Speed Demon Diesel


Name Speed Demon Designer unknown
Type Compression Ignition Capacity 0.296 cuin
Production run unknown Country of Origin under debate
Photo by Bert Striegler Year of manufacture unknown



This engine is almost a "Watzit", except we know watz it is; what we don't know is werez itz from! The "Speed Demon" was made either in Switzerland, France, or the USA. Construction is fully from bar-stock (no castings) and it features a rather unusual compression adjustment mechanism. The cylinder liner has a blind bore and slides up and down inside the aluminum jacket. The compression adjusting lever has a push/pull action (like modern T/R diesels)--the cylinder liner being prevented from rotating by a little pressed in peg (not visible in these outstanding photos). Notice the oversize (vertical) exhaust opening so that adjustment won't throttle the engine back (though what it's doing to the timing will be *wild*).

The engine pictured here is from Bert Striegler's collection. Bert took some measurements and found everything was Imperial and the threads are standard UNF, arguing for a US origin. However other evidence in the form of a letter accompanying a replacement needle valve assembly indicated European origin. The Swiss making an engine to Imperial dimensions? Perhaps. The French? Never! Bert's measurements show that the Speed Demon has the same bore and stroke as the Drone Diesel (21/32" x 7/8"). The pressed drive washer is, we believe, identical to that used on the Herkimer OK 29 and Bert thinks he remembers reading that the engine was made in New York (state) by a company who produced parts for Herkimer under contract and needed a new cash-flow generator following the Second World War. So, as they say... Watch This Space.

With every Motor Boy urging him to destroy, or at least intimately violate his priceless example, Bert pulled down the monster to record how it goes together. Fortunately, the only thing destroyed in the process were my theories on how it was built. Here's his report:

...I could not remove the shaft as they pressed in an overlength bushing into the rod to limit rod movement against the backplate, and I could not budge the bushing without probably destroying it.

The cylinder is dead simple. It is a straight piece of tubing with a 5/16" deep head pressed into the top. There is no sign of any mechanical fixture here, so it must simply be pressed in. After all, it is the head that takes all the combustion pressure. The head has a central hole that is 1/4" deep and drilled and tapped for a 10x32 bolt. A 1/16" dowel pin is pressed into the head to keep the cylinder located in the cylinder casing. The pressed in place head has a 1/8" thick flange where it sits on top of the cylinder and this flange is the same diameter as the OD of the cylinder. I am guessing that the locator dowel hole is drilled with the cylinder sitting in the casing, then the cylinder is removed and the pin is pressed into the head.

The bypass channel is in the front of the cylinder casing and is a milled channel cut with a 1/2" mill. The cylinder assy is exactly 3/4" OD and is 2" long.

The crankshaft is a massive affair, as is the rod. The crankpin is 7/32" and the wrist pin is 3/16". The steel rod has a massive look about it and the body of the rod is 7/32" diameter. Both ends of the rod are bronze bushed. The crankweb is a full 1/4 thick. The crankshaft is 3/8" diameter and the propshaft is 5/16". The crank bearing appears to be a stock oilite bearing, 3/8 bore and 1/"2 OD by 1-1/4" long.

The cylinder looks and feels like ordinary leaded steel and the long trunk piston is cast iron. The wrist pin is pressed into place.

The comp screw is threaded 10x32 below the flange where it contacts the bottom of the hole in the cylinder casing. Above the flange, the shaft is smooth and 1/4" OD. The comp lever is a 1/8 piece of good steel, threaded 5x40 on the end that goes into the ring around the top of the comp screw.

That is about it. Workmanship inside and out is extremely good. It was a quality piece of goods. One more thing, the finished diameter of the lower crankcase is 1-3/4" so this is no light weight engine. It weighs 12.38 OZ, or 351 gm. That is a big, heavy 5cc engine for a .296.

Removing the tank also disclosed a serial number stamped on the mounting plate" 1255, indicating at first glance that over a thousand were made. I doubt that. It has not been uncommon for manufacturers to start their numbering at 1000 to give the buyer a sense of confidence that they had a popular, mature product. In this case, it would not surprise me if the numbering scheme commenced at 1200!




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