hydraulic cylinder rebuild procedure

wowbw7 · Mar 12, 2008

New member here, but Ive been reading the posts and am quite impressed with the knowledge of some of your members. I have a question about rebuilding cylinders. Last summer I purchased a late 60's tractor/loader/backhoe in need of some cylinder rebuilds. I rebuilt the boom cylinder after purchasing the kit from Martin Fluid Power (www.mfpseals.com). I got the parts numbers from John Deere online & went to Martin and saved a bundle. 50% off online orders! Anyway, 1 pack of seals, I believe for the piston itself, is a stack of 6 V-shaped seals. The repair manual addresses this pack by saying how, at the factory, the seals are installed with the V pointed away from the bottom of the cylinder using special tools. But that installing them in-the-field, the V should be installed pointed toward the bottom to ease installation (so the outer lips of the V don't catch on the cylinder when pushing the piston into the cylinder). This makes sense to me, as the factory installation forces the seals outward against the cylinder wall. But I would like to know (as I plan to rebuild 5 more of the cylinders on this unit):
1) Has anyone had experience with this type of seal pack?
2) And wouldn't a piston ring compressor tool (like used to install Piston & Rings into engine blocks) work to compress the seal pack so one could install them the 'factory' way?
thanx in advance for any replies

Wayne County Hose · Mar 12, 2008

wowbw7 said:
New member here, but Ive been reading the posts and am quite impressed with the knowledge of some of your members. I have a question about rebuilding cylinders. Last summer I purchased a late 60's tractor/loader/backhoe in need of some cylinder rebuilds. I rebuilt the boom cylinder after purchasing the kit from Martin Fluid Power (www.mfpseals.com). I got the parts numbers from John Deere online & went to Martin and saved a bundle. 50% off online orders! Anyway, 1 pack of seals, I believe for the piston itself, is a stack of 6 V-shaped seals. The repair manual addresses this pack by saying how, at the factory, the seals are installed with the V pointed away from the bottom of the cylinder using special tools. But that installing them in-the-field, the V should be installed pointed toward the bottom to ease installation (so the outer lips of the V don't catch on the cylinder when pushing the piston into the cylinder). This makes sense to me, as the factory installation forces the seals outward against the cylinder wall. But I would like to know (as I plan to rebuild 5 more of the cylinders on this unit):
1) Has anyone had experience with this type of seal pack?
2) And wouldn't a piston ring compressor tool (like used to install Piston & Rings into engine blocks) work to compress the seal pack so one could install them the 'factory' way?
thanx in advance for any replies

Welcome to TBN. I'll answer this as best I can, but I am assuming that these are all double acting cylinders.

First, I have rebuilt loads of cylinders with this fabric style packing. I would install the new seals as the old ones came out. The "cup" part of the Vee packing should face the pressure, otherwise the fluid will leak past and the cylinder will not hold pressure. So, looking at this series of vees as your piston seal, the open part of the vees should face fluid pressure. <<<<<pressure. This setup can easily be installed in the "field." What you want to do is get everything assembled on the rod. Place the cylinder housing in a good holding fixture. Oil the piston seals very liberally, let it drip. NO GREASE! Now take the rod assembly and insert it into the cylinder housing as far as it will easily go. Now, wiggle the rod in a circular motion while pushing it into the cylinder. It will go, trust me.

A piston ring compressor will not work. What they are doing is putting a specially made sleeve over the seal and between the housing threads. The ID of this sleeve is the same ID as the cylinder housing. You can do the same thing with some house flashing. Not necessary for this style of seal, but if it eases your mind, try it.

I like these guys for seals, Hercules Sealing Products. You can buy the kits, or seals individually. With your type of seal, sometimes I like to mix in a urethane seal among the kit. This helps with low pressure sealing. Basically, helps prevent drift. The fabric style does not seal well at low pressures. Believe it or not, some seal styles do not seal well until they get a good amount of pressure behind them. The higher the pressure, the harder the seal is pushed into the cylinder housing, the result is a better seal. Also, the more Vees in the set, the more pressure the cylinder will hold, so make sure to put the same amount in as came out.

This is why I do not like John Deere products. You do it their way, it will not work. They try to scare you into either having them do the work or buying their products.

wowbw7 · Mar 12, 2008

Hey, thanx, HOSE, for the help. I'm gonna try your way on the next one I tear down. One more question thats always been in the back of my mind when it comes to these cylinders...is there a reason why the opened end of the cylinder couldn't have a short tapered section to make installing the piston alittle easier so tearing the seals would be less likely? or is there a strength or pressure issue here?

Wayne County Hose · Mar 12, 2008

A tapered section? That's more machining costs. It sounds sensible, but not practical. Wall thicknesses, machining, threads and glands to deal with, nope.

And, an afterthought. I do use a piston ring compressor on certain types of seals. Some piston seals, you have to heat in hot water to make them more flexible, then, stretch it over the big ends of the piston to install it on the piston. The compressor helps to shrink the seal back to it's original size.

wowbw7 · Mar 12, 2008

what do you think of plugging the cylinder with an oily rag and grinding the sharp ridge off the cylinder with a dremel to lessen the chance of a ruined seal when twisting the piston in?

Wayne County Hose · Mar 13, 2008

You definately don't want any sharp edges. Just be very careful where and how you grind. I would try a file first. Also, any material you remove is a system contaminant. When working with hydraulics, be clean.