Gas Engine Magazine

1895 Mery Explosive

By Staff

“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.

When Roland saw the Mery for that first time in 1982 it belonged Bob Patty. Bob, a Chico, Calif., area engine collector, bought the Mery from a scrap dealer in nearby Orland sometime in the 1960s. Bob evidently played around with the Mery, trying unsuccessfully to get it running. According to Ken Beal, Chico, Calif., Bob threaded an additional spark plug into the face of the forward cylinder in a bid to give the engine some extra spark. He also tried starting it with a tractor. ‘Bob had an old Case, and he tried turning the Mery over belted to that, but it just wouldn’t run,’ Ken says. Sometime around 1972 Ken, after meeting Bob and seeing the engine, took the Mery home to see if he could sort it out. By the next weekend Ken had the Mery running.

The Mery was missing (and still is) its original governing mechanisms, but by fitting up a Maximus timer from a Ford Model T and using two of its four terminals, Ken got the Mery to start. ‘It really didn’t take much, just figuring out the timing,’ Ken says. Ken and Bob deduced the Mery’s six-cycle design by looking at the Mery’s timing gears. The Mery has a crank gear with 51 teeth and a timing gear with 153 teeth, resulting in a three-to-one ratio.

Up to this time Bob didn’t know what kind of engine he had, and it was Ken who conducted early research at UC Davis in Sacramento, Calif., discovering papers in the University’s library that shed the first light on the engine’s origin.

After Ken got the Mery running it was painted green with yellow accents. ‘Right above the front of the crosshead there was a lot of grease,’ Ken says, ‘and I cleaned that off and there was green paint and a wide, yellow stripe.’ Some time around 1977 the Mery was damaged when Bob pulled short into a parking area and the Mery hit a concrete barrier. The Mery broke at the crosshead, and after it was repaired Bob painted it red, the color it wears today.

Bob Patty died in 1986, and a few years after his death the Schoppe’s bought the Mery from Bob’s estate. According to Chuck and Peggy, they were actually the low bidders on the Mery, but it was sold to them because of their promise to keep it in the area and to show it regularly. The Schoppes have lived up to their word, showing the Mery regularly and keeping it in good running order. They have equipped the Mery with a custom-made screen cooler, replaced all the ignition lines with period-style cloth-covered wire and fitted a different propane system to it than the one Bob used. Using newly machined parts made by Francis Tarzian, Chuck rebuilt the timer, and some good luck joined the Mery with the nickel-iron Edison cell battery array it runs on today.

Another Mery Surfaces

The Schoppe Mery was thought to be the sole surviving engine. At one time Bob Patty supposedly had a picture of a two-cylinder vertical Mery, and a occasionally there were hints that another Mery might exist. Those hints, it turns out, were true.

In the summer of 2000 Don and Judie Decker, Ridgecrest, Calif., pulled a Mery engine out of the wild, found not 30 miles from where it was built over 100 years ago. According to Don, who says he never would have succeeded in finding the engine without Judie’s help, it took ‘perseverance, sleuthing, negotiating, horse-trading and dealing with mosquito clouds from hell’ on both his and Judie’s part to track down and acquire the Mery.

Mery Number 2, as it is being called, appears to be a later engine than the Schoppe Mery. There’s no proof to support this contention, but differences in the two engines support the theory. For one, Mery Number 2 features a prominent rib under the crosshead guide to stiffen and strengthen it. If you’ll remember, this is where Bob Patty’s Mery broke. The crosshead itself is different, featuring an easily set adjustment to take up wear in the babbitt-lined crosshead. Mery Number 2 also has small changes to the gussets in the main bearing area. Additionally, Don’s engine has a round belt pulley on the intake side of the engine outboard of the flywheel that used to spin the flyball governor. This same pulley is on the Schoppe Mery, but mounted on the exhaust side and sandwiched between the crankshaft pinion gear and the flatbelt pulley. Don believes the pulley was removed at some point from the Schoppe Mery and inadvertently installed on the wrong side when the engine was stripped of its governing devices. Like the Schoppe Mery, there are no numbers on Mery Number 2.

Studying parts of the engine, Don believes it was used regularly in its earlier life. ‘It’s telling you it functioned for a substantial period of time,’ Don says of the Mery’s condition. Don says there’s a chance this engine was originally employed pumping water outside of Chico, noting a rumor of a Mery supposedly taken from a pump house that was scrapped in the 1950s. Don says that rumor’s chronology fits with the circumstances of Mery Number 2 and its location when found.

Don says he’s spent some 800 hours researching the Mery, his ultimate goal being the compilation of a complete set of drawings so he can have parts manufactured. Don would like to bring his engine up to running condition and also supply parts that are currently missing on the Schoppe Mery. ‘It’s a sufficiently unusual engine,’ Don says in describing his pursuit, ‘and the Schoppe is sufficiently incomplete.’

More Merys to Come?

We don’t know how many engines the Chico Iron Works made. It’s possible it was only a very few, and clearly not too many could have been made or there would be more surviving examples. Why both surviving Mery engines are missing their governing devices is a curious point, raising a question of whether Mery’s governing devices worked as planned – it’s entirely possible they functioned poorly in actual operation. Roland has worked out drawings for the Mery’s governing system, and some model makers have experimented with building them. If Don has his way, someday a full-size Mery will run as originally drawn out and built by Michael Mery over 100 years ago.

The Schoppes are currently compiling a history of Michael Mery and the Chico Iron Works, and Don Decker and Roland Morrison continue to collect technical information on the Mery engine. The last chapter of the Mery engine has yet to be written, and with a little luck, and a little time, we’ll all have the opportunity to be there when it’s finally done.

‘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.’

Special thanks to Chuck and Peggy Schoppe (, Los Gatos, CA, Roland Morrison (, Benton City, WA, and Don Decker (, Ridgecrest, CA, for their invaluable help in supplying previously unseen photographs and technical information. Anyone with information on Mery engines is encouraged to contact them at the e-mails listed above.

  • Published on Nov 1, 2002
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