Patent Page: The First Overhead Cam Engine

By Staff
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courtesy of Gas Engine Magazine Staff
J.W. Raymond’s 1892 patent for an overhead cam gas engine.

Was this the world’s first overhead cam engine design? From the little we can find, it just may have been. Patented by engineer J.W. Raymond, San Francisco, California, in 1892, it preceded the overhead camshaft Springfield Model A, produced by Springfield Gas Engine Co., Springfield, Ohio, starting in 1895.

In Raymond’s design, the camshaft was mounted horizontally at the top of the cylinder head of the vertical engine and chain-driven off the crankshaft at one end. At the other end was a flyball governor to control engine speed.

The valves featured stepped stems; larger where they passed through the cylinder head and necked down where they passed through the “guide yoke” that also supported the camshaft. Springs between the yoke and the top of the stems supplied the necessary closing pressure, adjustable nuts at the top of the stems allowing adjustment. A second set of springs sat between the guide yoke and pushed against shouldered discs. These discs sat against the larger, shouldered part of the valve stem. As the camshaft spun, its cam lobes contacted the discs, pushing the valves open as the camshaft rotated. As the lobes rotated past the discs, the valves closed on spring tension. The purpose of the secondary springs was to hold the discs in mild tension to the shouldered stem to maintain contact, while also allowing the discs to ride up the stems in the event the engine was turned backward, ensuring no damage to the components.

Make-and-break ignition was achieved via a bevel gear on the camshaft that meshed with a matching bevel gear on a vertical shaft passing through the top of the cylinder head. At the end of the shaft was a lobe that, as it turned, contacted an “elastic spring arm” that was insulated and threaded into the side of the cylinder head. Battery voltage passed from the spring arm to the lobe when they made contact, a spark being produced upon the breaking of the two. The spring arm could be adjusted to compensate for wear and was designed to be easily replaced as necessary.

Black white photo of an engine with the specs of each part

The engine was throttle-governed, the governor working a throttle valve via a connecting arm attached to the governor, pulling the throttle valve shut as engine speed increased and allowing the throttle to open as the speed decreased. Throttle valve tension could be adjusted to fine-tune engine operation. The engine also featured splash lubrication. Small chambers cast into the bottom of the piston collected oil splashed by the crankshaft when it dipped into the crankcase, metering it out as the piston rose and fell, any excess passing out through channels in the piston.

Although an intriguing design, we can’t help but think it would have been unreliable. One has to wonder about the reliability of the “elastic spring arm” for the igniter, and then there’s the question of wear on both the cam lobes and the discs they contacted. The lobes appear almost square cut, with no ramping whatsoever to cushion their contact with the discs. Proper heat treating would help, of course, and in practice, one would imagine the lobes would be bathed in oil. It’s unclear whether any manufacturer took up Raymond’s design, but we do know that he went on to work for Standard Automatic Gas Engine Co., Oil City, Pennsylvania, where his name was assigned to various patents.

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