What “overhaul” actually covers
The word is used loosely. A buyer comparing two quotations, or a manager approving a repair budget, needs to know which of these is meant:
| Scope | Typical content | What it is not |
|---|---|---|
| Package overhaul | Airend, motor or engine, coolers, valves, hoses, controls and sensors reviewed and restored as found necessary | A guarantee that every component is new |
| Airend rebuild | Bearings, seals and gears replaced, rotors and housings inspected and measured, clearances set | A full package overhaul if the rest of the machine is untouched |
| Airend exchange | A rebuilt or new airend fitted in place of the old one | An overhaul of the original airend |
| Reciprocating overhaul | Valves, rings, pistons, liners, bearings and coolers inspected, replaced or reconditioned | A screw-airend style rebuild |
| Engine overhaul (portable diesel) | Engine top or major overhaul to the engine maker’s method | Work on the compressor airend |
| Dryer overhaul | Refrigeration circuit, valves, desiccant or drains restored | Work on the compressor |
The work order controls the scope. The record lists what was included, what was excluded, what was replaced with new parts, what was reconditioned and what work, if any, was carried out by a specialist outside our workshop.
Before dismantling: the as-found record
An overhaul record is only as good as its starting point. Before dismantling we record:
- Machine identity: make, model, serial number, technology and nameplate rating.
- Running hours, loaded hours where available, and the date of the last major service.
- The reason for the overhaul: noise, vibration, high temperature, low capacity, oil carry-over, a seized airend, or planned hours.
- Operating readings if the machine can still run: discharge pressure and temperature, motor current, load and unload behaviour, oil consumption.
- Alarm history from the controller.
- Photos of the package, nameplate and any visible damage or leaks.
Old readings without dates or known instruments are useful as background but are not treated as a measured baseline.
Dismantling findings
As the machine is opened, each finding is recorded with a photo and, where relevant, a measurement. In a rotary screw airend that typically includes:
- Bearing condition: spalling, discolouration, cage damage, axial play.
- Rotor condition: contact marks, coating wear, scoring, corrosion from water in the oil.
- Housing bores: wear or contact marks.
- Shaft seals: leakage paths and wear on the running surface.
- Drive gears or coupling: tooth wear and alignment.
- Oil condition and deposits: varnish, sludge, water, metal particles.
Findings explain the cause. Water-damaged bearings point to oil running too cool or poor drainage; varnish points to high temperatures or extended oil life; contact marks on rotors point to bearing failure or wrong clearances. A record that explains the cause helps prevent a repeat failure. Our airend failure modes and airend inspection and measurement pages cover this in depth.
Disposition of each part
Every significant part is given a decision and a reason:
- Reuse: within the maker’s limits on inspection or measurement.
- Recondition: restored by machining, cleaning or another process; specialist processes such as rotor regrinding or coating are arranged where needed.
- Replace: worn beyond limits, damaged, or a part that is always replaced at overhaul, such as bearings, seals and gaskets.
The record states whether replacement parts are genuine maker’s parts or named aftermarket parts, so the customer can make an informed choice. Parts are identified from the make, model, serial number, nameplate photo or the old part, and fit is confirmed before quoting.
Reassembly checks
Reassembly follows the maker’s procedure where it is available. The record notes cleanliness of parts and work area, bearing fits, end float and rotor clearances where they are set, gear backlash, seal installation, fastener tightening to the maker’s values, and alignment of motor and coupling. Values are recorded as measured; we do not write in tolerances from memory.
Outside the airend, the overhaul usually also covers the separator element, oil and air filters, minimum pressure valve, thermostatic valve, inlet valve, oil cooler and aftercooler cleaning, hoses and sensors. Each is recorded as checked, replaced or not in scope.
As-left testing
The test after overhaul is what turns a repair into a verified result. A practical test sheet includes:
| Check | Why it matters |
|---|---|
| Run unloaded, then loaded in steps | Confirms smooth running and no abnormal noise |
| Discharge pressure and load and unload points | Confirms the machine reaches and holds its set pressures |
| Discharge temperature, normally about 75–95 °C for an oil-injected screw | Confirms cooling and oil circuit are working |
| Motor current at load compared with nameplate | Shows the airend is not dragging and the motor is healthy |
| Vibration and bearing temperature, where measured | Gives a baseline for future condition monitoring |
| Oil carry-over check after running in | Confirms separator and minimum pressure valve function |
| Safety trips tested where the maker’s procedure allows | Confirms protection works after reassembly |
| Free air delivery test, if agreed | The only way to show capacity has been restored |
If a flow test was not carried out, the record says so, and it does not claim that rated capacity has been restored. See our post-rebuild validation page for the test method.
Why overhauled machines fail again
A second failure soon after an overhaul usually has a cause outside the airend. The record should show that these were checked:
- Oil temperature too low: a stuck thermostatic valve or oversized cooler lets moisture condense in the oil, damaging new bearings.
- Oil temperature too high: fouled coolers, a hot compressor room or recirculating exhaust air break down the oil and cause trips, especially in an Indian summer.
- Dust: damaged intake ducting or a poor air filter lets abrasive dust into the airend.
- Wrong oil or mixed oils: incompatible lubricants can form varnish and deposits.
- Drive problems: misalignment, worn couplings or belt tension errors load the bearings.
- Short cycling: frequent load and unload cycles from poor control settings or an undersized receiver.
For portable diesel machines, the engine side adds its own causes: blocked radiators, poor fuel quality, worn engine air filters and safety shutdowns on high coolant temperature or low engine oil pressure. An overhaul that fixes the airend but ignores these will not last. That is why we record the condition of the whole package, not only the part that failed, and give the customer a clear list of anything outside the agreed scope that needs attention.
Overhaul, exchange or replace?
Not every tired machine should be overhauled. The decision depends on the condition found, parts availability, the machine’s age and technology, its energy use and how critical it is to the plant. A machine with high specific power or one that is badly oversized for today’s demand may be better replaced, even if it can be repaired. Our overhaul versus replacement decision tool and rebuild, exchange or replacement page help with that decision.
Maintenance evidence from fleet work
Our own rental fleet gives us steady overhaul experience. On hire jobs we change oil and service every 300 running hours, and those logs show how service intervals, dust and heat affect wear. That experience feeds directly into how we inspect and record customer machines.
How Reddy Compressors helps
Reddy Compressors, at Tarnaka, Secunderabad, has served industry since 2002 as an independent multi-brand business. We are not an authorised dealer of any brand and do not claim factory authorisation. We have tie-ups with all major and reputed brands. For overhauls we:
- Overhaul rotary screw, reciprocating and portable diesel compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Sullair, Doosan, Kirloskar, Gardner Denver and others.
- Support airend rebuilds and exchanges, arranging specialist processes where needed.
- Supply genuine and named aftermarket spares across India, with fit confirmed before quoting.
- Provide rental compressors from our own fleet while your machine is in overhaul.
- Follow up with service and AMC through our team of over 20 service engineers and technicians across Telangana and Andhra Pradesh.
- Supply used and refurbished compressors where replacement is the better choice.
What to send us
- Make, model, serial number and nameplate photo.
- Running hours and the date of the last major service.
- The symptoms or reason for the overhaul, with any alarm codes.
- Recent readings: pressure, temperature, current, oil consumption.
- Whether you need temporary air during the work.
- Site location.
Frequently asked questions
When does a screw compressor need an airend overhaul?
Signs include rising bearing noise or vibration, increasing discharge temperature, falling capacity, higher motor current for the same output and oil leaks at the shaft seal. Many makers also recommend an overhaul at set running hours. Condition checks and oil analysis help decide whether to overhaul early or continue running safely.
What is included in a compressor overhaul?
It depends on the agreed scope. A typical screw package overhaul covers bearings, seals and gaskets in the airend, inspection of rotors and housings, the separator element, filters, valves, coolers, hoses and sensors, followed by reassembly and a test run. The work order should list inclusions, exclusions and any specialist work.
Does an overhaul restore my compressor to its original capacity?
It can, but only a free air delivery test after the overhaul proves it. Worn rotors or housings that are reused within limits may still leave some loss of capacity. A good overhaul record states whether a flow test was carried out and, if not, does not claim that original capacity has been restored.
Is it better to overhaul or replace an old compressor?
Compare the overhaul cost with the condition found, parts availability, energy use and how well the machine suits today’s demand. An old, oversized or inefficient machine may cost more to run than a new or good used one. We help you compare options using measured readings rather than age alone.
Do you use genuine parts for overhauls?
We supply both genuine maker’s parts and named aftermarket parts, and the quote and record state which were used. We identify parts from the make, model, serial number, nameplate photo or old part, and confirm fit before quoting. Where warranty conditions apply, check the maker’s requirements on parts before deciding.
Can you supply a compressor while mine is being overhauled?
Yes. We rent diesel and electric compressors from 50 to 2,000 cfm and 2 to 30 bar from our own fleet, with hoses and treatment where needed. Planning the rental before the machine is opened avoids a gap in air supply if the overhaul takes longer because of findings.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.