The Wooler engineTags : con-rods
We motorsport engineers are a lucky bunch; I tell people that, as an engineer, there are few areas of the engineering industry that can approach the rewards of Formula One in terms of the scope for creativity and the willingness of companies to explore new ideas. For many years, when the regulations governing motor racing were more liberal than they are now, we saw some incredible innovations, and a fair share of them came from the motorcycle fraternity. The incredible Honda NR engines, with their four ‘oval’ pistons, 32 poppet valves and eight con rods remain unique – not only has no-one else attempted to do anything similar, but Honda itself have never resurrected the idea. It did persist long enough though to make a very expensive road bike, examples of which now change hands for a great deal of money.
Another four-cylinder motorcycle engine, although not a race engine, also had an unusual number of con rods to control its pistons. The Wooler had a single-throw crankshaft, a single primary con rod and four secondary con rods, although the primary rod was not actually connected directly to the pistons. Whether we consider this engine to have one con rod or five, it is certainly a novel concept. Fig. 1 shows an actual Wooler engine while Fig. 2 is a cutaway drawing of it.
The primary con rod, connected to the crankshaft, actuates a lever, causing the actuation point to move back and forth along an arc. The lever is connected to a further lever to which four secondary rods are attached, which move the pistons back and forth in the bores. The pistons are arranged in pairs above each other, with two opposing banks of cylinders. The engine was arranged with the cylinders on each bank above each other and these cylinders above the crankshaft, making the engine pretty tall. The images here show the layout of the engine, which is difficult to describe with words alone. The lubrication of the cranktrain would be problematic, as only the crankshaft end of the primary rod is in constant motion – the remaining pivot points would all experience intermittent motion.
The Wooler’s cranktrain is a complex mechanism, and is perhaps not a pretty packaging concept. The connection between crankshaft and pistons is not very stiff, and there are more moving components than are strictly necessary. All of this means we are unlikely to see anything like the 1950s Wooler 500 cc motorcycle return to the roads, and we can be almost certain that we won’t see its like on a racetrack.
However, as an unusual mechanism and use of con rods, it has been worthy of this brief examination. It seems to be a complex solution to a problem that didn't exist: there were a number of four-cylinder motorcycle engines of the same capacity which worked perfectly well with more conventional layouts although, at the time, single- and two-cylinder motorcycles were definitely the norm for road bikes as well as many racing bikes.
Fig. 1 - The Wooler engine, showing the arrangement of the primary and secondary con rods
Fig. 2 - Cutaway drawing of the engine, revealing more details of the packaging of the other components
Written by Wayne Ward