Patent Page: The First Overhead Cam Engine

We take a look at what could have been the first overhead cam engine, patented by an engineer in 1892.

| June/July 2019

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.



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