Posted by LenNH on February 18, 2010 at 08:28:11 from (24.60.236.239):
A recent post was from a fellow who wanted to understand better how a governor works. One of the replies compared the governor weights to something heavy attached to a string. This was a good comparison--as the string is spun faster, the weight goes out. In a governor, the weight going out would tend to close the throttle, through a linkage system that doesn't need to be described here (the linkage would vary with the engine, location of the governor itself, etc.). If you have a fairly "modern" tractor (with IHC, this means letter series, or 1939 and later), you have a "variable governor." In this system, there is a range of speeds over which the governor works to maintain engine speed. The governor control ("throttle lever" is what most of us would call it) pulls a spring which is attached through linkages to the carburetor butterfly valve. The farther the lever is pulled toward "fast," the more the butterfly valve is opened. The governor weights work against this spring, in effect. If the operator has set half-throttle, the governor weights will move in and out as necessary, moving the butterfly valve slightly, to maintain the desired speed. There are no springs on the weights of variable-speed governors.
Many earlier tractors, including most of the IHC numbered series except F-12, had what I used to hear called a "throttling governor." The weights on this type of governor have springs that tend to pull the weights together toward "wide-open throttle" position. The spring forces were calibrated to give a certain full-load speed (like 1000 rpm on a 10-20). If the throttle lever were removed, nothing would happen except that the engine would run at the full governed speed all the time (in this case, somewhat higher than 1000 rpm if there was no load). If you look at the mechanism of the earlier IHC governors, you will see that the throttle linkage goes over to the left side of the engine. Inside the little round box, there is a lug on the butterfly-valve shaft. When the throttle lever is pulled toward "slow," the little lever you can see on the outside just engages this lug and closes the throttle. The result is that the engine slows down, but that there is no governing action. I used to rake hay with a '36 F-20, and to avoid a lot of noise, I tried to run in 4th gear, throttled way back. Great on level fields, but a real pain going up and down hills, because you had to constantly adjust the throttle lever to keep the ground speed steady. With a variable governor, you have full governor action at a certain point somewhat above idle speed. On this old-style governor, there is a SLIGHT adjustment provided for the full-load speed. This is that little bulb-like thing that sticks out the back of the governor housing. It can be turned to vary the tension on a spring that works on the throttle linkage after it leaves the governor weights. IHC added variable governors to the "old" tractors sometime in the middle thirties. I'd have to do some looking at parts books and such to get an exact date, but I am going to say that this happened in about 1937. The factory-installed variable governor has a bellows coming out the back of the governor, and a pull-rod which goes to the operator's station through whatever linkage makes it work for a particular model. On an F-20, the throttle control is a flat, notched "rod" very similar in appearance to the throttle on an F-12. This "rod" is on the LEFT side of the gas tank. IHC made a kit to install the new-style governor on older tractors. This is very similar, but the notched rod is on the RIGHT side of the tank. Several outside manufacturers made retro-fit variable governor kits. Some of these have a decidedly clunky look in the rods and levers that end up in front of the driver. One quick tipoff to the presence of a retrofit governor kit is the original throttle lever, which was seldom removed because its shaft supports the spark lever. I hope this makes sense. It does to me, but maybe that is only because I spent over 10 years driving tractors with the "throttling governor," and many more years driving tractors with the "variable governor." Somewhere, in my so-called collection of parts books, brochures and the like, I probably can provide pictures of all the things I tried to describe. I'll get on this "when I get a chance," as we used to say for things we just might get around to sometime.
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