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I have a grasshopper 725D mower. This is a 3 blade ztr mower.

Blades are mounted on 1"shaft that passes through a pair of 1" x 2" x 1/2" bearings. Bearings rest on a step in the spindle case, and also have a sleave that supports the centres. The spindle housing is about 2.5" in diameter.

The blade is bolted with a 3/8" NCF bolt to the shaft. There is a metal washer between bolt and blade about 2" in diameter, and a fiber washer between blade and bearing.

In operation if you hit any plastic bailing twine it wraps tightly between the blade and spindle housing, then melts and moves into the space between the fiber washer and the bearing. There it destroys the bearing seal. Net result is a $200 repair about once a season.

I'm looking for ways to prevent the plastic from melting and getting into the bearing space.

One thought I had was to fabricate a metal cup that went between the blade and the fiber washer that covered the spindle housing. This would spin with the blade. However the top edge of this would have to have some clearance, and I anticipate that it would collect dust, mud, shattered dry grass. Not sure if this would be a win or not. I also worry about water collected there, as I frequently have to mow wet grass.

This must be a frequent problem in mechanical engineering -- running bearings in a hostile environment.

Pointers to any standard ways to deal with this.

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I would install a drag rake under the front end of the mower to snag the string before it gets into the blades.

Failing that, I would replace the bearing with one that has a metal shield that won't melt like the urethane or neoprene shields will.

Also consider inspecting the mowed area for string before starting the job. it might take your assistant an hour to do so but if that costs you $25 then you still come out ahead.

while the spindle assembly is out of the mower deck I would also install a grease fitting into it so you can pump the insides of the spindle housing full of lube at the end of the season; this will prevent water from collecting inside it where it will ruin the spindle bearings.

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  • $\begingroup$ Steel shields are a good idea however. $\endgroup$ – Sherwood Botsford Sep 10 at 14:13
  • $\begingroup$ home-use mowers do not have spindles with grease fittings. Being a cheap engineer, I added them to mine so I wouldn't have them rust out on me. Up here, we use industrial mowers with great big trimmer string on tree farms; have you tried one of those? -NN $\endgroup$ – niels nielsen Sep 10 at 15:37
  • $\begingroup$ Mower is a grasshopper. 25 hp diesel. 20 yrs old is was $8000. Not a home mower. $\endgroup$ – Sherwood Botsford Sep 15 at 2:17
  • $\begingroup$ Spindle housings already have grease fittings. As the area is a tree farm and twine is used regularly for staking trees, and the grass isn't mowed until about 6" high searching for twine is counter productive. The mowing area is about 10 acres Walking the area on ten foot grid strips = 4200 feet per acre. This adds about 4 hours to the job, and finds about half the twine. Rakes clog almost instantly with clippings or thatch. $\endgroup$ – Sherwood Botsford Oct 3 at 2:56
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You're on the right track. Many commercial mowers have a disk (like a saucer) that mounts below the blade, has two cutouts for the blade, and curves up to catch string and stuff. We have about 10 acres of ponds and a lot of sneaky fishermen. We mow about 150 acres each week, and can pull a drum full of fishing line out of our mowers over the course of a season. But we check and clean all the decks several times a week. I haven't changed a bearing in our '80s Toro 228D in ten years.

Couldn't get the image to load, so here's a link to a groundsmaster deck showing the disks - https://cdn2.toro.com/en/-/media/Toro-Media-Sharepoint-Libraries/_Images/ProductCatalog594X694/7GaugeWeldedSteelDecksGM7200_SteelDecks,-d-,jpg.ashx?mw=600&mh=171&hash=C0058CCAB12B449FE2D4495937D6F99BA6C8EFA7

[edit] Jinxed it—I threw a shaft bearing on the 228 yesterday.

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