A cylinder comes off the machine because it is leaking, drifting or knocking. Those three symptoms lead to three very different jobs, and which one you are buying is not knowable until the unit is stripped and measured. Quoting before that point is guesswork, and a quote given without a strip-down is usually the one that changes later.
This is the decision tree an engineer actually runs, and what pushes a job from one branch to the next.
Branch one: seals and wear rings only
This is the cheapest outcome and the most common hope. It is the right answer when the rod and the bore are both within limits and the only failed items are elastomeric — rod seal, piston seal, wiper, O-rings, and the bearing or wear rings that keep metal off metal.
The tell is what the seals look like when they come out. Seals that are worn evenly and have simply hardened have reached the end of a normal life, especially in Eastern Province ambient temperatures where the fluid runs hot all summer. Seals that are cut, extruded into a spiral, or nibbled at the edge have failed because of something else. Fitting a new kit against an unresolved cause buys a few weeks.
The three usual causes: contamination scoring the sealing surface, a bore or rod that is out of tolerance so the seal is being asked to close a gap it was never designed for, and a pressure spike above the seal's rating. The first is a system problem, not a cylinder problem, and it will destroy the new kit too if the fluid is not cleaned up.
Branch two: the rod
The rod is inspected for three things, and each has a different consequence.
Chrome condition. Surface pitting that a fingernail does not catch will usually run. Pitting deep enough to catch is a leak path, because the rod seal has to ride across it on every stroke. Flaking chrome is worse than pitting: once the plating starts lifting, the loose edge acts like a blade on the seal lip, and the area under it is already corroding.
Straightness. Measured on rollers or between centres over the rod's length. A bent rod loads the gland bush on one side, which is why a cylinder that has been struck or side-loaded often comes back with the gland worn oval and a leak that reappears within days of a reseal.
Diameter. A rod that has worn undersize will not seal reliably regardless of how new the kit is.
Where the chrome has failed but the base metal is sound, re-chroming is an option: the rod is ground undersize, plated back, and ground to finish. That is a real repair with a real lead time, and it is the point at which a job stops being a same-week turnaround. Where the base metal is pitted through, corroded under the plating, or the rod is bent beyond correction, a new rod is the honest answer.
Branch three: the bore
The tube is checked for ovality, for scoring depth, and for distortion around the welds at the cap and gland ends.
Light scoring hones out. Honing removes material, so a bore that is already near its limit cannot absorb much of it — and every pass makes the piston seal's job harder. Ovality is the more serious finding, because a bore that is no longer round cannot be honed round again without going oversize, and an oversize bore needs an oversize piston seal that may not exist for that profile.
Distortion at the weld is the one that ends the conversation. A tube that has been overheated, over-pressurised or repaired badly in the past can be out of shape near the cap, and that region is not something a hone reaches usefully.
Where a rebuild stops being worth it
Three findings usually mean a new cylinder is cheaper than repairing the old one, and it is worth knowing them before you pay for a strip-down:
- The seal profile is obsolete. Older or proprietary cylinders sometimes use a piston seal geometry that is no longer manufactured. A close substitute that does not match the groove is not a repair, it is a return visit.
- The tube will not clean up. Once honing to remove scoring would take the bore past its limit, there is nothing left to save.
- The mountings are obsolete or damaged. A cracked or elongated clevis, a damaged trunnion, or a mounting pattern nobody makes any more can cost more to reproduce than the rest of the cylinder is worth — although reproducing it is sometimes exactly the right answer when the machine itself is obsolete and the alternative is scrapping it.
What decides the cost, since nobody will quote you a number honestly
Cylinder repair prices are not comparable between jobs, and any figure quoted before strip-down is a placeholder. What actually moves the cost:
- Whether the rod needs re-chroming or replacing — this is usually the single biggest step change.
- Whether the seal kit is a standard profile held as stock or has to be sourced or made up from individual items.
- Bore work: honing is modest, re-tubing is not.
- Whether the cylinder must be tested after assembly, and to what.
- Whether the unit is stripped in a workshop or the work has to be done on site under permit, which changes the labour picture entirely.
The useful thing to ask a repairer is not "what does a cylinder repair cost" but "what will you report back after strip-down, and will you quote the rebuild before starting it". A findings report that names the rod condition, bore condition, gland wear and the seals fitted is the difference between a repair and a gamble.
What to send with the cylinder
A repair moves faster when it arrives with its context. Useful: the machine and application, the symptom in the operator's words, the working pressure, the fluid type, whether the cylinder has been repaired before, and photographs of the mountings and the rod end before it is removed. A nameplate photograph is worth more than a description — bore, stroke and rod diameter are usually on it.
If the mountings are unusual or the unit is off an obsolete machine, say so at the enquiry stage rather than after strip-down. That is the case where reproducing a cylinder to drawing is often the only route, and it needs a different conversation.
We strip, inspect and report before any rebuild is quoted, and we reproduce cylinders where the original is obsolete. See Cylinder Repair & Reseal, or send the nameplate and a photograph of the rod through our contact form and we will tell you which of the three branches you are probably on.
Updated 7 September 2026