A linear bearing raceway goes through millions of rolling cycles over its service life, and grease is the only thing standing between clean rolling contact and metal-on-metal wear. SKF's failure analysis data attributes 60–80% of premature bearing failures to lubrication problems — not the wrong bearing, the wrong grease, or none at all.
This guide covers grease selection for round-shaft bushings (LM-series style), pillow block linear bearings, and self-lubricating plain liners. If you're running a profiled rail linear guide — a carriage-and-rail system like THK or HIWIN — the grease specs, fill quantities, and intervals differ; see our Linear Guide Lubrication Guide instead.
| This guide says | Official product category |
|---|---|
| Ball-type bushing | Linear Ball Bearings |
| Self-lubricating plain liner | Linear Sleeve Bearings |
| Pillow block | Mounted Linear Ball Bearings |
Grease Selection by Load and Speed
Most grease problems on round-shaft and pillow block linear bearings come down to a mismatch between the lubricant and the operating conditions, not skipping lubrication entirely. Always cross-check against your bushing manufacturer's datasheet, since seal type and preload class shift the recommendation.
Operating Condition | Recommended Lubricant | Why |
|---|---|---|
Standard duty (most LM-series bushings, pillow blocks) | Lithium-based NLGI Grade 2 grease | Default across most bushing catalogs; balances film strength and pumpability through the Zerk fitting |
Heavy or shock load (pillow blocks under vibration) | NLGI 2 grease with EP (extreme-pressure) additives | EP additives keep the film from breaking down under peak contact stress |
Below 10°C | Low-temperature grease rated to -40°C | Standard NLGI 2 stiffens sharply below 10°C, raising drag on the shaft |
How to Grease a Round-Shaft Bushing or Pillow Block
The mechanics are simpler than greasing a profiled rail carriage, since there's no rail groove to coat — just the bushing bore and the shaft surface passing through it.
Wipe the shaft clean. Remove old grease, dust, and any metal particles before injecting fresh grease — never grease over contamination.
Locate the Zerk fitting. Most round-shaft bushings and pillow blocks have one grease nipple on the housing body; long pillow block runs have one per unit.
Inject slowly with a hand grease gun. There's no need to target a fixed cm³ figure — manufacturers like THK specify replenishing "as necessary according to service conditions" rather than a bore-size chart. Stop as soon as fresh grease appears at the seal edges.
Cycle the shaft by hand. Slide the bushing through its full travel a few times so the grease distributes around the full bore, not just the injection point.
Wipe off the purge. Grease that squeezes out at the seals should be removed immediately — left in place, it collects dust and debris.
Self-Lubricating Plain Liners: When You Don't Need Grease at All
Ball-type bushings aren't the only option. A self-lubricating plain bearing replaces the rolling balls with a solid-lubricant-impregnated liner — PTFE-based composites are the most common — that requires no external grease at all. (These are listed as Linear Sleeve Bearings in our catalog.)
During a break-in period of roughly 50–100 strokes, the liner transfers a microscopic film onto the shaft. After that, the bearing runs dry for its service life.
The tradeoff is a lower load capacity than an equivalent ball-type bushing of the same bore size, and the shaft still needs to stay free of abrasive contamination — the liner protects against friction, not grit.
Internal-Reservoir Pillow Blocks: A Middle Ground
Some pillow block linear bearings include a built-in lubricant reservoir that meters small amounts of grease onto the shaft continuously, rather than relying on periodic manual regreasing. The bearing still consumes lubricant, but the interval between top-offs stretches out well past manual greasing's ~100 km baseline — exactly how far depends on the reservoir technology.
Oil-impregnated felt or "oil-cotton" reservoir kits, one common design, are rated up to roughly 4,000 km on some models; porous-polymer lubrication units from other manufacturers report a wider range — some starting from a more conservative ~1,000 km baseline, others (such as NSK's K1 unit) rated for up to 10,000 km, or roughly five years, under favorable conditions.
Always confirm the exact figure against your specific model's datasheet, since reservoir capacity, grease grade, and design all affect it.
Re-Lubrication Intervals by Bearing Type
Bearing Type | Typical Interval | Maintenance Action |
|---|---|---|
Round-shaft bushing, manual grease | ~100 km (normal) / 30–50 km (harsh environments) | Re-grease via Zerk fitting on schedule |
Pillow block, internal reservoir | ~1,000–10,000 km, depending on reservoir design | Top off reservoir when depleted |
Self-lubricating plain liner | None after ~50–100 break-in strokes | Keep the shaft free of abrasive debris |
Calculate the interval from actual travel distance, not the calendar — a machine doing short, fast strokes can rack up 8–9 km a day and blow past a "monthly" schedule in under two weeks. Our Linear Bearing Noise & Failure Diagnosis guide walks through the exact calculation, plus how to tell whether a noisy bushing needs re-lubrication or replacement.
Signs It's Time to Re-Grease
Between scheduled intervals, a few symptoms mean a bushing is running low on grease before its next travel-based check:
A squeal or increased running noise, especially on startup or in cold conditions
Noticeably higher force needed to slide the shaft by hand
Purged grease coming out dark, gritty, or dry instead of clean gray or amber
Any of these can also point to contamination or raceway damage rather than simple grease depletion — the noise diagnosis guide above breaks down each sound and symptom so you can tell re-lubrication from replacement.
Mistakes Specific to Bushings and Pillow Blocks
Greasing only one end of a long shaft run. On a long shaft supported by two or more pillow blocks, each unit has its own Zerk fitting and needs its own injection — greasing the nearest one doesn't feed the others.
Mixing incompatible greases. Different thickener types — lithium, polyurea, calcium sulfonate — aren't guaranteed compatible. Flush old grease out before switching types rather than topping one on top of another.
Adding grease to a self-lubricating bushing. It won't damage the liner, but it defeats the point — the film-transfer process only works cleanly on a bare shaft, and added grease just attracts dust to a bearing that was designed to run dry.
Over-greasing. Past the point where fresh grease purges at the seals, extra grease just raises running torque and attracts dust in exposed environments.
Frequently Asked Questions
What grease should be used for a round-shaft linear bearing?
Lithium-based NLGI Grade 2 grease covers most standard-duty bushings. Switch to a low-temperature grease below 10°C, or an EP-additive grease under heavy or shock loading.
Do pillow block linear bearings need different grease than shaft bushings?
No — the same load/speed selection logic applies. The difference is mechanical, not chemical: pillow blocks often support longer shaft spans across multiple mounting points, so each unit needs its own regreasing rather than assuming one injection feeds the whole shaft.
Can a self-lubricating linear bearing run without any grease?
Yes, by design. After the initial break-in period of roughly 50–100 strokes, a plain liner bearing transfers its own lubricating film onto the shaft and needs no added grease for the rest of its service life.
Can you use WD-40 on a linear bearing bushing?
No. WD-40 is a light penetrating oil, not a bearing lubricant — it lacks the film strength to protect a loaded raceway and evaporates quickly, leaving the bushing under-lubricated soon after application.
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