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04/19/2011: "Stuff Breaks"

It's frustrating, but stuff breaks. It seems like the last couple of farm trips have been one step forward, two steps back... two weeks back I was mowing the south yard with the sickle bar mower; I could see the metal water pipe coming up clearly, and I had good clearance, until one of the mower wheels dropped down in a mini-gully. This sent the cutting bar just far enough over to catch the pipe, and it popped a rivet on one of the teeth. I straggled through the rest of the mowing, but I was disgusted with myself. My time was limited that day, and so rather than deal with it there and then I dragged the mower attachment home to work on one evening.

My other reason for bringing it home was that it has been a while since I've had to replace a tooth or a rivet on the mower attachment, and I was worried that I would get part-way into it and then have to go home, leaving a mess of parts sitting on the shop floor until my next visit. Since I do this kind of repair infrequently enough that it feels like the first time every time, I thought it would be a good idea to write it up for reference.

The first step is to remove the plastic guard with a 22 mm socket (two bolts, upper and lower). While not strictly necessary, this uncovers the work area in case you find out you need to get into it deeper.



Next, you remove two vertical bolts that go through a yoke assembly into the upper moving blade. These take a 13 mm wrench.



The blade is held down and constrained in its motion by six swing arms. You have to remove these swing arms; they're held in place by bolts that take a 5 mm allen head wrench.



Once you have taken off the swing arms you can carefully slide the upper cutting bar assembly out to the side.



Once the bar is out, you can deal with whatever happened to the cutter bar: typically when you hit something metal it will pop a rivet. Sometimes it will pop two rivets, and the tooth will come off completely. The first step in renovating the bar is to drive out any rivet remnants with a punch, which is shown in the photo at the head of this posting.

Once the old rivet is out you're free to replace it with a new one. Be careful, because there are two sizes of rivets: some rivets only go through the tooth and the bar, but others go through a tooth, a swing arm mount, and the bar. Once you have the right rivet, position so that it goes through the tooth with the head on the top of the bar. Then invert the bar, and put the rivet head, which is now underneath, on something hard like an anvil. Put on your safety glasses, get a hammer, and bash the end of the rivet until it fills the hole in the bar and is flush.



Re-assembly is the reverse of assembly, except that you should take a moment to apply some grease to the upper tooth bar where it slides on the lower bar, the sockets of the swing arms, and the yoke where it contacts the drive ferrule. Tighten everything tight, but not gorilla-tight; it probably won't be too long before you hit something else that pops another rivet...