300 Hp Miller Improved Gas Engine at Coolspring Power Museum 

It is actually a flat engine not a boxer. They are different. Boxer has one crank throw per piston. Flat has one crank throw for two pistons.

The engine has 1 50(?) foot long piston rod, with 2 double faced pistons on it. ie, the pistons and cylinders are each like a steam engine cylinder. The 2 cylinders are sealed at both ends, resulting in 4 combustion chambers. At the flywheel end is a relatively short conn rod to the crank. Since it's a 4 stroke, it takes 720 degrees to fire both ends of both cylinders. Watching the camshaft, you can see the 4 firing events, at 0 degrees, 180, 360, and 540 degrees. Of course the piston rod has joints in it, to allow getting the pistons in + out for service.

@@SteamCrane thank you for the explanation. It finally makes sense. I wonder if that Snow engine was made by an earlier steam engine manufacturing company.

@@Raj-nh3fc Yes, Snow Steam Pump Works, Buffalo NY. The steam version would have had only 1 double acting cylinder. There are videos on YT of big horizontal steam engines with the same camshaft driven valve gear. BTW, notice the adjustable links above the cylinders, to allow individually adjusting valve operation for each end, controlled by the governor. Coolspring had hats made up with a very well made embroidered Snow Steam Pump Works nameplate. I have several of them in various states of wear.

@@SteamCrane thank you again for the information. I am beginning to realise how closely the steam engine and horizontal gas engine are related. The steam engine technology filtering down to horizontal gas engine. I even saw a YT video of a rice mill steam engine in Thailand where the owner had used the crankshaft and fly wheel of a Ruston crude oil engine mated to a cylinder and piston of a steam engine, a hybrid. It was a steam engine fired by rice husk.

@@Raj-nh3fc There are a lot of videos of steam powered rice and sugar cane mills on YT. Search for "Join the Industrial Revolution!!! Gula Java 12, Gondang Baru, Central Java, Indonesia", a full hour showing a row of big stationary steam engines powering a sugar cane mill. The engines are all different designs, different valve gear, and one is a twin. Steam is provided by burning the bagasse, what's left of the sugar cane after the sugar is removed. Thus their fuel cost is zero, as is their cost of disposing of the waste stalks.

It is a 4 stroke, thus there is a power event on every half revolution. A different configuration to get the same uniform power flow as the Snow.

so while one cylinder is in exhausting fumes the one next to it is in it's compression cycle? that makes more sense, so the camshaft runs between the cylinders and the towers we see on the side of the cylinders are valves? I'm always eager to learn about old equipment. Thank you!

"This engine is known as a Model 3 Open, which is descriptive of its size and layout. It features a quad-opposed style in the “H” design with one center flywheel."

The most accurate means is a Prony Brake. This is a drum like a flywheel, with a brake band around it. There is water running to cool the drum, and some lard to keep it from seizing. The brake drum is mounted so it can rotate a bit, and a lever arm sticks out radially. The lever arm pushes down on a balance beam scale. Measure the weight on the scale at a known radius and you get foot pounds torque. If you can measure RPM, this gives horsepower very accurately. I have several Prony Brake videos up.

It was built in 1913, so it's 104 years old now.

We own several ~100 year old engines, although smaller. Run great. They were built to last.

4993.56 ci

Yes, 4 cylinders. 2 sets of opposed cylinders. The cranks on each side are in time, so the pistons on opposite sides move back + forth together. You can watch the valves on each cylinder moving to see the firing order. Close up, it's one of the most insane engines you'll ever meet.