Excavator Hydraulic Cylinder Repair

Dissmantling and repairing  a Hitachi EX150 Bucket cylinder.
Remove the flow tubes, grease fittings and pin wipers from the eyes
Strap the barrel down and put a bar through the barrel eye to prevent the barrel from turning. Match mark the gland to the barrel as the port in the gland must return to its position when reassembled in order for the flow tubes to line up again. 

 
Remove the eight socket head cap screws that hold the gland to the barrel. If you forgot to mark the gland have a look at the face of the barrel, there may be a blind hole that is not used, and this hole should have left a mark on the face of the gland.  Mark accordingly as after the parts are cleaned up for reassembly, you may not be able to see the mark any more.
 Have something ready to catch the oil when the gland comes out. Use a sling and a lifting device to support the weight of the rod, and slowly pull the rod assembly out.  Be careful when the piston gets to the end of the barrel. When the piston comes all the way out, if the rod is not properly supported, the rod will drop down and the nut the holds the piston on will mark the barrel right where the gland seals. Use the piston to meter the oil out of the barrel and avoid making a mess.
Let the oil drain out of the barrel, lifting the barrel eye end up if needed. Remove the barrel from the bench and secure the rod assembly for disassembly.  The piston nut is extremely tight and will require a hydraulic wrench (it is possible to crack the nut loose using another excavator, but it may result in a bent rod.
 
Remove the set screw that keeps the nut from backing off.  Depending on which series the cylinder is, there may be a ball under the set screw (there should have been one under this set screw, but it wasn’t there).
 
 
Do not forget this step or the rod threads and piston nut will be destroyed!!.
 
Torque the nut loose with the appropriate hydraulic wrench. Once the nut is cracked loose, it should spin right off, unless it is a nylock found on some machines.
 
Remove the nut, shim if used, piston, snubber sleeve and gland. If you do not have a new DU bushing to install in the gland, be careful the threads of the rod do not scuff the bushing up. Keeping the snubber sleeve in the gland will help.
 
 
Pick out the wear ring, rod seal, back up ring, buffer seal, buffer seal loader, oring and back up on the outside of the gland.  Remove the rod wiper by using a small prybar. Tap it in under the wiper, be careful not to gouge up the gland.  Using a wrench on the prybar, twist the wiper out.
 

 
If you have a new DU bushing, first check to see that the diameter and length are correct. Once your sure you have the right bushing, you can remove the old one, start by removing the snap ring that retains the bushing.
 
 
Using a bull nose chisel, work your way around the edge of the bushing to drive it out. Start on both sides of the split. Be absolutely certain that the chisel is not in the buffer seal groove!!!.  Be sure to have enough angle on the chisel that it bites into the bushing, but be careful that the chisel does not slip and gouge into the gland, or that the chisel does not pierce through the bushing and gouge into the gland.
 
 
Larger bushings may require ‘relieving’. Take a carbide burr and die grinder, and cut a groove down the length of the DU bushing on the side opposite the split. You need to cut as deep as possible, without damaging the gland. If you are careful while doing this, you can see a color change in the groove when you cut through the OD of the bushing. It takes patience, but once you get used to it, it’s pretty easy. You don’t want to cut all the way through for the entire length, as this old DU can be used on assembly for installing the new DU if you don’t have a tool and can’t machine one up. Try to drive the bushing out fairly straight if you need the old DU as a tool.
Pull the seals off the piston. The cap seal in the middle will be a little tricky. Watch the fingers, usually if you pierce the Teflon cap with a pick, you will be able to break the seal off when prying it off. Pick the seals loader out. Be careful not to gouge the seal groove up.
 
Click this link to take you to Part II of this series, Excavator Hydraulic Cylinder Seals and Inspection