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What Are Oilite Bearings?
"Oilite" is an example of a trademark that became a generic descriptor, much like "Kleenex" for facial tissues. In engineering procurement and design discussions, "Oilite bearing" is widely understood to mean a sintered bronze, oil-impregnated bushing—regardless of the specific manufacturer.
These bearings are produced by compacting bronze powder (typically copper-tin, Cu-Sn) into a cylindrical or custom-shaped die, sintering the compact to bond the powder particles while preserving interconnected porosity, and then vacuum-impregnating the porous matrix with lubricating oil. The result is a bearing that carries its own lubricant supply and replenishes the running surface automatically during operation.
SinterWorks PM produces Oilite-type bearings in standard and custom dimensions. See our oil-impregnated bearings page for the broader product family, including iron-based and iron-copper variants.
SAE 841 and MPIF CT-1000-K26 Specifications
Oilite bearings are most commonly specified against two standards that describe chemistry, density, and minimum oil content.
SAE 841 is a Society of Automotive Engineers standard for sintered bronze bearings. It defines a copper-tin bronze with nominal 10% tin content, minimum density of 6.4 g/cm³, and minimum oil content of 18% by volume. The standard ensures interchangeability among suppliers and predictable performance in automotive and industrial applications.
MPIF CT-1000-K26 is the Metal Powder Industries Federation designation for a material that is functionally equivalent to SAE 841. The "CT" prefix indicates a copper-tin material, "1000" denotes the nominal tin content, and "K26" specifies the minimum strength class and oil impregnation requirement.
| Property | SAE 841 | MPIF CT-1000-K26 |
|---|---|---|
| Nominal chemistry | Cu-Sn (approx. 90/10) | Cu-Sn (approx. 90/10) |
| Minimum density | 6.4 g/cm³ | 6.4 g/cm³ |
| Typical density range | 6.4–7.2 g/cm³ | 6.4–7.2 g/cm³ |
| Minimum oil content | 18% by volume | 18% by volume |
| Typical oil content | 18–25% by volume | 18–25% by volume |
| Typical hardness | HRB 35–60 | HRB 35–60 |
| Minimum yield strength (K26) | Not specified | 125 MPa |
These values are representative. Actual performance depends on powder grade, compaction parameters, sintering conditions, and oil type. SinterWorks PM verifies oil content by weight-gain testing and dimensional inspection per customer requirements.
How Oilite Bearings Work
The self-lubricating mechanism of an Oilite bearing depends on controlled porosity and capillary action.
Manufacturing: Bronze powder is pressed to a density that leaves 10–20% interconnected porosity. After sintering, the bearing is placed in a vacuum chamber where air is removed from the pores. It is then immersed in oil, and atmospheric pressure forces oil into the evacuated pore network. Typical oil content is 18–25% by volume.
During operation: Shaft rotation generates heat and friction at the bearing surface. The oil expands and is drawn from the pores to the surface, forming a thin lubricating film that prevents metal-to-metal contact.
At rest: As the bearing cools, surface tension and capillary action draw the oil back into the porous matrix. The bearing recharges itself without external lubrication.
This cycle repeats continuously until the oil eventually degrades or depletes over very long service intervals. Under typical light-to-moderate loads, Oilite bearings can operate maintenance-free for 50,000–150,000 cycles or more.
Oilite Bearings vs Solid Bronze Bushings
Buyers sometimes confuse Oilite bearings with solid bronze bushings. The two are different in structure, performance, and application fit.
| Attribute | Oilite Bearing (Sintered, Oil-Impregnated) | Solid Bronze Bushing (Machined, Dense) |
|---|---|---|
| Structure | Porous (18–22% voids), oil-filled | Fully dense, no porosity |
| Lubrication | Self-lubricating via oil film | Boundary lubrication (leaded grades) or external lube required |
| Load capacity (PV) | Typically 0.8–3.5 MPa·m/s | Typically 2.0–10+ MPa·m/s |
| Max continuous temperature | ~80–120°C (standard oil) | ~150–250°C (alloy dependent) |
| Maintenance | Maintenance-free for designed life | May require periodic re-lubrication |
| Cost at volume | Lower; suited to high-volume PM production | Higher; machining intensive |
| Typical applications | Motors, fans, appliances, light automation | Heavy machinery, hydraulic cylinders, high-load pivots |
For a deeper comparison, see our oil-impregnated bearings vs bronze bushings guide.
Typical Applications
Oilite bearings are the default choice for light-to-moderate duty applications where maintenance access is difficult or undesirable.
Automotive auxiliaries: Wiper linkage pivot bushings, power window regulator guides, seat adjustment mechanism bearings, and HVAC blower motor supports. The maintenance-free character is essential for components enclosed in door panels and dashboards.
Home appliances: Washing machine agitator bearings, refrigerator compressor supports, dishwasher pump bushings, and vacuum cleaner motor mounts. Long life without re-lubrication improves product reliability ratings.
Electric motors and fans: Small motor shaft bearings, ceiling fan supports, and ventilation equipment. Oilite bearings run quietly and do not require grease fittings.
Office equipment: Printer paper-feed roller bushings, copier carriage guides, and shredder mechanism bearings.
Light industrial: Conveyor idler rollers, packaging machinery pivots, and actuator slide bearings. See our bronze self-lubricating bearings page for additional application examples and material guidance.
Design and Installation Guidelines
Proper design and installation are essential to achieve the rated life of an Oilite bearing.
PV limit: The product of bearing pressure (MPa) and sliding velocity (m/s) must remain within the bearing's capability. Standard Oilite bearings in SAE 841 typically operate at PV values up to 3.5 MPa·m/s with adequate heat dissipation. Exceeding this limit causes overheating, oil breakdown, and premature wear.
Shaft clearance: A running clearance of 0.015–0.040 mm is typical for shaft diameters under 25 mm, increasing slightly for larger bores. Too little clearance restricts oil film formation; too much causes vibration and noise.
Housing fit: Oilite bearings are usually installed with a press fit into a steel or aluminum housing. The recommended interference is typically 0.5–1.0% of the bearing outer diameter. The housing bore should be clean, chamfered, and free of burrs to prevent damaging the bearing edge during insertion.
Shaft surface finish: A shaft surface roughness of Ra 0.4–1.6 µm is recommended. Smooth shafts reduce wear and help maintain the oil film. Hardened steel shafts (minimum 200 HV) are preferred for longer life.
Environmental protection: In dusty or abrasive environments, a seal or shield should protect the bearing interface. Abrasive particles can embed in the porous surface and accelerate shaft wear.
Quality Verification
SinterWorks PM verifies Oilite bearing quality through dimensional inspection of bore, OD, and length; oil-content measurement by weight gain; and hardness testing on production samples. Material chemistry is checked against incoming powder lot certificates to ensure conformity with SAE 841 and MPIF CT-1000-K26 requirements. For automotive and industrial programs, Certificates of Conformance and inspection reports are available per shipment. See our quality inspection process for detailed capability.
Maintenance and Re-Impregnation
Under normal operating conditions within rated PV and temperature limits, Oilite bearings require no maintenance. The oil supply is designed to last the service life of the assembly.
Signs of oil depletion: Increased noise, higher friction, visible discoloration from overheating, or measurable bore wear indicate that the oil has degraded or depleted. In most consumer and automotive applications, the bearing is replaced as a wear item rather than re-impregnated.
Re-impregnation: For large or expensive bearings, re-impregnation is possible. The bearing is cleaned in solvent to remove degraded oil and contaminants, dried, and then vacuum-impregnated with fresh oil of the correct viscosity. Re-impregnation does not restore material lost to wear, so it is only viable if the bore and OD are still within tolerance.
Oil selection: Standard bearings are impregnated with SAE 30 mineral oil for general-purpose use. Synthetic oils extend temperature range and oxidation resistance. Food-grade oils are available for applications requiring FDA compliance.
Request an Oilite Bearing Quote
If you are specifying Oilite bearings for a new design or seeking a replacement supplier, send us your requirements. Useful information includes bore diameter, OD, length, load and speed conditions, operating temperature, and any standard specifications (SAE 841, MPIF CT-1000-K26, or equivalent).
SinterWorks PM produces sintered bronze oil-impregnated bearings in standard and custom dimensions. We review designs for PV rating, housing fit, and shaft compatibility, and provide quotations covering tooling, unit pricing, and sample schedules.
Frequently Asked Questions
Q: What is an Oilite bearing?
A: An Oilite bearing is a sintered bronze bushing with interconnected porosity that is vacuum-impregnated with lubricating oil. The name began as a brand but is now used generically in industry to describe this type of self-lubricating powder metallurgy bearing. It operates maintenance-free by drawing oil from its internal pores to the bearing surface during use.
Q: What does SAE 841 mean?
A: SAE 841 is a Society of Automotive Engineers standard for sintered bronze bearings. It specifies a copper-tin bronze composition, minimum density of 6.4 g/cm³, and minimum oil content of 18% by volume. Bearings meeting SAE 841 are interchangeable across suppliers and are widely used in automotive and industrial applications.
Q: What is MPIF CT-1000-K26?
A: MPIF CT-1000-K26 is the Metal Powder Industries Federation material designation for a copper-tin bearing bronze that is functionally equivalent to SAE 841. CT indicates copper-tin, 1000 denotes the nominal alloy grade, and K26 specifies the strength and oil-content class.
Q: How long do Oilite bearings last?
A: Service life depends on load, speed, temperature, and environment. Under light-to-moderate loads within rated PV limits, Oilite bearings typically last 50,000–150,000 cycles or 5,000–10,000 hours of operation. Continuous high-load or high-temperature operation shortens life by accelerating oil degradation.
Q: Can Oilite bearings be used in high-temperature applications?
A: Standard Oilite bearings with mineral oil are limited to approximately 80–100°C continuous operation. High-temperature variants with synthetic oil can extend this to approximately 150°C. Above this range, the oil degrades rapidly and solid bronze or alternative bearing types should be considered.
Q: What is the difference between Oilite and a solid bronze bushing?
A: Oilite bearings are porous and oil-impregnated, providing self-lubrication from an internal reservoir. Solid bronze bushings are fully dense and rely on external lubrication or solid lubricant inclusions (leaded grades). Oilite is maintenance-free and lower cost at volume; solid bronze handles higher loads and temperatures.
Q: Do Oilite bearings need to be lubricated after installation?
A: No. Properly impregnated Oilite bearings are maintenance-free. The oil is already distributed throughout the porous matrix. In some applications, a light coating of compatible oil on the shaft during assembly helps initial run-in, but ongoing external lubrication is not required.
Q: Can Oilite bearings be custom-sized?
A: Yes. Powder metallurgy tooling can be designed for custom bore, OD, and length dimensions. Standard sizes are most economical because they use existing tooling. For custom bearings, provide dimensional drawings, load and speed requirements, and operating temperature so that material, porosity, and oil type can be matched to the application.
Related Resources
Use these internal links to keep moving through the most relevant guides, service pages, and technical references for this topic.
Oil-Impregnated Bearings
Browse the full product family including iron-based and iron-copper self-lubricating bearings.
Bronze Self-Lubricating Bearings
Review material properties, porosity control, and application guidance for bronze PM bearings.
PM Bearings vs Bronze Bushings
Compare Oilite-type bearings with solid bronze alternatives for load, speed, and temperature.
Request a Quote
Submit bearing dimensions, load conditions, and specifications for quotation support.