Compound V4 Heisler

Updated: 7/1/2023

In May of 2021, I struck upon an idea. Heisler locomotives make use of a V-twin engine to turn a drive shaft. Extrapolating from that, why not increase the number of cylinders to create a V4 engine. Such an arrangement would allow compound expansion to increase efficiency. I realized that this engine should have a crank angle of 180° to idealize the balance, which allows rocking bars to be used to derive two of the four valve positions from the opposite valves on each piston bank. This makes a second set of valve gear redundant. This principle is shared by Great Western Railway (GWR) and LMS flat 4 engines:

In the early days of steam engine design, many engineers cared little for the balance of their engines. The science of engine balance was underdeveloped at the time so little to no one knew how to properly balance engines to minimize wear. Many designers didn’t even bother to add basic crank shaft counterweights. Many, but not all, Shay inline 3 engines lack any balancing elements.

Shay Engine Without Counterweights

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Heisler V-twin engines did at least have crank shaft counterweights to improve but not perfect their balance. On the other hand, a V4 engine with a bank angle of 90° and a crank angle of 180° has near perfect balance. The only reciprocating weight that would not be balanced is that of the valve gear and arcing connecting rods. In comparison to pistons, the forces added by valve gear and arcing rods are negligible. Therefore, in several ways a V4 compound engine is the ideal type of engine for a Heisler locomotive. Shortly after coming up with this idea I discovered that Charles Heisler had already filed a patent for the idea 125 years earlier on June 22, 1897. Unfortunately, we don’t have any documentation to prove this locomotive design was ever built. A G-gauge model has been made which proves the principles of the engine work:

High Quality Schematic:

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Full Patent Page:


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