Babbitt Bearing Repair: When to Rebabbitt, Re-bore or Replace

A babbitt bearing is a plain bearing with a soft white metal lining on its working surface. Journal bearing is the type of bearing and babbitt is the lining, so the two terms overlap without meaning the same thing: one names the shape that carries the load, the other the material the shaft runs on.

This article starts after the damage has been found. It covers what the alloy means for a repair, how to read what is left, the rebabbitting process from strip to final test, and a rule for choosing between dressing, re-boring, rebabbitting and replacement. How the oil film carries the rotor, and the usual ways a lining fails, are in our guide to steam turbine journal bearings, so they are not repeated here.

Babbitt Bearing vs Journal Bearing: Which Word Means What?

A journal is the part of a shaft that sits in a bearing. A journal bearing supports it from around the circumference, either as a plain sleeve or as a ring of tilting pads. The term describes geometry and says nothing about the surface material.

Babbitt describes the material. ASTM B23 is a specification for white metal bearing alloys, known commercially as babbitt metal, so "white metal" is simply the British name for the same family. Thrust bearings carry the same linings on their pads.

Not every journal bearing is babbitted, because some run on bronze or other liners. In a steam turbine, though, "the bearing needs rebabbitting" has a plain meaning. The soft layer is worn, damaged or debonded, and the steel shell behind it may be perfectly good.

Tin-Based or Lead-Based: The Alloy Is Part of the Repair

ASTM B23-20(2025) covers eight alloys in bar or ingot form. Four are tin-based (alloy numbers 1, 2, 3 and 11) and four are lead-based (7, 8, 13 and 15). A supplier's data sheet for the standard's grades shows how far apart they sit. Reade's table lists Grade 2, a tin-based alloy, at 88 to 90 percent tin, 7 to 8 percent antimony and 3 to 4 percent copper, with no lead listed. Its listed melting point is 241°C and its pouring temperature is 424°C. Grade 7, a lead-based alloy, is 74 to 76 percent lead, 9.3 to 10.7 percent tin and 14 to 16 percent antimony, and its pouring temperature is 338°C.

Two things follow for a repair.

Match the alloy to the drawing. Nobody can tell tin-based metal from lead-based metal by looking at a used bearing. Take the alloy from the bearing drawing or the OEM record. If neither exists, have the old lining analysed before it is melted out. A shop that pours whatever is in the pot is changing the bearing.

Pour at the temperature the alloy needs. The two alloys above are poured 86°C apart. A pour that is too cold risks a poor bond, and one that is too hot risks overheating the shell and its tinned surface. Ask the shop for the pouring and shell temperatures it recorded, because both belong on the job record.

Turbine duty favours tin. Lead-based alloys cost less and suit slower, lighter loads, and I would not accept one on a turbine bearing unless the OEM specified it. Our journal bearings guide notes that turbine bearings almost always use a tin-based grade.

What a Rebabbitt Fixes and What It Does Not

A fresh lining restores the surface. It does not remove the reason the old one failed, and four findings in particular change the repair itself.

Tin oxide. On a tin-based lining, a hard, dark brown or black film is the sign. William Strecker of Kingsbury, writing in Machinery Lubrication in 2004, says it forms from tin babbitt, oil and salt water, starting where temperature and pressure are highest, that it cannot be dissolved, and that it stops the lining embedding dirt. Salt water may not be the only route. R. W. Hiley's 1979 Institute of Marine Engineers paper on ships' turbine and gearbox bearings found that water as low as 500 ppm could make an oil corrosive, and that oils varied greatly. So relining alone will not do. Strecker's remedy for tin oxide on thrust shoes is to replace the shoes and the oil, then flush the bearing assembly, reservoir and piping. Our guide to turbine lube oil analysis covers where water gets in, and on a plant cooled by sea or brackish water I would look at the oil cooler first.

Bond loss behind copper. On a copper-alloy backing, tin from the babbitt can diffuse into the copper, especially when hot, and leave a weak, brittle interface. The authors of the paper "Babbitted bearing health assessment" (Whalen, Hess, Allen and Craighton), excerpted in Turbomachinery magazine, say the bond can look intact, that visual, penetrant and ultrasonic checks often miss the problem, and that measuring bond strength is destructive. They also say none of the affected bearings their company had seen failed in service. Their remedy is a barrier layer applied before babbitting. When a copper-backed pad goes out for rebabbitting, ask whether the shop applies one and ask to see the process record.

Fatigue and lining thickness. Fatigue cracks start at the surface and run towards the bond line, where they turn, spread round the circumference and loosen pieces of lining. The same authors say a thinner lining and a lower metal temperature both improve fatigue resistance. Lining thickness is a design decision that belongs on the OEM drawing, and I would not let a shop change it on its own say-so.

Spark erosion on thrust pads. In the paper's thrust bearing example, electrical erosion began at the minimum film thickness corner of the pad and worked down it. Grounding brushes that work drain the charge safely. A pad rebabbitted without fixing the grounding will be eroded again.

Four findings that change the repair, and what a fresh lining does not cure. Source: Turbomachinery magazine, 'Bearing failure mechanisms' (2019); Strecker, 'Troubleshooting Tilting Pad Thrust Bearings', Machinery Lubrication (2004).

How to Inspect a Babbitt Bearing Before You Decide

Start with the evidence as found. Strecker writes about thrust bearings and says the approach adapts to other fluid film bearings, and his first instruction holds for all of them: do not clean it first, because "valuable information may be lost." Photograph the surface with a scale in frame, note where the damage sits against the load and the direction of rotation, and take bore and clearance readings before anything is wiped down.

Then test the bond, which the eye cannot judge. The ultrasonic and penetrant tests under ISO 4386 are outlined in our journal bearing guide. What matters here is their limit: they tell bonded metal from unbonded metal and do not measure bond strength, which is why the process record matters as much as the test.

Finally, look at the shell. A shell that has overheated, or had old metal melted out of it, can move. Check the split line, the bore and the back fit against the drawing. A shell that cannot be brought back to the drawing is a replacement, however good the lining looks.

The Rebabbitting Process, Step by Step

A good shop can show a record for each step below. A shop that cannot is asking you to take the bond on trust.

Strip. The old lining is melted out of the shell and the metal kept for recycling. The shell is then examined and, where needed, machined back to drawing dimensions to receive the new lining.

Clean. Oil, carbon and old metal are removed. Contamination worked into the steel is what ruins a bond, so a heavily soiled shell may need several rounds of heating, wire brushing and solvent cleaning.

Flux and tin. The cleaned shell is fluxed and coated with a thin layer of tin or tin alloy, which is what the new metal bonds to. The tinned surface is checked for even coverage, and bare patches are tinned again.

Cast. The babbitt is poured at the pouring temperature for its alloy, by static or centrifugal casting, as described below.

Cool. Cooling is controlled, not left to chance. In centrifugal casting, water is sprayed on the outside of the spinning shell so that the lining freezes from the shell inward.

Machine. The bore is finished to drawing diameter, oil grooves and relief are cut, and lining thickness is measured.

Test and record. The bond is tested, and bore, clearance and thickness are recorded. Those figures become the baseline for the next inspection.

Static or Centrifugal Casting?

George Kingsbury's series on bearing materials, archived by Machine Design, describes centrifugal relining this way. The shell is preheated and coated by immersion in molten tin or tin alloy. It is then spun, molten babbitt is admitted, and centrifugal force spreads the metal around the inside wall while water cools the outside. He says the result is a fine-grained, evenly thick lining fully bonded to the backing, and that the method suits large-diameter, thick-wall bearings made in small numbers and one-piece full-round bearings. He also notes that linings thicker than about 0.004 in (0.1 mm) are universally cast.

Static casting pours the metal into a stationary shell held in a fixture and lets it freeze there. It is the usual alternative for shapes that cannot be spun.

I would not rule either method in or out in advance. Ask which the shop uses for your bearing and why, then judge the result by the bond test and the dimensional record.

The rebabbitting process from strip to final record, with the record each step should leave. Source: MIMAH engineering practice; Kingsbury, Machine Design, for centrifugal casting.

Thrust Pads and Tilting Pad Bearings

Pads need their own rules, because each pad has to carry its share. Strecker's checks for a tilting pad thrust bearing start with the contact marks. Indentations from the lower levelling plates show how heavily the base ring was loaded, and a bright contact spot on the upper levelling plate shows where the shoe pivot works. A large, flattened contact spot on a shoe support points to hard contact, and if the shoes do not rock freely in every direction he says to replace them.

Cracked shoes can be reused only if the cracks are removed and the original surface is restored. The collar matters as much as the pads. A rough or scored collar is restored by lapping or hand stoning, or replaced, and new bearings should never go onto a visibly damaged rotor. A collar that is not square to the shaft makes the levelling plates equalise continuously and wear fast.

For any rebabbitted tilting pad, the thickness of every pad is checked against the drawing, along with the pivot, as set out in our journal bearing guide.

Rebabbitt, Re-bore or Replace: A Rule You Can Apply

Four routes are open, and the evidence picks the route.

Dress and return. Choose this when the bond has tested sound, the damage is shallow and confined, clearance is inside the OEM limit, and the cause has been found and removed.

Re-bore. Re-boring takes the lining back to a true, round surface. It removes babbitt and adds none, so the bore only gets bigger, and a bore already worn too large cannot be brought back this way. It works where the lining is sound and well bonded, the finished bore stays inside the clearance limit, and the lining stays above the drawing's minimum thickness. Ovality or shallow local damage with clearance to spare are good candidates. General wear, cracks, debonding and tin oxide are not. Tilting pads are a separate case, because pad thickness sets their clearance.

Rebabbitt. Choose this when the lining is debonded, cracked, deeply wiped or oxidised, or when clearance has opened past the limit or machining would leave the lining too thin, and the shell is dimensionally sound with its fits intact. It is the standard repair, and the bond decides its quality.

Replace. Choose this when the shell is cracked or distorted past what machining can recover, the housing fit is lost, tilting pad pivots are worn out, or tilting shoes carry tin oxide. Replace as well when the design is the cause, as with a fixed geometry bearing that keeps whirling. Where the OEM no longer supplies the part, a replacement is made by measuring the old bearing and manufacturing to the recovered dimensions, which is reverse engineering and is often quicker than waiting on a supply line that has closed.

Cost sits behind all four routes, and it depends on bearing size, alloy, access to a casting facility and what the shop finds when the old metal comes out. Our guide to steam turbine overhaul cost explains how to carry a base scope plus a discovery contingency, which is how a bearing finding should be budgeted.

The evidence picks the route: dress and return, re-bore, rebabbitt or replace. Source: MIMAH engineering practice.

Before You Send a Bearing to a Shop

The common mistake is to reline the bearing and restart without finding out why it failed. The wider list of turbine faults that end in bearing damage is in our article on common steam turbine failures, and the scope of a bearing job inside a larger repair is in the steam turbine repair guide.

Send the evidence with the bearing: photographs as found, the oil analysis history, metal temperature and vibration trends, the drawing and alloy, and the clearance readings taken before removal. Ask for the same in return: the alloy certificate, the tinning and pouring records, the bond test report and the final dimensions.

MIMAH is independent of any one OEM, and our rotating equipment team investigates why bearings fail and reverse engineers critical spares where original supply has lapsed. If you have a wiped shell on the bench, a bearing that keeps running hot or a machine with no drawings, get in touch.