Excavator Hydraulic Cylinder Seals and Inspection

Start inspection with the rod.  Measure the cylinder rod diameter with a micrometer, checking over the entire length and at various spots around  the diameter. You’re looking for low spots. A low spot that you can’t see may exist from previous rod repairs.  Check the rod for pits, dents, dings, or scratches, if they are present, the rod will need repairing or re-chroming. Excavator cylinder rods are often nickel plated, then chrome plated over nickel. If the rod requires re-chroming it is stripped in a strip tank, however the nickel will not strip of electrically, so it must be mechanically removed.  You don’t need to worry about this as the rod will have to go out to a chrome shop. I’ll save the chroming info for another posting.
 Roll the rod on rollers or V blocks, and with a dial indicator check for run-out indicating a bent rod.  If it is bent, it will need straightening. If the rod needs re-chroming, get the rod straightened at the same time. Chrome work is usually charged by the square inch and can be anywhere from $.50 to $1.00 per square inch.  Measure the diameter in inches, multiply by PI (3.1416) then multiply by the chrome length, then by the price per square inches. In this case it was 80mm / 25.4 = 3.1496 inches, multiply by 3.1416 = 9.895 inches, multiply by length of 40″ = 395.79, multiplied by $.70 equals $277.05. Please note some shops have minimum charges, and if your rod requires extensive repairs, the job will cost more.
 Before sending your rod out, remove the pin wipers from the rod eye, grease fitting and remove grease from the rod eye and check the rod bushing condition and determine if this is to be replaced. If there are plastic rings on the rods stub, under the snubber rings on either side of the piston, save these rings, they will be re-used unless broken. They do not come in a seal kit, and usually have to be ordered through the OEM. Measure the pin eye wipers, they are ordered by ID, OD, and height. These ones were 71×86x5  W071086050WS
 Now inspect the barrel condition. Look for internal scores or bulging. The barrel will hopefully have its original burnished finish. This finish is achieved with a head consisting of burnishing rollers; it should have a black mirror look to it.  If there is no damage in the barrel, do not hone it, the burnished finish is much better than any finish you can get with a hone. Measure the barrel internal diameter where the gland seals in the barrel, referred to as the gland seat. Clearance here should not exceed .009″ Remove the pin eye wipers, they are ordered by id, OD, height.  Replace the eye bushing if required. These wipers were 65×80x5 W065080050WS
Measure the diameter of the piston wear band groove that has the phenolic wear bands (the two closest to the piston seal). Add twice the cross section of the wearband (2.5mm) to the wear band diameter. This size should be around .006″ smaller than the bore and not to exceed .011″. Phenolic wear bands are ordered by OD, cross section, and height, or ID, OD, Height. These ones were 110×115x8 or G115110080GC.
 
The Teflon wear bands, even though referred to as wear bands are in fact wipers. The wipers take advantage of Teflon’s tendency to absorb contamination and draw it away from the walls of the barrel.  Teflon has very little compressive strength and would not have much benefit as a true wearband. Measure the cross section of the wear band, usually 4mm, the bore size you know, measure the groove height. These wear bands are often ordered in strips, so convert the diameter to a circumference and order 2 lengths plus a little bit extra.  These ones were 4mm cross section, 6mm tall. The wear strip in this case is WS0060040/CG and two 14 ¼” strips were required.
 
Piston seals come in lots of different cross sections and heights.  Make note of the seal style, in this case it is a two piece with a loader and a Teflon cap. Measure the seal groove diameter, the bore size you know, measure the groove height. This particular seal was a P115094081P2B
 
 
Now for the gland. As mentioned previously, do not remove the DU bushing until you have a replacement. What you need to know to order the new one is the rod diameter and the height of the DU bushing, in this case it was 80mmx30mm. GMB8030DU
Check the buffer seal and rod seal groove for rust, if rusty, polish up with a fine grit flapper wheel. If the rust is severe, have a machine shop take a very light cut out of the seal groove. Take a maximum of .010″ above the original diameter. If you want a super duty cylinder, order a custom made rod seal backup machined out of hard nylon. Order the id .003″ larger than the rod diameter, order the OD .002″ smaller than the seal groove diameter. Make the height the same as the old back up, order this with NO split. Be sure to install the backup when the time comes, before the rod seal. You may need to soak it in hot water first. BU080095100RA. Specify NOK rod seals, do not use SJ seals. They are also ordered by ID, OD, and height. R080095090RA.
Measure the diameter of the buffer seal groove. A set of bent inside calipers are usually required for this, and it takes a sensitive feel. You need to use the calipers like you would with an inside micrometer, adjusting until a very light drag is felt. It takes a bit of practice to get consistent sizes.  In this case the diameter was 3.759” or 95.5mm. It was a solid Teflon cap with a square loader, it will be replaced with a lip type buffer R80095060RH-1


 
Between the rod seal and rod wiper may be another Teflon wear band, although like the Teflon wear bands on the piston, this is also actually more of a wiper than a wear band. It is supposed to catch any contamination that made its way past the rod wiper. Flap this groove up as well if rusty; don’t worry about getting all of the pitting out if present, just the loose rust, the important thing is that it clean.  This wear band is ordered as a strip. 10 ½” of WS0097025/BR60 was required. The rod wiper- Give this groove a light polishing as we will use a small amount of bearing retainer to form a seal on the outside of the wiper, this prevents water from getting around the wiper, especially problematic on boom lift cylinders. ** Only use retaining compound on wipers with metal cases, do not get any on the rubber portion of the wiper as they will deteriorate. The wiper is ordered by ID, OD, and height. W080094080WR
 
Measure the cross section of the oring and backup on the outside of the gland, they are not the same cross section. The cross section of the oring is always heavier than the back up ring. There should be no crush on the backup ring, just the oring. JIS, or Japanese Industrial Standard orings are always an odd cross section. Instead of 3mm, it will be 3.1mm. The groove diameter is the same as for a 3mm, but there is extra crush provided on the 3.1.  Do not use a 3mm.  If you want to build a super duty cylinder, have a custom backup machined out of hard nylon.  Make the id of the backup .003″ bigger than the groove diameter, make the OD .003 bigger than the gland seat diameter of the barrel. Then scarf cut the backup ring so that the joint overlaps at an angle.  Use a razor, the .003″ extra on the OD and ID should allow for the kerf in cutting.  Put the back up in the groove and trim if necessary with a bench grinder. If the backup is small in cross section relative to the bore size, like the 2.5mm cross section in this example with a 115mm bore, you can sometimes install the back-up ring without splitting it. The oring and backup in this example are: MOR1094031/NBR90 &  BU110115012SD/T
 Order any orings required for fittings or flow tubes and extra pin eye wipers for the link arms if required. The next step is prepping the parts for assembly.
 Rod Wiper – W080094080WR
Gland wear strip – ½” of WS0097025/BR60
Rod seal BU – BU080095100RA
Rod seal – R080095090RA
Rod Buffer – R80095060RH-1
DU Bushing – GMB8030DU
Gland oring – MOR1094031/NBR90
Gland BU – BU110115012SD/T
Piston wear strip – two 14 ¼” strips WS0060040/CG
Phenolic wear bands – two G115110080GC
Piston seal – P115094081P2B
Rod Pin Wipers – W071086050WS
Barrel Pin Wipers – W065080050WS
Find all of your seal needs here: http://sealsonline.com/website/light_page.asp?code=homepage
Next post will be prep and assembly.