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| Conversion of 4 Cycle Utility Engine to Steam |
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| vtsteam:
So that brings us up to the present I have a new idea. :smart: Uh, external crankshaft mounted eccentric driving a valve in a new head casting. Well maybe not so new. Been around for at least a century or two. |
| vtsteam:
Actually, external valve gear had been my original plan before I started searching around the web for conversions other people had made. The internal camshaft modifications seemed to be the most common, and promised a quick and simple conversion. It certainly would have been nice to package everything inside the engine by modifying a camshaft. And these modifications are certainly do-able, elegant, and probably fun. But they don't result in an efficient steam engine, or one with much power output. Well I should modify that statement -- if there is clearance for sufficient sized cam lobes on a half speed camshaft, then it would be possible to get good timing figures. But on the Tecumseh, at least, it isn't possible. My main interest are the Westinghouse style twin engines, like the Stuart Turner Sun and Sirius, and other model boat engines built in the early history of model steam boat racing. I own two antique model Westinghouse style engines, and once started construction on a new one. Westinghouse twins almost always have external valve gear (though there are exceptions) and something similar to this for valve actuation was what I had originally imagined for the Tecumseh single conversion. That conversion was intended to give me practice and performance figures for a subsequent scratch built Westinghouse style twin. Well, now it's back to that original idea, external valve gear and a head casting to receive the valve. My plan now is to try a shaft type rocking valve coupled to an eccentric on the crankshaft. This seems to me to give a very simple linkage, allowing me to use pressure to keep the valve faces steam tight, as well as compensate for wear, while reducing wear over a full rotary valve. A piston valve could also be used, but these must be very well fitted, and it seems to me that any wear, no matter how well fitted originally, would lead to steam leaks. Traditionally, a D-valve was used on top of the head, with a linkage composed of either bevel gears and a vertical crank shaft, or a long bell crank and a ball end somewhere in the linkage to take up side motion. I think my choice is the simplest I can think of for linkage, and offers some of the advantages of all of the other valve types. So, on with the show...... |
| vtsteam:
I had a little time today to work on the head pattern. Here it is being tried on top of the cylinder. |
| DavidF:
Looking good, not 100% sure what your up to yet but judging by the bosses in the side of the head it should be interesting. |
| vtsteam:
Hi David. The bosses on the side of the head will form the valve housing. The bosses will be bored through the head to fit the valve. The valve itself will be a shaft which rocks, driven by the eccentric on the crankshaft directly below those bosses. A pushrod will connect the eccentric and a horn on the valve shaft. The shaft will have milled areas to pass steam to and from the cylinder head beneath. The long oval boss on top of the head will be drilled and tapped for a steam inlet pipe and an exhaust pipe. Two ports directly under these, below the valve body, will be the steam in and exhaust ports. It's all very simple. |
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