QJMotor’s Unusual Supermono Engine

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QJMotor has filed patents for a single-cylinder engine that utilizes a second dummy cylinder as a counterbalancer. (QJMotor/)

We normally define an engine by its number of cylinders: Singles, twins, triples, and fours are all commonplace. However, a new design by China’s QJMotor throws those definitions into chaos, as it has only one “active” cylinder, but it’s also a V-twin with a second cylinder and piston used purely as a counterbalancer.

The idea of converting a V-twin into a single isn’t new. Ducati famously created its 1990s Supermono racer by lopping the rear cylinder from its Desmoquattro V-twin. The Italian company stuck with the V-twin crankshaft and even kept the rear connecting rod, attaching it to a weighted rocking linkage that replicated the mass of the missing rear piston and gave the engine the balance it needed to rev higher and make more power.

Related: Suzuki’s Supermono Engine Design

Here you can see what Ducati’s solution to the same idea was. It called the design “Doppia Bielleta.” (Cycle World Archives/)

During the Supermono’s development, Ducati considered keeping the rear cylinder and simply deactivating it by removing the cylinder head but decided that the additional friction of a spare piston moving in the bore would sap too much power. The final design turned out to reduce friction and made for a more compact engine. Now China’s QJMotor is exploring the original idea, filing patent applications for a single that has a second, inactive cylinder and piston mounted at 90 degrees to the main one.

A look at the crankshaft and a pair of connecting rods to which are attached a traditional piston on one journal and a dummy piston that is actually a counterweight with a hole in it so it won’t compress the air. (QJMotor/)

But this isn’t just a V-twin with the rear cylinder head removed. In QJMotor’s designs, the second cylinder has a much smaller bore than the active one, with a weighted piston that’s designed specifically as a balancer. The piston itself has a large hole in its middle so it’s not unnecessarily compressing air, and the inactive rear cylinder is cast in a single piece with its head to keep the engine sealed.

Related: Motorcycle Engine Balancing Act

Ducati’s Supermono appeared on the pages of Cycle World in the September 1993 issue. (Cycle World Archives/)

The benefit is the same as with the Ducati Supermono, as the engine’s balance is the same as a 90-degree V-twin, without the addition of balance shafts or other weights. QJMotor’s patent specifically says that the engine is intended to be used in motorcycles but doesn’t reveal its capacity or what sort of bike it’s intended to be used in. Whether it turns out to be a clever solution or an engineering dead end remains to be seen, but if nothing else the patent shows that China’s motorcycle industry, with its reputation for copying rather than innovating, is expanding its R&D capabilities.

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