I acquired a used tractor built by a major Japanese manufacturer. It was a small diesel tractor with a three-point hitch and a mowing deck behind it. It worked fairly well, at first.
One day while I was cutting the grass, the mowing deck belt broke. This belt was very long. It extended past the three blade pulleys, two idler pulleys, and then to the big drive wheel attached to the shaft that goes to the power take-off from the rear of the tractor. I wrestled the mowing deck off of the tractor -- no small chore -- extracted the belt, and then marched off to the local dealer.
A new belt was $60. I brought it home and then wrestled with that belt to fit it on to the mowing deck. When I finally got it back together, I greased all the Zerk fittings for good measure, blew the grass clippings off of the deck, and then hopped back on the tractor.
I got the rest of my lawn mowed. A week or so later, I was out mowing again. The tractor isn't fast, but it has plenty of torque. While mowing through some deeper parts of the grass, the tractor makes a little bit more noise and throws off a bit more smoke. The clippings were flying. A couple hours later, toward the end of the effort, the belt broke again. I cursed and took the belt back to the dealer.
I showed him the broken belt and asked him what he thought might have caused it. He looked at it and asked, "You live close by?" "Yeah," I replied. "Go home, and bring back the idler pulleys." Puzzled, I drove home and unbolted the two idler pulleys. They both seemed to spin smoothly. I shrugged, and took them to the store.
The parts guy spun the first one and said, "This one is OK." He spun the second one and then said, "You've got galled bearings on that one."
I said that it was spinning just fine. He pointed to it and said, "Listen to the bearings as they move. Notice the play in it. When this thing gets hot, it will seize." He said he could replace the bad bearing for $25. I also had to buy another new belt.
I wrestled the thing back together, with a bit more finesse this time. I reattached the mowing deck to the tractor. The mowing deck ran fine for several more seasons before I had to replace the other bearing. I now check the bearings once a year.
This entry was submitted by Jacob Brodsky and edited by Rob Spiegel.
Jacob Brodsky is a registered professional engineer in the state of Maryland.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
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