1895 Mery Explosive

A Double-Acting Six-Cycle Wonder/ the Mery Explosive Marks a Unique Page in Engine Development


| November/December 2002



1895 Mery Engine

The Mery as found by Bob Patty and photographed by Ken Beat sometime in the early 1970s. Note the spark plug fitted to the front of the forward cylinder in an attempt by Bob to get the Mery running.

"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 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.' That Mery's engine was (and indeed still is) unique in design is obvious. 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. The Mery utilizes a crosshead with a connecting rod running forward and into the rear cylinder and an additional 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 here 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. Originally igniter equipped, the Mery utilized its own governing system that combined speed governing with hit-and-miss load control. A fly ball governor controlled intake valve operation to govern engine speed, and a pendulum operating on the exhaust linkage raised a lever to catch and hold the exhaust valves open, providing the engine's hit-and-miss feature.

But the Mery's unique design doesn't stop there, for this is, after all, a double-acting engine. What this means is that an explosive charge acts 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. What makes the Mery work is its six-cycle design, wherein a 'purge' valve incorporated into the bottom of the exhaust manifold alternately pulls fresh air into the exhaust manifold and then clears it out, effectively limiting exhaust gases from drawing back into either cylinder and in the process keeping the cylinders cool. A very unique engine, indeed.

Surviving Merys

Up until a few months ago it was thought only one Mery Explosive Engine from the Chico Iron Works of Chico, Calif., existed, that being the circa 1895 4 HP Mery belonging to Chuck and Peggy Schoppe, Los Gatos, Calif. The Schoppes' Mery is well known on the West Coast, the Schoppes taking it to numerous engine shows over the years, most recently the EDGE&TA show in Grass Valley, Calif., this past June. The Grass Valley show was my first introduction to the Mery, and its construction and design intrigued me. I am not alone in this regard.

Roland Morrison, Benton City, Wash., first saw the Schoppe Mery (as it's commonly called) in 1982, and to say he was taken by the Mery is a bit of an understatement. Roland, who designs and builds scale engines, eventually took on the challenge of crafting a working 1/4-scale of the Mery engine. After years spent studying every detail of the Mery's design, it's doubtful anyone alive knows more about how the Mery works than Roland. In 1998, after five years of working out pattern details with pattern maker Gary Martin, and after working through the myriad problems of scaling down the unique mechanical attributes of the Mery, Roland's Mery became commercially available. An incredibly exacting scale replica, Roland has sold around 100 patterns kits, and there are now a few dozen scale Merys running. This has clearly been a labor of love. 'We never figured there would be a profit, and we have yet to break even,' Roland says of the venture.