Case 1835B Hydraulic Piston Seal Replacement.

I made a peg spanner for the gland and was able to remove it together with the piston rod and piston. I then undid the bolt retaining the piston and successfully replaced the seal and wiper in the gland.

The piston seal (ring) consists of an O ring in the bottom of the groove and above it an oblong cross section ring. I think this is called a "lathe cut piston ring". It is much harder than a normal O ring. The piston appears to be in one piece and I can see no way of splitting it to fit the ring. I am worried that if I stretch the ring over the piston it may break or retain its stretch preventing it entering the bore. I thought that if the ring stretched I could compress it with a piston ring compressor as if it were a metal pistion ring. However a trial fitting without the ring showed that the ring compressor wouldn"t fit inside the gland thread in the cylinder.

Is the piston splitable, or is there a "trick" to doing this job?

Thanks.

Graham.

There is a trick to it though if you decide to replace it. You replace the o-ring in the bottom of the groove first, of course. Then you stretch that plastic seal ring over the piston and get it into the groove. There are different ways to do this. Some people put the seal in hot water or oil- the idea is that the heat softens the seal and makes it easier to stretch over the piston. I usually work the seal around a little to soften it up, pull on it a little (but not too hard), then I stretch it over the piston. Once you get it in the groove, the ring will still be stretched out, and you won't be able to get the piston back in without cutting the ring. To shrink the ring back down, you can clamp it. I usually wrap the seal first with three or four layers of electric tape, then I wrap a strip of sandpaper around it- rough side away from the seal (cause it's handy- any heavy paper would do) . I then put a hose clamp (usually doubled up to be big enough to go around the piston) over the seal and tighten it moderately tight. The paper and the electric tape are important to keep the joint of the clamp from cutting into or deforming the seal. You let the seal stay clamped for maybe 20 minutes, and it'll stay that way. Make sure there are no burrs or sharp edges for the seal to catch on in the barrel of the cylinder- buff it smooth if you any- these plastic seals are easy to cut. Grease the seal and the barrel real good and tap it in with a plastic hammer- shouldn't take much force to get it in.

Now, when you take that clamp off, there'll probably be some slight deformation (indentions) from the clamp, even if you've wrapped it. So long as nothing has actually cut into the seal, it'll work fine.