A bearing that wipes weeks after a main engine overhaul is one of the more expensive things that can happen to a chief engineer, because the obvious conclusion - the bearing was faulty - is almost never the real cause. In our workshop in the Al Hayl Industrial Area, Fujairah we strip a steady flow of wiped shells, and the damage pattern nearly always points back to something that happened during or shortly before the overhaul.
This article sets out the six causes we see most often, what each one looks like on the bearing surface, and the measurements that tell them apart. It is written for the superintendent or chief engineer trying to decide what to check before ordering another set of shells.
Read the damage before you order parts
The wiped surface is evidence. Before anything is cleaned or scrapped, photograph the shell in good light, note which half wiped, and note where on the shell the damage sits. Wiping across the whole crown tells a different story from wiping at one edge, and both are different from a shell that is polished bright in a narrow band.
1. Oil supply interrupted, not oil quality
The most common cause is simply that oil did not reach the bearing at the moment load came on. That can be a slow priming after box-up, a partially blocked oil hole in the shell or journal, a bearing fitted with the oil groove misaligned to the drilling, or a pre-lubrication step that was skipped before the first start.
The tell is heavy wiping over a broad area of the crown with the white metal smeared rather than cracked, often on the loaded half only. Check that the oil hole in the shell lines up with the drilling, that the engine was pre-lubricated and turned on turning gear before starting, and that the filter differential was normal on first run.
2. Clearance set at the wrong end of the tolerance
Too little clearance and the oil film cannot form; too much and the film loses pressure and the journal hammers. Both end in a wipe, but the timing differs - tight clearances usually fail within hours of first load, while excessive clearance produces a slower fatigue-type failure with a hammered, cracked appearance.
Clearance must be verified by measurement, not assumed from the part number. We take journal diameter with a micrometer at several points and positions, and confirm the fitted clearance with bridge gauge or lead wire, recording both against the maker's limits.
A bearing ordered as "standard" fitted to a journal that has been ground undersize at some point in the engine's life is a surprisingly common trap - especially on second-hand tonnage where the grinding was never recorded in the engine history.
3. Poor contact area from incomplete scraping
On bearings that are hand scraped, the contact area matters as much as the clearance. If the shell is bearing on a small proportion of its surface, the load per unit area at those points is far higher than designed, and the white metal will fail there first regardless of how good the oil is.
The evidence is a wipe concentrated in one or two patches with clean, undamaged metal between them. In our workshop the shell is blue-checked against the journal and scraped until the contact pattern meets the maker's specification, and the final pattern is photographed before the bearing leaves the bench. If your bearing supplier cannot show you that, you are trusting rather than verifying.
4. Crankshaft alignment and deflection out of limits
If the crankshaft is out of alignment, the journal does not sit square in the bearing and the load concentrates on one edge. The classic signature is wiping heavy at one end of the shell and clean at the other, repeating in a pattern across several units.
Crankshaft deflections should be taken before and after the overhaul and compared with the maker's limits. Where deflections are drifting, the cause is usually further away than the bearing - engine seating, chocks and holding-down bolts, or hull deflection with loading condition. Renewing bearings without correcting alignment simply resets the clock.
5. Dirt built into the assembly
A single hard particle rolled into the bearing during box-up will score the journal and initiate a wipe. The signature is a scored journal with matching embedded debris in the white metal, often with the rest of the shell in good condition.
- Bag and cover every opening while the crankcase is open.
- Wipe oil ways through and confirm they are clear before the shell goes in.
- Renew or clean filters at the first opportunity after the overhaul, and cut the old element open to look at what it caught.
- Take a lube oil sample after the first period of running and have it analysed - white metal in the results is an early warning that costs almost nothing to obtain.
6. Running-in load applied too early
Newly fitted bearings need a controlled load ramp so the surfaces bed in. Going straight to full load because the vessel is under commercial pressure is a decision, not an accident - and the resulting wipe is far more expensive than the delay would have been.
Diagnostic checklist
| What the bearing looks like | Most likely cause | Confirm by |
|---|---|---|
| Broad smearing across the crown, loaded half | Oil starvation at start-up | Oil hole alignment, pre-lubrication procedure, filter differential on first run |
| Failure within hours of first load | Clearance too tight | Journal micrometer readings, bridge gauge or lead wire against maker's limits |
| Hammered, cracked white metal after weeks | Clearance too large or bond failure | Fitted clearance measurement, ultrasonic or tap test on bond |
| Two or three isolated wiped patches | Insufficient scraped contact area | Blue-check contact pattern against the journal |
| Heavy at one edge, repeating across units | Crankshaft alignment or deflection | Deflection readings before and after, seating and chock inspection |
| Scored journal with embedded particles | Dirt built in at box-up | Filter element inspection, lube oil analysis for white metal |
What we do when a bearing comes to our Fujairah workshop
- Photograph and record the damage pattern before cleaning.
- Measure the journal for ovality and taper, and take deflection readings where the shaft is accessible.
- Assess the shell for bond failure and cracking - not every shell is worth re-metalling.
- Re-metal, bore to the measured journal size, then hand scrape and blue-check to the specified contact area.
- Return the bearing with measured clearances and the contact pattern recorded in writing.
The point of the written record is that if the bearing does wipe again, you can eliminate the refit as a cause in minutes instead of arguing about it. Read more about our white metal bearing refitting and crankshaft grinding and polishing work in Fujairah.