The Power-Wagon Governor
Click for larger image
    A variable speed mechanical engine governor was an available option on the 1-ton Power-Wagon models WDX through W300M produced from 1946 through 1958. This governor was intended for use in conjunction with the rear PTO tail shaft and belt drive pulley options, also offered on these trucks. It was designed to regulate a steady engine speed when applying a varying load to equipment operated from of the tail shaft or belt pulley.

Click for larger image
    The original governor was manufactured by the King-Seeley Corporation of Ann Arbor, Michigan, for most of the years it was available, and also for a period of time by the Pierce Governor Corporation of Anderson, Indiana. There appears to be no outward differences between these two governors manufactured by these two companies. It has not been determined exactly where the design originated. The original Power-Wagon governor bears little resemblance to others manufactured by these companies. It has features unique unto itself that sets it apart from the others. Early Chrysler photos (some appearing in parts books, shop manuals, and service bulletins) show features that differ from those known to exist on original governors found on Power-Wagons now in collectors hands. These differences are minor and seem to be fairly prototypical.

    The mechanical engine governor was used only in conjunction with the early "square top" CARTER CARbureTER. This carburetor consisted of the following models: ET1, ET2, ET4, E7F1, and E7S1, all of which used the integral velocity type maximum engine speed governor. In these models, the governor, not the carburetor, housed the throttle plate. These five models are of similar design and fully interchangeable. These carburetors were standard equipment on Power-Wagons manufactured from 1946 through 1952.

    In 1953 the "square top" carburetor was replaced with CARTER models E7T1 and E7T2 which housed their own throttle plate. These carburetors, in turn, sat upon a separate sandwich type governor that was used to regulate maximum engine speed. The exceptions to this rule are found on a few Power-Wagons manufactured from 1953 through 1958. These trucks, when special ordered with the mechanical engine governor option, were again fitted with the old E7S1 "square top" carburetor with integral velocity governor. The mechanical governor assembly ceases to exist in parts manuals after 1958. It is apparent that the mechanical engine governor was designed to work only with the velocity type carburetor governor and only on the 230 c.i. L-head engine.

How a Governor Works
Click for larger image
    A mechanical engine governor works on the principle of centrifugal force. In the case of the original King-Seeley and Pierce mechanical engine governors, a V-belt, which is driven by an additional pulley mounted between the engine's water pump and radiator fan, provides rotational force to a mainshaft within the governor. Attached to this rotating mainshaft are levers hinged in such a way that one end of each remains connected to the shaft at all times and the other end is allowed to freely swing away from the rotating axis of the shaft.

    On the free end of each of these levers is a flyweight. These flyweights assure that, as the rotational speed of the shaft increases, the levers swing outward in reaction to the increase in speed. Centrifugal force from the combined rotation of the shaft and inertia of the flyweights creates force upon the levers and allows them to control movement of other components within the governor through leverage. This leverage is transmitted out of the governor through a rockshaft to which is attached a lever arm. This arm controls movement of a telescopic linkage assembly ultimately connected to a carburetor throttle lever, which controls the position of the throttle plate located in the carburetor's integral velocity governor.

    As the rotational speed of the engine increases, the resulting centrifugal force created within the governor causes the throttle plate in the integral velocity governor of the carburetor to close via the resulting movement of the interconnected governor lever arm and linkages. In short, as the engine speed increases, the governor closes the throttle slowing the engine. This centrifugal force increases proportionally as the engine speed increases.

    With a governor operating simply as described above, the engine would be allowed, or "governed" to run only at idle. Any increase in engine speed would be met by an immediate reaction from the governor causing the throttle to close.

    An additional feature of the governor allows for the regulation of engine speed above idle. This is achieved by the use of a spring. This main governor spring is attached by one end to the external levers and linkages of the governor. Its other end is attached to a mounting point. The spring is oriented in such a way as to provide opposing force to the centrifugal force created within the governor.

Click for larger image
    Whereas the force from the spinning flyweights causes the engine to decelerate, the force from the mainspring causes the engine to accelerate. The force from the spinning flyweights and mainspring equalize and cancel out one another resulting in an engine RPM of a given speed. This given speed varies depending upon the tension built into the spring. Greater tension results in the governor equilibrium occurring at a higher RPM and lower tension results in the equilibrium occurring at a lower RPM.

    On some governed equipment, such as an engine providing power for a welder for instance, only one set speed of rotation is desired, so the mounting point that the spring connects to is fixed at a permanent location. This desired speed is determined by the amount of power needed to propel the equipment for its intended purpose. In the case of a Power-Wagon driving a tail shaft with the potential of operating various forms of farm and industrial equipment, the need exists for variable governed engine speed in order to match the requirements of the particular equipment at hand.

    This adjustable feature is provided for in the original King-Seeley and Pierce and mechanical engine governors through a manual adjustment of the tension on the mainspring. This is accomplished by increasing and/or decreasing the static length of the spring via the location of an adjustable mounting point.

    The location of the mounting point is altered through a combination of linkages connecting it to a dash control speed selector Lever mounted to the underside of the dash within the truck cab. Moving the control lever, in such a way to cause tension on the mainspring to increase, results in a higher governed engine speed. Moving the control lever, to cause tension on the mainspring to decrease, results in a lower governed engine speed.

    One final feature of the King-Seeley and Pierce governors, as found on the Power-Wagon, sets them apart from most of the others. This unique feature is found in the driven v-belt pulley mounted to the mainshaft of the governor. This pulley can be easily disengaged from the governor mainshaft by an integral dog clutch. This allows it to free wheel as required in order to use the truck for transportation on a highway. With the pulley freewheeling, the idle governor no longer has any influence over engine operation or speed.
Vintage Governor Service Bulletin

-Clint Dixon

Last Updated:

Copyright © 2004- - Clint Dixon
All Rights Reserved