Patent Page: Mery Explosive Engine

By Staff
article image
Courtesy of Gas Engine Magazine Staff

Top-down view of the cylinder in Michael Lawrence Mery’s 1895 patent for the Mery Explosive Engine. The double-acting engine featured two igniter/intake valve chests (D), one at each end of the cylinder. Fresh air drawn in via a purge valve (L3) cleared out the exhaust manifold and kept exhaust gases from drawing back into the cylinder.

“The object of my invention is to provide a double-acting explosive engine, simple in its construction of parts, efficient and accurate in its explosions, and capable of easy and perfect adjustment.”

So wrote Michael Lawrence Mery of Chico, California, in his patent application submitted Feb. 7, 1895. On July 23, a little more than four months later, Mery was awarded patent number 543,157 for his Mery Explosive Engine. Constructed in some measure along steam engine principles in common use at the time, the Mery is a double-acting engine featuring a single piston. Like a double-acting steam engine, the Mery utilizes a crosshead with a connecting rod running forward to a single cylinder and an another connecting rod running from the crosshead to the crankshaft. The connecting rod running into the cylinder passes through a water-cooled packing gland and then to the piston. But that’s where the Mery’s similarity to a steam engine, or any other engine, stops.

Its similarities to steam engine layout notwithstanding, the Mery is unlike any other engine in the annals of stationary engine design. Igniter fired, the Mery utilized its own governing system that combined speed-controlled volume governing with hit-and-miss load control. The intake valves were atmospheric and the exhaust valves were actuated by a rocking lever driven off the crankshaft. Another rocking lever, also driven off the crankshaft, actuated the igniters. To allow timing adjustment, the igniter rocking lever was mounted on an eccentric, which could be adjusted to alter the pivotal center of the rocking lever.

To control intake volume, bell crank levers acted upon by a governor engaged a stop on the intake valve stems, limiting the total stroke of the intake valves to control fuel/air volume. At their contact point with the valve stems, the bell cranks had graduated stops (see Fig. 5) to effect differing levels of valve opening. Below governed speed, the bell cranks were out of action and the intake valves were free to fully open. As the governor latched in, valve lift was impeded in steps, thereby limiting the amount of fuel/air drawn into the cylinders. For further fine tuning, the stops on the intake valve were adjustable.

On the exhaust side, a pendulum was mounted above the center point of the exhaust rocking lever. The pendulum rotated a disc fitted with two pins at roughly the 10 and 2 o’clock position (see Fig. 6). Resting on these two pins were levers running to the exhaust valve stems. As the pendulum swing increased with faster rocking lever action, e.g., engine speed, the pins on the disc would alternately lift the two levers, which at their ends were equipped with pawls to engage a shoulder on the exhaust valve stem to catch and hold the exhaust valves open, providing the engine’s hit-and-miss feature.

The intriguing nature of the design continues, for this was a double-acting engine, with an explosive charge acting on both ends of a common piston, pushing the piston and the connecting rod both forward and backward. Applied to a gas-powered engine this introduces some interesting issues, not least of which is the timing of intake and exhaust pulses. Central to Mery’s concept was the engine’s so-called “six-cycle” design (a term not used by Mery), with a purge valve incorporated into the bottom of the exhaust manifold to alternately pull fresh air into the exhaust manifold and then clear it out, effectively limiting exhaust gases from drawing back into either cylinder and in the process keeping the cylinders cool.

A very unique engine, certainly very few were built, as only two have been verified. One, restored by Chuck and Peggy Schoppe, has been in circulation at California engine shows for decades, regularly thrilling viewers. A second engine was located about 2000, but its current state is unknown. Such is the appeal of the Mery that it inspired scale gas engine constructor Roland Morrison to craft a complete set of castings to make running scale engines. The last time we checked, castings were still available at, with several scale Mery engines having been built over the years.

You can see one in action here.

Know of an interesting patent? Contact Gas Engine Magazine at 1503 SW 42nd St., Topeka, KS 66609-1265, or email

Gas Engine Magazine
Gas Engine Magazine
Preserving the History of Internal Combustion Engines