Posted by LenNH on November 11, 2009 at 10:28:53 from (71.192.137.159):
It's fun to write about stuff you love. I thought it might be useful to some of the younger folks who are just beginning to work with the "old" stuff to write about the difference between a variable governor (probably universally used since about 1937) and a throttling governor. The term "variable governor" is obvious, I guess, but what it means is that not only can the speed of the engine be varied, but that the governor actually works over a range of speeds. You can set the governor lever at, say 1000 rpm, and the governor will maintain that engine speed if the tractor is capable of pulling the load. Some of the IHC literature I have for the H and M actually gives the range of governed speeds. In this type of governor (at least, the ones I've seen), there are no springs on the weights. The operator moves a lever or a rod, which pulls on a spring that is attached to rods and levers that go to the carb butterfly. The weights work AGAINST this spring. In other words, the operator trys to open the throttle valve, while the governor weights resist this opening. This is a balancing act: A certain amount of spring tension will pull the throttle open and the governor weights will provide just enough counter-tension to keep the speed at the desired level. This counter-tension depends on the centrifugal force at varying speeds. "Throttling governors" (as I understand the t erm--I think I am using it correctly) were used on most International Tractors in the 20s and on up into about 1937(10-20, Farmall, F-20, and so on, but NOT F-12, which had a variable governor from the beginning). There were probably a number of other tractors in those days with similar governors, but I don't know enough about them in detail to say. In this type of governor, springs BETWEEN the weights try to open the throttle, while the weights fly outward under centrifugal force and try to close the throttle. This again is a balancing act, but there is only one setting at which the governor actually works--when the throttle lever is set to "wide open." Spring strength could vary this speed (compare the 10-20 at 1000 rpm, and the very-similar F-30 engine at 1250 rpm--I expect they have somewhat different spring tensions, but I don't have complete parts lists to check that, and would probably be too lazy to check even if I did have the lists!). With the throttling governor, there may be some slight governing action at just below the wide-open setting, but I can't testify to that now (used three or four tractors with the throttling governor, but that was almost 60 years ago and my rapidly-aging mind no longer remembers exactly what happened when you throttled back just a little). I do know that if you throttled back much, you slowed the engine down, but the governor didn't do anything. This was a real pain on light belt work with the engine throttled back. If you set the governor for a certain speed with no load, then the load would pull the engine down. If you set the governor for a certain load, then removing the load would let the engine speed up a lot. The same thing happened in the field. I used to rake hay with an F-20 with 36" wheels (capable of about 6 mph in 4th, I believe), pulling an old slow-speed horse-drawn side-delivery rake which would overspeed and clank like an angry ghost in chains at much over 3 mph. To keep the noise down, I'd try to use 3rd or 4th gear, throttled way back. You could set the throttle for maybe 3 mph on the level, but the first upgrade meant that the engine died down, and the first downgrade meant that the engine speeded up. I have strong memories of keeping two fingers on the throttle lever in front of the steering wheel. Eventually, IHC got the message and converted to variable governors around 1937. An F-20 or similar tractor would have been a much sweeter package with the new governor. I suppose that one reason for the old-style governor might have been that that was the way it was done in the early days, and also perhaps because tractors weren't expected to do delicate things. They plowed wide open, and they operated belt-driven machines like threshers wide open, period. Funny thing is that the early Farmall was an "all-purpose tractor," designed to do light work as well as heavy work, and farmers who used them had to deal with the governor issue when they raked hay, cultivated small corn, etc. Unless, of course, they just plunked it into low or second and opened the throttle--the easy-but-noisy way.
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