i. Piston/Piston Rod

• - Check piston for signs of contact with barrel. This will happen if the barrel is out of round or the wear strip on the piston is worn. Extreme gland bushing wear can also cause piston/barrel contact at full extend.
• - Check clevis thread. If this is bent or cracked, the clevis is binding on the machinery and will cause severe rod and bushing side load. Look for pounded out metal at the clevis root.
• - Check piston seals for signs of bypassing. This would be seen as a smooth rippling along the sealing edge. A torn out look to the lip edge indicates cavitation from an over-running or negative load.
• - Check cushion sleeves for signs of contact with heads. Sleeves will contact head at full extension when the gland bushing is severely worn and/or side load is present. Blind end sleeve wear indicates the heads are out of square to the barrel or the piston nut is worn or not square to the piston.
• - Remove piston seal and check for metal particles or filing in the groove bottom. They will collect over time if the oil is contaminated
• - If the cylinder has been subjected to overheated oil, the seals will be brittle. The normally blue or orange color will be dark brown. O rings will be stiff and deformed.
• - If the piston was loose on the rod at the time of disassembly, , it may have deformation where the piston nut secured to the rod. If deformation is present, the piston should be scrapped. This is because the uneven surface under the piston nut will cause the nut thread to bend as it is tightened. This will cause the cushion sleeve to bend off the rod centerline.

ii. Gland Bushing Wear

Check for excessive gland bushing wear. This can be caused by:

• - Contaminated oil. Leaking cylinders will contaminate an oil system if the rod scraper allows debris into the cylinder upon retraction
• - Failure of the rod wiper. This will cause outside contamination to be drawn into the gland and past the bushing, causing rapid wear of both elements.
• - Side Load. Cylinders are structural elements only for loads applied along their axis. They are not meant to resist side load and will fail quickly under side load unless specifically designed for that purpose. Check the wear pattern on the bushing and compare it to the rod and tail mount. Often a side loaded bushing failure is matched by tail hold wear marks.
• - Incorrect bushing installation in head. Although normally not a common problem, if the bushing is not square in the head when front plate is assembled, the bushing may bind on the rod. This would happen if there were debris under the bushing lip during assembly.
• - Rod damage. Tools contacting the rod surface anywhere along the stroke can cause damage. This is common at the clevis end where the rod has been screwed into the clevis with improper tools. Any jaw mark or gouge will tear a seal immediately and cause leaks and wiper failure. This then allows more debris into the cylinder causing oil contamination and bushing wear.
• - Paint. Check for over-spray on the rod if the area was recently painted. This can happen on new and rebuilt equipment or from sloppy painting nearby. The rod scraper will not remove paint and will cause seal/scraper failure.
• - Excessive line length. On rare occasions, contamination will build up in the cylinder because the line volume between the cylinder and the valve exceeds the cylinder displaced volume. This causes the same volume of oil to shuttle back and forth between the valve and the cylinder, but never get through the valve to be returned to tank for filtering.

iii. Gland Bushing Inspection

• - Check spiral oil groove as a wear indicator. Severe wear will show as a high polish on one side will obvious out of round to the bore. Bushings with excess of .010” radial wear should be scraped. Excessive bushing wear causes local seal compression and deformation, feathering of the seal lip and heal leading to blow out. Bushing wear also causes the cushion to enter the gland end head off center, which will cause metal to metal contact. This will introduce metal particles into the system.
• - Check for a rippled edge to the seal. This indicates the seal is leaking at a point on the edge, which causes rapid erosion of the lip edge.
• - A torn seal indicates a rough spot on the rod or improper assembly during the last rebuild.
• - Seal components should be pliable and near to original color.

iv. Barrel

• - Check barrel for axial grooves caused by piston scraping.
• - Barrels usually have a long life if the cylinders are free of foreign particles.
• - Minor scratches up to .010” deep can be honed out by a qualified honing shop.
• - Dented or exterior worn barrels must be scrapped. Even if the dent can be straightened out, it is now a potential failure point under pressure. A barrel with wear on the outside will eventually fail due to metal fatigue in the roots of the scratches.

v. Heads

• - Check heads for port damage and damaged retaining plates.
• - Check heads for internal face damage. This would indicate the piston is slamming into the head due to poor cushioning or excessive load.
• - Check for oversize or elongated mounting holes.

i. General

• - Seals should be replaced if there is any doubt about their condition. This is one of the least expensive spares to change in the cylinder If the cylinder has been in continuous service over 3 months, the seals should always be changed.
• - NEVER, NEVER, NEVER use WD40 or similar volatile solvent (CRC) on urethane seals during re-assembly. Urethane absorbs WD40 and will cause swelling and rapid failure if used.
• - ALWAYS use clean hydraulic oil to ease seals into place during assembly.
• - Use blunt tools that will not scratch or tear seals. A slotted screwdriver can ruin a piston or gland seal. Modified plastic paint brush handles work well for easing seals into place.
• - Check piston for wear on o.d. and seal grooves. Seals can slowly wear grooves out of shape to the point that proper sealing is no longer possible. The piston faces where the nut and rod seats should also be flat and true. Unevenness here will cause nut and rod failure.
• - Always Use Factory Tie rods and New Tie Rod nuts. Factory tie rods are made of high strength steel that are made to be tensioned without deformation. Use of other materials poses a risk of tie rod failure, machine damage and personal injury.
• - DO NOT RE USE OLD TIE ROD NUTS. These nuts as supplied from the factory are single use nuts that have a built in nylon locking ring. The locking performance of these nuts are greatly reduced when used a second time as nylon has already been deformed.

ii. Procedure.

A CLEAN WORK AREA IS CRITICAL TO SUCCESSFUL CYLINDER REBUILDS

• - Replace all seals for the piston, gland, and heads.
• - If the clevis threads are of smaller o.d. than the rod, then the piston can go onto the rod directly.
• - If the clevis threads are full diameter, then the gland bushing (already fitted into the head) must be installed from THE PISTON END OF THE ROD so as not to cut the gland bushing rod seals on the rod end threads.
• - Fit piston nut to rod and torque to the value listed in the attached table. Proper torque of the piston nut is essential to ensure the piston does not loosen in service.
• - Stand barrel vertically on a bench without heads.
• - Lubricate the piston and barrel top edge. Slide the piston/rod assembly into the top of the barrel in a rocking motion. This will ease the seals past the lip of the barrel.
• - Watch out for seal lip folding as the last of the seal passes the lip. Use a blunt tool (plastic or brass) to push the lip past the barrel edge.
• - Slide on the gland end head with gland bushing pre-fitted.
• - Lay assembly horizontal on bench and fit blind end head.
• - Align ports, fit front plate and install tie rods. Be sure rod is fully retracted into the cylinder before tie rods are tightened. This reduces the tendency to pull the heads off-square with the barrel.
• - Tighten tie rods in criss-cross pattern to ensure the heads are pulled straight onto the barrel ends.
• - See attached table for tie rod torque specifications.
• - Pressure test for leaks and binding of rod.
• - Fit ports with plastic port plugs when finished.

i. Needle Valve Setting

• - Adjust the needle valve to sufficient enough to eliminate hard contact of the piston to the heads.
• - Excessive cushioning caused extreme pressures to build up in the cylinder that add extra strain on the seals.
• - A good starting point for the needle valve position is screw the needle valve all the way in until it is hand snug. then back off ½ to 5/8 of a turn.

ii. Remounting on machinery

• - Check mounting brackets on machinery for wear and cracks. Worn pins and mounts create slop that applies shock loads to the cylinder during operation. Shock loads from worn parts are 2 to 3 times as large as the normal cylinder forces. This repeated pounding also eventually causes metal failure in the machine frame, broken welds and spider cracks forming in the frames.
• - Re check cylinder alignment. Even moderate misalignment will cause rapid wear of new gland bushings and seals.
• - Trunnion mounted cylinders have zero lateral flexibility and therefore must be aligned very carefully. Both extension and retraction positions should be checked. If the connected load pivot is not parallel to the trunnion centerline, the cylinder will be pushed side to side through its stroke. This will rapidly break the trunnion mounts or pins.
• - Cylinders under no circumstance can be used as machine guide mechanisms. All external guide loads must be taken by the machine mechanism. All loads seen by the cylinder must axial to the cylinder. The cylinder cannot withstand side loads or bending moments applied to rod end or cylinder body.
• - Check that the rod clevis does not bind at full extension or retraction.
• - Always keep ports plugs in place until hose connections are made.