Replacing an end seal

[BrentD]

I was out changing some fluids on our Mitsubishi BD2G dozer over the weekend and noticed that one of the cylinders for raising/lowering the blade is leaking fluid from the end of the cylinder around the rod. I'm assuming that this means a seal is shot and needs to be replaced.

How difficult of a job am I looking at? The cylinder end cap appears to be in good condition and the threads look reasonably clean, not painted over or anything so I'm hoping it should be relatively easy to get the cap off. It also looks like I should be able to do this without completely removing the cylinder from the dozer. Looks like I can just undo the pin that attaches the rod to the boom, undo the end cap and remove the rod from the cylinder and replace whatever seals need to be replaced.

Is there a special wrench to remove the end caps? Looks like it's just got two square notches in the cap so it shouldn't be too hard to make a wrench. Any idea how much torque I should expect? Anything else I need to know before I jump into this head first?

 

[Wayne County Hose]

Post pictures of the gland (end cap) and we can tell you exactly how to disassemble and rebuild.
Andy

 

[BrentD]

Here's the entire cylinder:

Viewed from the top (sort of):

Dead-on:

 

[kennyd]

That should just screw off Brent, make a spanner if you can-worst case use a pipe wrench...And to make it easier-crack it loose while it's still on the machine so you don't have to worry about holding it. It will be pretty tight!

Is this a Grey machine? Either way the seals may be a oddball size or Metric...

 

[BrentD]

Is this a Grey machine? Either way the seals may be a oddball size or Metric...

Yep. Bought it from a guy who buys them direct right off the boat from Japan. I think this particular one came in via one of the Houston/Galveston ports.

It's a 1988 model and still runs like a top. Starts within 2 seconds of the the first turn of the key every time. Never a puff of black smoke out the tail pipe and I can buy the blade up against a tree trunk or the bank of the pond I'm renovating and the tracks will break traction before the engine even hesitates. Only down side to that is it's real easy to dig yourself into a hole in a hurry.

 

[BrentD]

Ok, I need some assistance... I got the end cap off, now I have a piece with threads around the rod and then recessed back a bit is what appears to be an O-Ring. I thought once I got the end cap off that the piston would just pull right out, but that doesn't appear to be the case. What do I do now? (My service manual is in Japanese so that's not really helping.)

Edit: Ok, it's not an O-ring, there is a round metal retaining ring that has to be popped out. No idea how to go about that.

 

[J_J]

That ring is what keeps the rod assembly from coming out of the cylinder. There should be a pin hole in the side of the cylinder to push the metal ring out. You may have to push the ring so the edge of the ring is close to the pin hole. If no pin hole, there is a space in the metal ring where you can put a metal pick and lift one edge out. Cover the end with a cloth so the ring does not spring out. Be careful with the pick, so you don't make any burs that might damage the o-rings.

Here is an illustration.

http://www.patentgenius.com/image/7455010-3.html

Expanded barrel hydraulic cylinder assembly - Drawing for Patent # 7455010 - PatentGenius

http://www.patentgenius.com/image/7455010-4.html

 

[BrentD]

Thanks JJ. Got the cylinder apart, now I've got to go get a 36mm socket for my impact wrench so I can take the rod apart and get to the seals.

 

[J_J]

Don't forget to put Lock Tight on the threads of the shaft, when you reassembly the unit.

 

[BrentD]

Don't forget to put Lock Tight on the threads of the shaft, when you reassembly the unit.

Which Locktite do you recommend? Blue or Red? (or some other?)

 

[J_J]

This one.

 

[tommu56]

BrentD
Another thing to check is the bushing behind the seal if its worn you will continue to have the seals fail.
I wouldn't worry this time but if it fails again put a new bushing in with the new seal.

tom

 

[BrentD]

tommu56> Thanks for the info. I've got to get the thing completely apart, but I "think" the repair kit I ordered might have the bushing with it. It has a white plastic seal that appears to go in the very end of the threaded inner part of the cylinder and a second rubber-bonded-to-metal ring that goes somewhere in there.... Won't know exactly where till I get it apart. Also found a damaged O-Ring that will need replacing too.

Next question: When I've got this thing back together, how do I go about purging air from the system? Should I try to pump some hydraulic oil into the cylinder ports before reconnecting the lines? (I'm really new to working on hydraulics if you can't tell.)

 

[kennyd]

Next question: When I've got this thing back together, how do I go about purging air from the system? Should I try to pump some hydraulic oil into the cylinder ports before reconnecting the lines? (I'm really new to working on hydraulics if you can't tell.)

The system is "self-bleeding", so all you will have to do is operate the loader through it's full cycle a couple of times to purge the air.

 

[BrentD]

Well, after ripping my old vice off my workbench, buying a new vice and a heavier impact wrench I finally got the nut off the end of the ram so I can get to the seals to replace them... Unfortunately I ened up having to heat the nut to get it off. I thought they used some seriously powerful loctite... Turns out it was a lock nut with a nylon insert. I melted out the nylon insert, and in the process I melted part of the bottom seal so now I have to order another part.

The big question is do I need to order a replacement lock nut, or can I just clean the rest of the melted nylon out of the existing one and put it back together with red loctite?

 

[kennyd]

I see no reason why Locktite would not work, just clean the threads with acetone or another strong solvent before applying.

Also-a tip for the future: Leave one end of the cylinder attached to the machine till you get the nut loosened

 

[BrentD]

Also-a tip for the future: Leave one end of the cylinder attached to the machine till you get the nut loosened

Yeah, that worked for the main outer ring/nut, the nut I'm talking about is the one inside the cylinder and the very base of the ram that holds the inner seal parts on. There was no way to remove that nut with the cylinder on the dozer, and I didn't think I was ever going to be able to get it loose with the tools I had. I'm not really sure my heating contributed all that much to breaking it loose. I think what finally worked was re-routing the air hose from my compressor in the garage so I only had to connect one 50' section to the impact wrench rather than two. (I'm also in the process of running PVC pipe to my workshop as a primary air line rather than depending entirely on the rubber air hose running around the garage, across the yard and in through the workshop door but that project is still just a stack of pipe and fittings at the moment.)

 

[kennyd]

You could have taken the rod(ram) back out to the machine and pinned it in place to hold it...but you got it done and that's what's important.

(I'm also in the process of running PVC pipe to my workshop as a primary air line rather than depending entirely on the rubber air hose running around the garage, across the yard and in through the workshop door but that project is still just a stack of pipe and fittings at the moment.)

PVC? You may want to re-think that...it can be VERY dangerous when used for air pressure. Do some searching on this one please. I used copper pipe cause it was easier than black iron pipe to get leak free.

 

[BrentD]

Ick. Never considered the rupture hazzard on PVC. Our local Crimestoppers chapter hosts a Haunted House as a fundraiser every Halloween and the building they have it set up in is completely plumbed with Schedule 80 PVC to run the animatronics so I just assumed PVC was safe since people that were supposedly professionals did the initial setup in that building.

On the cylinder seals the place I normally order dozer parts from doesn't carry those seals. Would a regular hydraulics shop be able to cross-reference the Mitsubishi part numbers?

 

[kennyd]

On the cylinder seals the place I normally order dozer parts from doesn't carry those seals. Would a regular hydraulics shop be able to cross-reference the Mitsubishi part numbers?

They probably won't cross the Mitsu numbers, but they can/will measure the old ones and be able to get you the correct ones. If you have that ability, then look at Hercules Sealing Products.

Ick. Never considered the rupture hazzard on PVC. Our local Crimestoppers chapter hosts a Haunted House as a fundraiser every Halloween and the building they have it set up in is completely plumbed with Schedule 80 PVC to run the animatronics so I just assumed PVC was safe since people that were supposedly professionals did the initial setup in that building.

Yes, it can be very dangerous. The Shed80 pipe they are using is certainly better than the Shed40 stuff from Home Cheapot or Lowe's.

In fact OSHA prohibits the use of PVC in above ground air/gas installations. Here is a couple links:

OSHA 1

OSHA 2

WoodCentral


I just want you to be informed...and safe.