Engine governors were the mechanical solution to speed control
This photo of the governor on a John Deere tractor shows the linkage from the governor to the carburetor.
Imagine driving a tractor without an engine governor. You’d soon discover why governors are sometimes referred to as speed regulators. Without a governor, the engine would lug down every time you went up a hill and would rev up the minute you went down the other side. As a result, you’d constantly be adjusting the throttle.
The same thing would happen when the tractor encountered a load while pulling an implement. You’d have to give it more throttle to compensate, only to slow down in lighter soil. Fortunately, inventive minds found a solution to the problem long before internal combustion engines were even invented.
By most accounts, an engine governor is described as a mechanism that uses a rotating mass applied against a spring to adjust the carburetor throttle shaft to regulate the engine speed around a set point established by the throttle lever position. In other words, you set the throttle for the speed you want to travel and the governor’s job is to maintain that speed.
In nearly all cases, the governor is driven by the timing gear or by a drive coming off the magneto or distributor drive shaft and interconnected with the hand throttle linkage and the carburetor throttle plate. The rotating mass, meanwhile, is usually a set of flyweights or cams with weights at the end. However, in some cases, such as the governor used on Ford 9N, 2N and 8N tractors, a set of steel balls within a pair of races is used.
Engine governors are hardly unique to modern internal combustion engines, though. According to historians, centrifugal governors were used to regulate the distance and pressure between millstones in windmills as early as the 17th century.
Even as governors were developed for early steam engines, they were less than precise. However, that wasn’t as important then, since many early engines were used to pump water — an application that could tolerate variations in the working speed. A constant operating speed did not become necessary until Scottish engineer James Watt introduced the rotative steam engine used to drive factory machinery.
In 1788, Watt developed a conical pendulum governor that used a set of revolving steel balls attached to a vertical spindle by link arms. The controlling force naturally varied with the weight of the balls.
The earliest internal combustion engines required the operator to adjust the throttle in response to the load. It wasn’t until the development of multi-cylinder tractor engines in the early 1900s that throttle governors began to appear on tractors. By the 1930s, most tractors used variable-speed type governors that regulated speed around a set point determined by the throttle lever position.
As anyone who has driven a tractor built in the last 75 to 80 years knows, any change in engine load generally leads to a change in engine speed. The role of the governor is to regulate the supply of energy to the engine to bring the speed back to its original value. As the rotating weights move farther away from the rotating shaft, connecting arms cause a change in the position of a sleeve, which in turn moves a lever or shaft that actuates the fuel supply valve — whether it’s controlling fuel, compressed air, steam or water.
In most cases, governors are classified as either centrifugal or inertia types. Vintage farm tractors generally feature centrifugal governors. As the name implies, the governing effect is obtained from the change in centrifugal force on two rotating masses when an increase or decrease in governor speed occurs.
The first step in governor inspection, should you suspect a problem with a tractor or as part of a restoration project, is to check for signs of malfunction. The engine may idle too fast or may fail to idle down when the throttle lever is moved to the idle position; the engine may surge or over-rev; the engine may fail to reach the specified top speed; engine speed control may be erratic; or there may be delayed or sluggish response to changing load conditions or throttle movement.
One way to test a tractor’s governor is to drive up a slope in one of the higher gears with the throttle partially open. When the engine load gets to the point that forward speed begins to drop, the governor should kick in, automatically opening the butterfly to give the engine more fuel to maintain set engine speed. If the engine doesn’t try to maintain speed, it’s a good indication the governor is not working properly.
Before removing the governor or attempting any disassembly, check the condition of any external springs, such as the one used on the Ford N-Series governor. On most models, though, the governor spring will be enclosed in the governor housing. Also inspect all linkages and link rods for free movement and the absence of bends or binding.
A maximum speed set screw on most governors can be adjusted to increase or decrease the maximum rpm setting. If the governor reaches the maximum speed stop setting before the hand throttle is in the wide open position, or if the governor fails to reach the maximum speed stop before the hand throttle is wide open, it may be necessary to adjust the connecting rod linkage between the governor and the carburetor. Refer to a service manual written for your tractor model to determine the correct procedure for maximum speed adjustment and linkage adjustment.
Your manual should also have a procedure for governor overhaul; the basics include inspecting and replacing defective bearings, seals and drive gears. Also, ensure that the flyweights move freely, or in the case of flyball governors, make sure the balls are free of flat spots, pits and excessive wear. The inner surface of the cone race should be smooth and even.
If you’re not sure of your ability to rebuild the governor, you might consider sending it to a shop that specializes in governor restoration. Keep in mind, though, that if you replace any parts, they must be identical to the original. Replacing the throttle-to-governor spring with a lighter spring, or one with less tension, for example, will cause the governor to “hunt” for the right speed.
Remember, some mathematical wizard long ago calculated the appropriate tension on the spring, the weight of the flyballs and the length of the connecting arms so the governor could do its job of governing. It appears that he or she got it right. FC
For more information: Portions of this article originally appeared in How to Restore Classic Farm Tractors: The Ultimate Do-It-Yourself Guide to Rebuilding and Restoring Tractors by Tharran Gaines. Reprinted with permission from the author and Voyageur Press.
Tharran Gaines is the author of five books on antique tractor restoration and writes a variety of materials for AGCO Corp. He is also a contributing editor to AGCO Advantage and Massey Ferguson Farm Life magazines for AGCO. Email him at email@example.com; online at Gaines Communications.