In the early days of gas engine manufacturing, engineers were constantly testing ideas to make gas engines easier and more reliable to operate. Working for Alma Mfg. Co., Alma, Michigan, engineer Walter J. McVicker came up with a novel means of controlling exhaust valve and ignition operation for what became known as the McVicker Automatic Gas & Gasoline Engine, which was produced by Alma for about 10 years starting in 1903.
Instead of gears timing the crankshaft and valve operation, McVicker developed a ported system that used pressure created by the moving piston to charge an auxiliary valve that actuated the exhaust valve. In the McVicker Automatic, as the piston moved rearward following combustion it uncovered a port in the cylinder. Pressurized gas from combustion pushed into the port where it was channelled to open a small, spring-loaded valve. As the valve opened the pressurized gas fed into a second channel, where it pushed against a small auxiliary piston (“J” in the drawing). The piston’s stem rested against the exhaust rocker arm. As pressure moved the piston, the piston pushed the rocker arm, holding the exhaust valve open until the combustion piston reached the end of its stroke, at which point it uncovered a second port to release the pressure acting on the valve actuating piston.
Ignition voltage was controlled by a swipe on the crankshaft. A collar on the crankshaft had a contact face, with the circuit completed by a secondary contact that was fixed to the flywheel, rotating around and outside the collar on the crankshaft. As that contact brushed past the contact face on the collar, the ignition circuit was completed. Governing was by an adjustable weight on the flywheel contact, pulling the contact away and interrupting ignition at engine speeds above a desired setting. The exhaust valve stayed closed on the over-run, the piston recompressing the charge. Timing could be adjusted by rotating the collar on the crankshaft.
Contemporary Alma ads trumpeted the McVicker Automatic for having “one third the number of parts” compared to a standard engine and for being “the only four cycle engine that will run either way,” which, in fact, it could, thanks to its gearless operation and simplified governing.
Early tank-cooled engines followed the original design as spelled out here, with later hopper-cooled engines following an updated design specified in patent number 887,502, granted in 1908. This new design shifted the role of the auxiliary “automatic” valve actuating piston. Instead of pushing against the exhaust rocker arm, it now controlled an eccentric-driven pushrod, lifting the pushrod up and in line with the exhaust valve stem during regular operation and dropping the pushrod out during the over-run.
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