TL;DR: A hydraulic cylinder reseal replaces only the soft parts, the seals, wipers and O-rings, and it is the right fix when a cylinder leaks but the rod and bore are still in good condition. A full rebuild goes further, stripping the cylinder completely so the bore can be honed, the rod re-chromed or replaced and every wearing part renewed, and it is needed when the metal surfaces are scored, pitted, corroded or bent. As a rule of thumb, reseal if a leak is the only fault and the hard parts measure within tolerance, rebuild if the rod or bore is damaged. Hydraulic & Engineering Services (HESL) carries out both, from a straightforward reseal through to a full strip, hone, re-chrome and rebuild, working to ISO 9001:2015 at its Strood workshop. Request a cylinder inspection here.
What is the difference between a hydraulic cylinder reseal and a rebuild?
A reseal and a rebuild are two different depths of the same repair. A reseal renews only the sealing elements inside the cylinder: the piston seal, rod seal, wiper, wear rings and static O-rings. The barrel, rod, piston and end caps are cleaned, inspected and refitted as they are. A rebuild is a complete overhaul: the cylinder is stripped to its bare components, the bore is honed back to a true finish, the rod is re-chromed or replaced, worn bushes and glands are renewed, and new seals go in as part of the job.
Put simply, a reseal fixes a cylinder that leaks but is otherwise sound. A rebuild restores a cylinder whose hard parts have worn or been damaged. Choosing correctly is the difference between a cylinder that runs for another five years and one that leaks again within weeks.
When is a reseal enough?
A reseal is the correct and most cost-effective repair when the fault is confined to the seals. Typical signs that a reseal will solve the problem include:
- External oil weeping from the rod as it extends and retracts.
- The cylinder creeping or drifting down under load when it should hold position.
- Slow or spongy operation caused by fluid bypassing a worn piston seal.
- A cylinder that has simply reached the end of normal seal life after years of duty.
The critical condition is that the metal is still good. If the rod chrome is unmarked, the bore is smooth and true, and there is no measurable bend or scoring, new seals alone will return the cylinder to full service. Contamination is often the reason seals fail early, so if you are resealing, it is worth checking the wider system. Our guide to common causes of hydraulic cylinder failure explains what typically destroys seals before their time.
When does a hydraulic cylinder need a full rebuild?
A reseal only buys time if the surfaces the seals run against are damaged. New seals pressed onto a scored rod or into a scratched bore will fail again quickly, because the fault was never the seal. A full rebuild is the right call when inspection finds any of the following:
- Scored, pitted or flaking chrome on the rod, which shreds the rod seal.
- A bent or misaligned rod, usually from side loading or an impact.
- A worn, oval or scored bore that lets the piston seal bypass.
- Worn gland bushes or bearing bands causing the rod to run off-centre.
- Corrosion on the rod or internal surfaces, common on marine, water-utility and outdoor plant.
In these cases the cylinder needs machining work, not just soft parts. HESL strips the unit, hones the bore, re-chromes or manufactures a new rod through its bar and tube division, and rebuilds the cylinder to original tolerances. If the underlying design keeps failing, the in-house team can re-engineer the weak point rather than rebuilding like for like. You can see the full scope of this work on the hydraulic cylinder repair and manufacture page.
How do you tell which repair you need?
You cannot always tell from the outside, because a leaking rod can hide either a simple seal fault or serious chrome damage underneath. A proper diagnosis follows a short sequence:
- Clean and inspect the exposed rod for score marks, pitting and corrosion.
- Check the rod for straightness, as a bend of even a fraction of a millimetre will wreck a new seal.
- Strip the cylinder and measure the bore for wear, ovality and scoring.
- Assess the gland, bushes and piston for wear.
- Decide: seals only if the metal passes, machining and rebuild if it does not.
This is exactly why HESL inspects before quoting rather than assuming. A cylinder booked in for a reseal sometimes reveals rod damage on strip-down, and it is far cheaper to catch that on the bench than to fit it, test it and find it leaking again.
Reseal vs full rebuild: a side-by-side comparison
| Factor | Reseal | Full rebuild |
|---|---|---|
| What is replaced | Seals, wipers, O-rings only | Seals plus honed bore, re-chromed or new rod, bushes and worn parts |
| Right when | Leak only, metal within tolerance | Rod or bore scored, pitted, corroded or bent |
| Machining needed | None | Bore honing, rod re-chrome or manufacture |
| Turnaround | Shorter, often a quick bench job | Longer, depends on machining and rod work |
| Cost | Lower | Higher, but far cheaper than a new cylinder |
| Service life restored | Full, if the diagnosis is right | Full, as good as a new unit |
Can I just fit a hydraulic cylinder seal kit myself?
For a simple cylinder on accessible plant, fitting a hydraulic cylinder seal kit is a reasonable in-house job, and HESL supplies seal kits, including Danfoss, as loose components through its trade counter. The risks to be aware of are two-fold. First, seals must be the correct size, material and profile for the pressure and fluid, so an approximate match will leak. Second, if the rod or bore is damaged and you fit seals anyway, you have spent time and money without fixing the fault. If the cylinder has done hard duty, or the rod shows any marking, an inspection is the safer route before you commit to a kit.
Reseal or rebuild: which is more cost-effective?
A reseal is cheaper on the day, but the cheapest repair is the one you only have to do once. Fitting seals to a worn rod is a false economy, because the labour to strip, seal, refit and test is largely the same whether the underlying metal is good or not. If that metal is damaged, you pay that labour twice. The genuinely cost-effective decision is to reseal when the hard parts are sound and to rebuild when they are not, which is why an honest inspection matters more than a headline price. Where a cylinder is obsolete, badly corroded or beyond economic rebuild, HESL can design and manufacture a replacement in-house, and our guide to hydraulic cylinder repair versus replacement sets out where that line falls.
The bottom line
Reseal when a cylinder leaks but the rod and bore are in good condition. Rebuild when the metal is scored, pitted, corroded or bent. If you are not sure which applies, that is the whole point of a workshop inspection: it removes the guesswork and stops you paying for the wrong repair. HESL repairs cylinders of all makes and models across industrial, mobile, marine, rail and waste sectors, holds seal kits in stock for fast turnaround, and works to ISO 9001:2015 and Achilles UVDB accreditation. Speak to an engineer about your cylinder here.
Frequently asked questions
What does a hydraulic cylinder reseal include? A reseal replaces the piston seal, rod seal, wiper, wear rings and static O-rings. The barrel, rod and piston are cleaned and inspected but not machined. It is the correct repair when the cylinder leaks but the metal surfaces are still within tolerance.
How do I know if my cylinder needs a rebuild instead of a reseal? If the rod is scored, pitted, corroded or bent, or the bore is worn, oval or scratched, new seals alone will fail quickly. Those faults need machining, honing and rod work, which is a full rebuild. The only reliable way to be sure is to strip and measure the cylinder.
How long does a reseal or rebuild take? A reseal is often a short bench job once the cylinder is on site. A rebuild takes longer because it may involve bore honing, rod re-chroming or manufacturing a new rod. Turnaround depends on parts and machining, which is why an early inspection helps you plan around downtime.
Why does my cylinder leak again soon after new seals? Almost always because the rod or bore was damaged and the seals were fitted anyway. The seal was never the root cause. A scored rod acts like a blade on the new rod seal, so the fix is to repair the metal, not to keep replacing seals.
Can you reseal or rebuild any make of cylinder? Yes. HESL repairs hydraulic cylinders of all makes and models, and where a unit is obsolete or beyond economic repair it can design and manufacture a replacement in-house through its cylinder and bar and tube divisions.
Do you supply seal kits on their own? Yes. Seal kits, including Danfoss, are available as loose components from the HESL trade counter in Strood for customers carrying out their own reseals.