Lubricating cast bronze bushings – grease, oil and grooves
A solid cast bronze bush is not self-lubricating. It runs on the grease or oil you give it, and the groove pattern decides where that lubricant goes. This page is the practical part: which lubricant for which duty, the eight groove patterns we machine with codes you can write on a drawing, where the oil hole goes, and how to think about the relubrication interval.
Is bronze self-lubricating? No. Sintered oil-impregnated bronze, graphite-plugged bronze and metal-polymer bushes are self-lubricating because lubricant is stored inside the material; a machined cast bronze bush has no reservoir and depends on external grease or oil. In return it carries three to four times the load of a sintered bush and can be re-machined, re-grooved and re-greased for decades.
- Grease for slow, oscillating, intermittent and dirty positions – most pins, pivots and hinges
- Oil for continuous rotation, higher speeds and where heat must be carried away
- Groove pattern chosen by movement (oscillating / rotating / reciprocating / thrust) and lubrication method
- Oil hole and grooves in the unloaded zone – never where the shaft presses
- Dry running only for seconds; a dry bronze bush on steel scores the shaft and seizes
Grease or oil?
Grease stays where it is put, seals against dirt and needs no circuit, so it is the choice for the large majority of cast bronze positions: excavator pins, tipper hinges, agricultural pivots, press guides, gate hinges. Oil carries heat away and reaches every point of a rotating bore, so it is the choice for continuously rotating spindles, gearbox and pump bushes, and anything above about 0.5 m/s or 100 °C where grease would be worked out or oxidised.
| Duty | Lubricant type | Selection principle | Groove pattern |
|---|---|---|---|
| Slow oscillation, intermittent, outdoors, dirt | Grease, NLGI 2, lithium or lithium-complex, base oil ISO VG 150 – 460 | High base-oil viscosity for the film, EP additives above ~10 N/mm², water-resistant thickener outdoors | G1 short bushes · G2 straight · G4 figure-eight |
| Heavy shock load, low speed | Grease NLGI 1 – 2 with EP and solid additives (MoS₂, graphite) | Solid additives bridge boundary contacts at start-up and under shock | G5 double figure-eight · G8 pockets |
| Continuous rotation, moderate speed | Oil, ISO VG 68 – 220, circulating or oil bath / wick | Viscosity for the speed–load combination; film thickness first, then cooling | G6 spiral · G3 circumferential with pressure feed |
| High temperature 120 – 250 °C | High-temperature grease (polyurea / bentonite, synthetic base oil) or oil with suitable flash point | Above ~150 °C most greases oxidise fast – shorten the interval or consider a graphite-plugged bush | G3 · G4 with generous reservoirs |
| Water, seawater, wet product | Water-resistant grease (calcium sulfonate, aluminium complex) or medium lubrication | Choose a wash-out resistant grease; alloy matters as much – LG2 or aluminium bronze | G2 · G4; consider medium-lubricated plain bore |
| Food, drink, pharma | H1 food-grade grease or oil | Same principles, registered lubricant; lead-free alloy (CuSn12, aluminium bronze) | G1 · G2 |
Types and principles, not brands: any major lubricant maker has a product in each row. Confirm compatibility with seals and with the previous grease before changing.
Oil groove patterns and when to use each
Eight patterns cover practically every plain bush. Write the code on the drawing or in the enquiry ("G4, 2 grooves, 3 × 1.5 mm") and the groove needs no further description; groove width and depth are proportioned to the bore unless you specify them. Grooves are milled or turned after boring and deburred; they never break through to the end faces unless asked, so the grease is kept inside.
- G1
Plain bore – no grooves
Short bushes (L ≤ d), grease-packed on assembly, low speed; also bores finished in place. Grease is held by the running clearance and the chamfers.
- G2
Straight axial grooves
Oscillating pins and long bushes; one to four grooves in the unloaded zone, stopping short of the ends. Spreads grease along the length, easy to machine, the default for excavator and agricultural pins.
- G3
Circumferential groove
One ring groove at mid-length, fed by the oil hole; for rotation with a load direction that changes and for pressure-fed oil, since the ring distributes to the whole circumference. Not for grease-only oscillation (the grease sits in the ring).
- G4
Figure-eight (crossed) grooves
The all-round grease pattern for rotating and oscillating bushes: two crossing diagonal grooves distribute grease both axially and around the bore and wipe fresh grease into the load zone at each stroke.
- G5
Double figure-eight / X-and-ring
Figure-eight plus a ring groove or a second X for heavily loaded, intermittently moving bushes under boundary lubrication – more reservoir volume and more edges to redistribute grease; for large bores above Ø80.
- G6
Spiral (helical) groove
Continuous rotation in one direction, oil lubricated: the helix pumps oil along the bore from the feed end. Also used to carry grease through long rotating bushes. Hand of the helix follows the shaft rotation.
- G7
Radial face grooves (thrust washers, flange faces)
Four to eight radial grooves on a sliding face, from the bore towards the outside without breaking through, so that grease is carried under the rotating counterface. Standard on thrust washers and on the flange face of bushes that take axial load.
- G8
Grease pockets (dimples)
Drilled or milled pockets in the unloaded half of the bore act as separate reservoirs for slow, very heavily loaded bushes – crane pivots, press bushes, mould guides – where a groove would cut the bearing area too much.
Codes G2 – G8 are the order-code suffix (660-404840-G2). Groove size default: width ≈ 0.1 × d (min. 2 mm), depth ≈ half the width; edges rounded. A groove in the load zone halves the bearing area and pumps grease out – keep it in the unloaded half unless the load rotates.
Oil holes and grease fittings
The oil hole enters from the housing side, in the unloaded zone, and meets the groove or the plain bore; its diameter is 1/8 to 1/6 of the bore for grease (3 mm minimum), smaller for oil. The hole is deburred and chamfered on the inside so the edge does not scrape the shaft. The grease fitting (Zerk / hydraulic nipple, or a grease cup) sits in the housing, not in the bush, and the housing hole is aligned with the bush hole before pressing – mark the bush position or use the flange as the reference. A relief hole or an open groove end lets old grease and grit escape on positions that are greased often.
Suffix H in the order code adds one oil hole in the middle of the length; give the angular position relative to the load or to a flange feature if it matters, or say "hole at 90° to the load zone" and we place it.
For your enquiry:Say whether the oil hole is in the bush, the housing or both, and the load direction.
Relubrication interval
The interval depends on load, speed, temperature, contamination and sealing more than on the bush, so no single number is right. The principle: relubricate before the old grease is displaced or dried – the bush must never run on the residue. Start with the machine maker's schedule or the interval used on comparable positions; halve it above 80 °C, in water or dust, and for pins that move in one direction under load; extend it where grease still purges clean at the joint. Purge until fresh grease shows at the seal; wipe the excess so that dirt does not stick.
Dry running: a cast bronze bush with the grease gone heats within minutes, the bronze smears and the shaft is scored; a seized bush then spins in the housing and ruins that too. If a position cannot be relubricated on schedule, a graphite-plugged bush or a metal-polymer bush is the right part, not a larger grease reservoir.
Lubrication by application
What the main markets for cast bronze bushes actually do:
- Excavator and loader pins – EP lithium-complex grease NLGI 2, daily to weekly from the central system or by gun, G2 or G4 grooves, hardened pins
- Agricultural pivots and hinges – lithium NLGI 2 before and after the season and at the intervals in the manual; G1 or G2; grease-packed on assembly
- Pumps and valves – lubricated by the pumped medium or water; LG2 or aluminium bronze, plain bore or G2, larger clearance for particles
- Steel-mill, kiln and furnace equipment – high-temperature grease or solid lubrication; aluminium bronze or C86300, G3 / G4 with reservoirs; where relubrication is impossible, graphite-plugged bronze
- Presses, machine tools, spindles – oil, circulating or bath; tin bronze; G6 spiral or G3 ring; finish bore in place
Frequently asked questions
Do bronze bushings need grease?
Cast bronze bushings – yes, always. They have no lubricant reservoir of their own and run on the grease or oil supplied; only sintered oil-impregnated, graphite-plugged and metal-polymer bushes run without relubrication.
What is the best grease for bronze bushings?
For most positions an NLGI 2 lithium or lithium-complex grease with a high base-oil viscosity (ISO VG 150 – 460) and EP additives; water-resistant thickener outdoors, high-temperature grease above 120 °C, H1 grease in food plants. The type matters more than the brand – see the selection table.
Can I run a bronze bushing dry?
No, beyond a few seconds at start-up. Dry bronze on steel scores the shaft and the bush seizes. For positions that cannot be relubricated, choose a self-lubricating type – graphite-plugged bronze or metal-polymer.
Should the oil groove be in the load zone?
No. Grooves and the oil hole belong in the unloaded half of the bore; in the load zone they cut the bearing area and pump the grease out. Only a load that rotates with the shaft calls for a full ring groove (G3) or figure-eight (G4).
How do I specify grooves on a drawing?
Write the pattern code (G1 – G8), the number of grooves, width × depth if you want to fix them, and the position relative to the load or an oil hole – e.g. "G4, 2 grooves 3 × 1.5, oil hole Ø4 at 90° to load". Without sizes we proportion the groove to the bore.
Is bronze self-lubricating?
Solid cast bronze is not. "Self-lubricating bronze" means a sintered bronze impregnated with oil (SAE 841 / Oilite type) or a cast bronze with graphite plugs – different products with a quarter of the load capacity of a cast bush.
Pick a groove pattern and add it to your quote
Or send the drawing without one and we suggest the pattern, oil hole and grease type for the duty. Samples in 3 – 5 days.