PM Research Model 3 Steam Engine
This is a PM Research model 3, a horizontal mill engine. Specifically, it's a model 3BIM, meaning the machined bronze and iron kit. PM Research is one of the few companies that offer machined kits, which is great for people like me with no machining equipment or know-how.
Here's what was in the box: the base, flywheel, cylinder, a bag of parts and a bag of hardware.
Portions of the plans. This single sheet is all that's provided in the way of instructions. Additionally, I went to the web site of Graham Industries and downloaded their instruction manuals. The Graham manuals are more elaborate and contain some general tips and information that can be applied to the assembly of other engines like the PM Research models.
Some of the parts spread out.
All the casting surfaces that are necessary for the engine to run are machined. So I could have just slapped it together and it would have worked, but it would have been ugly. Some filing, polishing and painting were in order. I loosely put some of the parts together just to see how it would look. The picture shows how rough looking the connecting rod was. A lot of the parts were like that. The plan is for a red, black and polished bronze color scheme.
Here's the base, now gloss black. The far crosshead cap is untouched. The near one I worked with a conical stone in my Dremel. Next I'll switch to a polishing bit and some polish. After a morning of masking, other bronze parts were pained red. I just used Rust-oleum rattle cans. The parts didn't take the red paint as well as I had hoped. It came out okay, but I should have taken the time to prime the parts.
Here's another test fit after painting. The chrome hardware is intolerable.
This picture shows the valve, eccentric rod, eccentric, eccentric hub, piston, piston rod, crosshead, connecting rod, crank and crank shaft.
And here's all that on the base minus the crosshead caps and flywheel.
The piston without the cylinder. Note the two Teflon piston rings. I put some Loctite on the piston nut.
Here's my test rig for hooking up a compressor to the engine. The gage assembly has a built-in ball valve.
The first test run took 25 pounds of air to get going. I set the eccentric hub at -90 degrees relative to the crank. Thus the engine is set for "running under" or clockwise, which is the common direction for this engine type. Running under cause a continuous down pressure on the crosshead. So far, no wear at all is evident on the crosshead caps. But it still needed some adjusting and breaking in. I had to polish off some of the paint on the connecting rod around the crank bearing. It was too tight. The motion of the connecting rod kept unscrewing the crank bearing and it would fall apart. I'll Loctite the bearing screw after I make sure everything else is working well. Also the valve was binding a bit. As you can see in the pictures, the eccentric rod needs to be bent in an "s" shape because the valve is a bit offset from the eccentric. Bending the rod was the most difficult adjustment to get right.
After the first hour of wear, I was able to keep engine clunking along at only 4 psi. But the piston is still a little tight at top dead center. I think the lower crosshead guides machined into the base are ever so slightly too high relative to the cylinder. This is causing friction between the piston rod and the packing nut. I'm thinking the problem will go away after the crosshead is worn in. Also, the lubricating oil is peeling the red paint off the eccentric hub. Just painting wasn't good enough. It needs to be stripped, scuffed with sand paper, primed and repainted. And as suggested in the instructions, I still need to seal the valve port set screws and the intake and exhaust pipes. As a final touch, I added some "O" scale mechanics and I replaced all the chrome screws with black socket head cap screws. The end result is shown at the top of the page.