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Author Topic: Putting hit and miss engines to work. A guide for the total novice.  (Read 88 times)

Adirondack Jack

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If you’re an old hand with the arcane stationary engine and it’s use, I am probably not writing for you. But if you’re a new owner, likely with one of the amazing and affordable Chinese made hit and miss engines, and want to put it to work, I’m here to report what I’ve learned on my novice journey.

So you got your engine started and It’s running well. You’ve read all about fuel and mix oil, lube oil, and have a pretty good handle on the care and feeding of your little boominstinker.   Now it’s just begging for a job.  What can it do? What do you need to make it happen? What kinds of issues are you going to have to concern yourself with?

Let’s start by following my journey with my first and to date only hit and miss, the Eachine M91 vertical hit and miss.

Once I got it running, I dreamed of creating a miniature woodworking shop, with a working lathe, drill press, maybe a bandsaw, all running off a line shaft system.

The first issue was how to figure out what the engine was capable of. It’s not like a Briggs and Stratton where you can just look at the spec sheet and build a go cart based on the eight horse horizontal shaft engine.
Nope. You have an homage to an antique, in no particular scale, and unknown power output. Forget whatever you know about high speed engines. This puppy makes its power at lower rpm levels than the average lawnmower will reliably idle. It’s all about those big heavy flywheels and momentum creating torque at low speed. You can run substantial loads if you use the right “gear ratio” (pulley sizes) to get the speed and power required.

So I built a simple line shaft system first. That taught me about plain wooden pulleys and quasi flat belts. Unlike v or round belts, flat belts run on crowned or tapered pulleys with no rims to keep them on. So you’ve got a touchy alignment issue to keep everything happy. With a short belt, the smallest angular misalignment can spell trouble.  Longer belts are a bit more forgiving, but the sweet spot where they’ll run without running off the pulley still isn’t all that wide. Think about shaft play in your bearings, control of shaft flexing under tension, and pulley alignment. 

Enter the “engine sled”.   I’d ditched the original engine stand in favor of a longer, lower, wider, and heavier running stand made out of hard maple   Now I needed a way to keep the engine and the line shaft system aligned while running, and to allow easy and repeatable belt engagement when throwing it in or out of gear.
The sled is just that. It’s a rectangular tray built to allow the engine to slide perpendicular to the crankshaft, with a latch to hold the engine in place with the belt engaged.

I’d already envisioned multiple appliances to run off the engine, so the sled is kinda generic, with interconnecting “docking pieces” made to fit whatever machine I might run independently, or to dock up to the line shaft.

The interconnect for the line shaft is mounted along the outside edge of the “workshop floor” so the engine is parked outside and engaged to run the line.  Once I’d run the line shaft naked, with no machines, I did some hillbilly dyno testing, consisting of squeezing the main line shaft hard with a leather gloved hand, trying to slow or stall it. The power of the shaft running approximately 250 rpms was impressive.  It was impressive enough to embolden me to build a piston water pump to use for further load tests. I wasn’t about to build an entire workshop until I’d put a bit more proof in the pudding.

So I built a piston type water pump that runs off a belt drive reducing its speed to just about sixty rpms. It’s a long stroke, small diameter, 3/8x2 inch pump, running off a long, 3.5 inch center to center connecting rod and an external wrist pin. Everything except the rod small end is all on 5mm shaft with ball bearings.  With the pulley and belt system in place, it takes very little effort to drive the pump by turning the intermediate shaft that will be driven by the engine.

Today I finally finished my interconnect docking piece to secure the engine sled to the pump, and ran the pump off the engine for the first time. The interconnect is two pieces, with a slotted adjustment to allow fine tuning lateral alignment, with a single 3mm screw to secure the two parts in position.
It pumps like crazy, only drips about a drop a minute around the piston seal, and yes, by golly, the 6x1.5 mm timing belt I’m using as a reasonable approximation of flat belts stayed on their pulleys.

The procedure to get it going is like this.

Latch the engine sled and interconnect dock to the pump base. Place the engine in the sled. Do not put the power belt on the engine.  Start the engine, run it a minute or three to warm it up. When it’s running happily, shut it off with the battery switch.
Now the trick part. Wind the starter cord around the starter pulley and let it hang free.  Install the drive belt loosely, with just enough slack so the engine freely slips instead of driving the pump or other appliance.  Switch the power on and start the engine. Let it stabilize a few seconds, then slowly slide the engine in its sled until the belt engages, and the engine slide latch drops into place   If your sled interconnect is adjusted properly so the pulleys are correctly aligned, you can repeat this process blindfolded and it’ll work. If not, you got alignment issues to work out.
Meanwhile, I’m happy to report this pump is nowhere near overloading the engine, and I got me the baddest steampunk squirt gun ever.  Im also confident enough that I’ve conquered the “how to put my engine to work” issues, to go ahead and build machines.

It’s all about controlling the alignment of the engine and appliance, and using the right belt and pulley ratios yo get reasonable speeds. This engine wouldn’t pump water at 1000 rpms, even if the pump stayed together. That would simply require more power than it makes.  But reduce the pump speed to sixty rpms, it’s plenty.
Pics are pretty self explanatory, or ask. I’m off to build a wood lathe. 


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