Last time, I described the design and construction of the cylinder and crankcase for the steam engine. This time, I'll be wrapping up the basic design with the cylinder head and cam drive. Without getting into too much detail (I may yet try to patent this thing), the valve alternately allows steam into the cylinder and vents it out again during the upstroke.
Combined with the cylinder exhaust ports, this configuration is referred to as a semi-uniflow engine. If I did not vent the upstroke and allowed it to recompress, which would maintain the temperature gradient of hotter at the top and lower at the bottom, then it would be a true uniflow engine.
I felt, however, that the loss of thermodynamic efficiency was acceptable if it reduced the risk of hydro-locking the engine (where a liquid, which is basically incompressible, enters the cylinder and stalls it with potentially damaging results). I would rather have it work with a high degree of reliability than be highly efficient, but prone to breakdowns.
The Cylinder Head
The cylinder head was the most difficult part of the engine to design, and went through multiple revisions until I was satisfied with the result. Yet the first design still failed miserably, which prompted further redesigns. All told, I spent at least a month just sketching different configurations before I came up with one robust enough to work (although it was much more difficult to machine). It would be another four months until I came up with a design that was both robust AND simple to make, but I will discuss that during a later installment.
The Cam Drive
The final part to build for the motor was the cam drive. Given my lack of money and the large number of abandoned bicycles on campus, I was able to repurpose two of the rear sprockets from a cannibalized 18-speed. As luck would have it, the largest and smallest sprockets on the rear wheel were a perfect 2:1 ratio. I made up some adapters to attach the two, cut an old chain to length, and finished assembling and timing the engine. (Note: I do not recommend doing this for a cam drive. It is insanely dangerous and WILL take a finger off if you get caught).
Amazingly, the motor ran under its own power on compressed air after only 15 minutes of fiddling. After testing it and making sure it worked, the next step was to build a test stand.
Follow this link to see the motor in action.
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