I have been reading this board for a while, but have only posted once. I was raised on a farm where the largest tractor we ever had was a WD Allis Chalmers (about 45 hp). My Dad made 26 crops with that tractor, we farmed about 80 acres of cotton and soybeans (back then, you could make a living on that). We had a pull type bush hog that we used to mow around our old barn and sheds, cut down the cotton stalks after harvest, and mow about 8 to 10 acres of "layout ground". Sometimes we ran the tractor at wide open throttle (cutting stalks especially, you wanted to get that job done in a hurry, usually it was done in late Nov. or Dec.), but when mowing around the sheds and barn, and in the layout ground where you often hit holes, we throttled back a bit, and ran in a lower gear. The only thing we ever did to the bush hog was replace a shear pin occasionally, and fix a flat once in a while. When we sold it, the gear box, seals, etc. were all in good shape. Running at less than 540 rpm never hurt them in the 20 or so years we had the thing. We did overhaul the tractor once, but I doubt the little time that it spent running the bush hog had as much to do with that as the many hours pulling the disk, tumbling harrow, cultivators etc. did. By the way, there was no tach on the tractor, so we didn't know what rpm the bush hog was turning anyway. If the ground speed was comfortable, the tractor wasn't lugging and the cut was okay, that was all that mattered.
I now own a NH TC 30 that I use to spread dirt, chat, gravel, etc. I do some work for a contractor around new houses he builds, and put an ad in the paper to get a little extra work. I teach World History at the local high school, and do these jobs right now to pay for the tractor. Hopefully, later on when I retire, the tractor will be paid for and I'll use it to supplement my retirement. I have only done one mowing job with it, which amounted to cutting the waist high grass around a new house where I was doing the dirt work. I didn't run the bush hog at 540 as I didn't know what the carpenters had thrown out there, and I didn't want to throw anything through a window, so I kept the rpms at a speed where I didn't bog the tractor down and still got a good cut. I believe 540 is the speed for optimum cutting in tall thick grass, but you can run at a slower speed in sparse, not so tall grass, get a good cut, and not damage your tractor or bush hog.
