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Discussion Starter #1
I've rebuilt 7 cylinders since acquiring my tractor and some implements over the past few years. Between YouTube and a local hydraulic shop, I've had pretty good luck. Until now.

I have a #74 front plow. There are various configurations of this device such as 74, 84, 366 and others, depending on the attaching parts, that fit different models of tractors. One part they all seem to have in common is a pair of single acting cylinders for angling. These cylinders have a small hole near the end to allow air to exit/enter as the piston travels. Moisture gets into this part of the cylinder. When I rebuilt them a few years ago, I notices a small amount of pitting near the end of the tube. I cleaned it up the best I could with very fine scotch bright pad.

The plow has been unused for two years as we've not had enough snow to justify the use. I've just installed it and these cylinders are leaking again out of the holes. I suspect I should have done a better job of removing the pitting. I've ordered two rebuild kits and will be rebuilding them over the holidays. Its not severe enough to prevent them from functioning but they do drip when sitting.

I've done some more research and there's plenty of guidance about honing cylinders when rebuilding but it isn't clear how tight the tolerances need to be. I'm planning on honing them to see if I can remove the pitting.

Question - how much I can hone them? I see one video where the gentleman hones them and puts them back together without seeming to do any measuring. Another article suggest the need for tight tolerances. I suspect application matters - there might more risk with a crane application than a snow plow application.

Thanks.

BTW, JD wants about $725 per cylinder and the tubes alone are over $400 - ouch. Long term, I'll probably end up replacing them. I checked online and could not find comparable cylinders. There are some snow plow cylinders that are similar but not quite the same. I'm pretty sure my hydraulic shop can fabricate the tubes cheaper (maybe).
 

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Discussion Starter #2

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Yes, as I wrote in that thread:

I went through the very same issues years ago with my #380 blade, and everything JAllen has written is 100% correct. There are no direct replacement aftermarket cylinders available, some are close and could be made to fit with some modifications to the cylinders and/or the blade frame but still not that easy. I honed mine, replaced the seals and they have been OK since, I also remove the blade from the frame, and store it in the off season with both pistons extended so there is oil in both bores.

It is indeed a very poor design :banghead:

I did not do any measuring, just made sure all the ridges and rust was removed.

Luckily (where is the knock on wood emoji?) the cylinders on my new blade for the 3720 are perfect so far.
 

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J, There's no "magic" involved with honing. The purpose of honing is to better the surface finish so the seals don't leak/bypass fluid. If you hone and make 90% of the inner surface perfect, that last 10% of poor finish is either going to leak or tear the new seals you just put in! Hone until you don't see any pitting/scratches/rust/poor finish and then re-assemble the cylinder. If it leaks, the cylinder tube is just plain worn out beyond use! Bob
 

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J, There's no "magic" involved with honing. The purpose of honing is to better the surface finish so the seals don't leak/bypass fluid. If you hone and make 90% of the inner surface perfect, that last 10% of poor finish is either going to leak or tear the new seals you just put in! Hone until you don't see any pitting/scratches/rust/poor finish and then re-assemble the cylinder. If it leaks, the cylinder tube is just plain worn out beyond use! Bob
At that point I’d take it to a hydraulic shop to see if it would be possible for them to find some slightly oversized seals to replace the originals with to see if there could still be some life-use left in the cylinder. It wouldn’t be perfect, but then again, no repair ever really is-and if it provides some additional useful life to your implement at a nominal cost then it would probably be worth it-certainly would be less costly than replacement.
 

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Where I worked years ago, we did quite a bit of hydraulic work. If we had issues with some cylinders or rods, sometimes we would have the barrel or rod either metalized or a new one fabricated. Especially if the cylinder was not available anymore or very expensive.
 

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Discussion Starter #7
Update

Here's an update that may help somebody in the future.

I bought a cheap cylinder hone online - one of the spring loaded ones that takes 4" stones. It came with fine grit stones.

I took the first cylinder apart and it was pitted far worse than I expected. I was not deterred - I bought a hone and i intended to use it. After about 30 minutes, the stones were wore out, the bore was polished and the pits were still there. I purchased a set of course stones and a set of fine stones on line. Back to the shop a few days later. I went through the course stones pretty quickly and turned to the fine ones. There's less pitting but still pretty bad.

Since I was off work and wasn't sure I was on the right path, I took it to the big city and visited the local hydraulic repair shop. They were pretty helpful. They didn't think I'd be able to get all the pits out and have it hold - basically thought I'd be removing too much material. And, they estimated it would cost me more for them to fabricate a new barrel than the cost of a new one from JD. Shop time is pretty expensive for custom work. They were willing to take it on but they didn't think it was worth it. He was not surprised JD wanted a lot more for new ones than snow plow companies like Western and Meyer. Apparently JD's reputation for expensive parts is more wide spread than I was aware. (OK - that's a bit snarky but $660 is a lot of money for a single acting hydraulic cylinder.)

The other interesting thing they pointed out is the poor fit between the barrel and the "end cap" - he actually believes that is leaking water into the barrel around the 'end cap' because there's no seal between the cap and the barrel. He was pretty funny - told me I should charge my neighbors for helping them with the next big snow to pay for new cylinders.

I ordered some more coarse stones, a set of medium ones and another set of fine grit. Back to the garage today. I went through a set of coarse stones and the pits are no long visible I honed with the medium and fine grit ones to clean it up the scratches. New seals seem to fit tightly. I re-installed it and it seems to be working fine - for now.

I suspect it will start leaking again sometime but I imagine it will work for a while. Given I've only used it twice in 3 years, I think I'm good for now. Maybe tomorrow I'll start on the other one.

Here's a little reminder from high school geometry class - the pattern of pitting was a parabola. A plane intersecting a cylinder at a non-zero angle creates a parabola. When the water was in the cylinder, they were tilted back a little so it rusted in a parabolic shape.
 

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Thanks for the continuing updates JA!
 

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Sometimes persistence pays off. Hopefully you get many more years of good service from it.
 
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