Engine Design for Beginners:
The Schroeder Simple Single 049
Last update: Feb, 2007
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The Schroeder Simple Single appeared as a comprehensive construction series in SIC magazine, issues 49 through 54, 1996. The engine, which is based on the cheaply and (then) easily obtainable Cox 049 cylinder/piston assembly, can be built to run on either glow or compression ignition. The builder makes a bar-stock crankcase, crankshaft, venturi/needle valve assembly, and a rear rotor valve (RRV). Success is about as close as we can get to guaranteed in this life. Incidentally, the milled lugs on this example were my modification. Roger's design used a simple 3/4" square lump of bar-stock with lugs attached under the top bolts of the front and rear covers.
I totally agree with Roger's choice of RRV induction for a first project engine. It is simple to make compared to the reliance on the builders' skills at brazing required on a side-port design like the Victor, or correctly drilling a port in the crankshaft for a FRV design. The most complex operation on this engine is cutting the fine thread for the Cox cylinder. For a first engine project, a displacement of 049 cuin would be a bit on the small size if you are making the piston and liner, but in this case, that is not an issue. All the builder has to worry about is correctly turning a simple offset crankshaft and achieving a fit in the (unbushed) journal that is free, but does not bleed primary compression through a too loose fit. The seal of the rotor on the other hand is surprisingly easy to achieve, making this a truly simple engine to build and operate.
Bob Washburn, editor of SIC, tried to introduce a rating system for engine construction difficulty. This gave weighted numeric values to construction techniques involved like milling, brazing, castings verses bar-stock components, etc. All of these represent different skills required in construction. The sum of the categories was intended to give an indication of relative difficulty. That is fine, but one builder who has never cut a thread may be a master welder, so I find such ratings a bit artificial. Look at the plans. See what is required in relation to what you've done before, and don't be afraid to stretch a bit. Look also at the cost of making a mistake in the areas you are uncertain about. You could reject and scrap a dozen SSS crankcases with really feeling the material cost—though you'd get mighty sick of making them by the time number three came around.
If anything, the Simple Single was considered by some to be too simple. I've actually watched bystanders look at the Cox cylinder and sniff down their noses that if you didn't make everything, you haven't really made a motor. Generally, such snobs have never even tried. I think the Simple Single has a valid place for those with some combination of little time, little skill, and even less time to build the skill. But mindful that other builders would welcome more of a challenge, Roger came up with the Victor. This design may have moved the bar a bit far in the other direction and we'll examine it next. Proves yet again that you can't please everyone.
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