke versions were contemplated. Valving was accomplished in both cases by the sliding of the open outer ends of the 120-degree-spaced cylinders past intake and exhaust ports in the outer ring.

Drawings for the Vincent Rotary Engine.

Vincent Rotary Engine Diagram.

To learn more, I got in touch with Big Sid Biberman, a wizard of Vincent tune and a Keeper of the Lore. He said that, unfortunately, the 1961-71 project had generated little more than oily smoke and disappointment.

Vincent well knew that attempts to make high power from conventional engines ran up against limited valve area, valve float and mechanical stress. His rotary sought to provide very large ports unobstructed by rpm-limited mechanical valves. He could see no reason, thanks to his complex hydraulic sealing system, why it should not operate at extreme rpm.

This seemed achievable, I suspect, because Wankel prototypes had, not long before, overcome similar sliding-seal problems to run and make useful power. The leakage and smoking of the Vincent rotary probably resulted from heat distortion of the outer ring around its hot exhaust ports.

Sealing surface distortion around the exhaust ports of two-stroke Grand Prix-bike cylinders in the 1990s was overcome only after development of complex cylinder-shaping technologies. Vincent lacked the resources of a major R&D department to sort out his engine’s problems, so, it came to nothing. The prototype and many of his engineering drawings have been preserved.

Three cylinder rotary diagram.

Composite section view of the crankshaft in Vincent's three cylinder rotary.

Drawings for the Vincent Rotary Engine.

Vincent Rotary Engine Diagram.