Reversible 4-Cycle Engine Patent

By Staff
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Selectively engaged cam/rocker/pushrod sets acting upon a sliding ignition/valve block (no. 3) allowed engine reversing, at least in theory.
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Closeup of the individual cam lobes for forward/reverse.

We’ll never know precisely what inspired Frederick T. Flinchbaugh to patent a reversible 4-cycle engine, Patent no. 874,177, granted Dec. 17, 1907, but clearly Flinchbaugh, whose Flinchbaugh Manufacturing Co. built York engines in York, Pa., perceived an opportunity for increased engine sales if he could design a reversible 4-cycle engine for farm or small shop use.

Although 2-stroke engines can run in reverse — after being fully stopped — Flinchbaugh’s goal was a 4-cycle engine that could reverse direction on the fly. According to his patent, that goal could be met by selectively employing one of a pair of cam faces to act upon one of a pair of rocker arms, actuating one of a pair of pushrods connected by way of a coupling to a sliding block on the side of the engine. As the sliding block (no. 3 in the main drawing) was pushed forward by a pushrod, it actuated both the igniter and, after a suitable lag, the exhaust valve.

According to Flinchbaugh’s patent, with the engine running in a given direction, the operator moved the control handle to initiate a change in engine direction. The handle operated linkage shifting a coupling connecting the pushrods so one or the other pushrod acted on the ignition/exhaust sliding block. The cams were profiled such that when the operator initiated reversal by shifting the coupler, changing which cam/pushrod set was driving the ignition/exhaust slider, ignition timing would instantaneously switch to cause ignition “out of regular order so as to drive the piston in the opposite direction and thereby give an initial impetus to the engine for reversing.” The set not employed simply idled during operation.

In theory, at least, it should work, but one would imagine the engine would have to be moving very slowly to reverse direction without cataclysmic results. Flinchbaugh gave this fact tacit recognition stating, “It is not expedient to operate the reverse mechanism when the engine is running at high speed and it is preferable to materially reduce the speed to bring the reverse mechanism into play.”

Given the fact such an engine never appeared on the market — from Flinchbaugh or anyone else, as near as we know — it’s probably safe to assume that Flinchbaugh’s design, if it even made it to the full prototype stage, was an impractical solution to an issue that already had a solution – the reversing clutch.

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