WYVERN Model Gas Engine


| December/January 1989



WYVERN Drawing

7574 So. 74 Street, Franklin, Wisconsin 53132

I never met a gas engine that I didn't like. Some I just like more than others, and this was one of them. Our hobby of building model engines really began in England, where model steam engines that were built in the 1700's exist in museums. At about the turn of the century, an English magazine called Model Engineer began publication. This magazine is still published today, twice each month, and bound volumes can be viewed in some of the larger libraries in the U.S. Plans for many steam, gas (petrol, as the English call it), and hot air engines have been published through the years in this magazine. One of the major designers of model gas engines was Edgar T. Westbury, whose works were always published in the Model Engineer. He designed racing engines, model boat engines, and this model stationary engine. He modeled the engine after a typical Crossley stationary engine, built in the late 1880's that was used to power machinery in English factories. While not an exact replica of a particular engine, it is representative of the engines of this period.

The model has the looks of a very early gas engine, with such interesting details as a side shaft to operate the two valve rockers, a counterweighted crankshaft, thin section flywheels, and turned (marine style) connecting rod. The engine has a 1.250' bore, by a 2.000' stroke, making this a long stroke engine. An early style head is used, again copied from a Crossley, called a 'clerestory' head, from the internal shape of the combustion chamber. The Crossley Brothers found that the shape of the combustion chamber, and the position of the valves, had an important bearing on efficiency. The clerestory head became popular at that time.

The WYVERN casting kit and drawings are available from Power Model Supply Company, Rt. 1, Box 177, N.W. Cor. Hwy. 67 & Long Road, DeSoto, Missouri 63020. The castings, made by Woking Precision Models in England (actually Scotland) are of very good quality. They are of iron, aluminum and bronze (called 'gun metal' in England). The drawings are clear and correct. A construction article, written by West-bury, and the drawings were published in The Model Engineer in 1963. This is available with the castings from Power Model Supply. Also included are the valve springs, the skew gears, two piston rings, and a 10 mm spark plug. I didn't use the spark plug provided because I prefer to use the smaller ?'-32 size plug, as it looks more in proportion on the model.

An aluminum cylinder head is provided. Here is a small problem. The intake valve is designed as a removable bronze housing that contains the valve seat. No problem here. But the exhaust valve seat is ground into the head. Aluminum will not hold up as a valve seat very well. There are two solutions to the problem. One is to make a removable bronze valve housing, with seat, for both the intake and the exhaust valves. The other is to get a cast iron head. This is the route that I took, although either way will work. A cast iron head for this engine is sold by Tom Alexander, Box 125, Iowa Falls, Iowa 50126. Tom also sells a different base for the engine, which has feet protruding from the lower rim, so that the engine can be anchored easily to a piece of wood or metal. The base provided does not have such, and therefore would be difficult to anchor to anything.

The crankshaft on my engine is a one-piece crank, with the two counterweights attached to the crank throws with socket head cap screws, counterbored into the weights. I believe in a one-piece crank for a gas engine as the surest way to be assured that the crank will stay together. The article calls for brazing a crankshaft from pieces. The choice is up to you, but I have found that it takes no longer to turn a crank from a solid bar, than to prepare the pieces, braze them together, and finish machine. And a solid crank is such a masterpiece, that the job has its own rewards in satisfaction.