Engine Bearings — Renewal, Crosshead to Thrust Block

1. Two Lubrication Regimes

Fast steady rotation drags oil into a converging wedge that lifts metal off metal — hydrodynamic film, the design condition. Slow, reversing or oscillating motion never builds the wedge, so surfaces rub through a boundary film instead. Every bearing below is a strategy for living in one regime or surviving the other: crossheads oscillate (boundary at dead centres), mains rotate (hydrodynamic throughout), thrust pads tilt to manufacture their own wedge angle.

2. Top End — Guides and Crosshead

Guide shoes on the crosshead ends dump rod side-thrust into the frame on white-metal strips, shim-aligned fore-and-aft with a locating pin stopping crosshead-pin rotation. The crosshead (top-end) bearing is the hard one: oscillation means boundary film at each swing end, hydrodynamic only mid-swing — so cooling oil is injected between pin and lower shell exactly when load is lowest, ~20° before top centre, through shell grooves (sometimes edge-throttled to hold pressure). Big polished pins, continuous lower shells for area, tin-aluminium on steel with white-metal overlay, clearances non-adjustable: at maximum, renew.

Sulzer's RTA variant runs a continuous lower shell in the rod top fed by 10–16 bar booster oil through a swinging arm that also carries 4 bar piston-cooling oil — same problem, higher-pressure answer.

3. Bottom End and Mains — Crush Is the Design

MAN bottom ends feed down rod drillings into white-metal or tin-aluminium thin shells (tin-flashed halves), screwed against rotation, torqued exactly to the book so caps never twist on the rod. On trunk engines the top half carries most of the cycle with a brief mid-cycle transfer below; crankshaft drillings deliver the oil, shell holes and housing grooves distribute it.

Main bearings (2–2.5% wall thickness, steel-backed, full-length rigid support against fretting) add two anti-starvation details: tangential run-outs ease oil into the loaded zone instead of scraping it away, and bore reliefs absorb minor misalignment so no shell edge stands proud as a scraper. Shoulders and screws or pins stop axial walk and rotation; cover-fed oil spreads through a radial groove and shell bores. Trunk-engine mains mirror this with grooved top halves, lugged lower halves, and block-drilled supply.

4. Gudgeon Pin — Frozen Bush, Floating Pin

Trunk small-ends repeat the crosshead problem: bottom-loaded, film-fragile. The answer is area (generous lower bush with spreader grooves) plus fit discipline — bush frozen into the rod, pin floating clearance-fit in the skirt on circlips for self-alignment, fed from the bottom end up the rod (or from piston-cooling oil), with a top-skirt scraper ring stripping carry-over before it reaches combustion.

5. Thrust Block — Propeller Push Becomes Hull Push

Sited aft of the engine (driving end on direct-reversibles), the Michell block anchors propeller thrust into strengthened structure through holding-down bolts. Seven or eight white-metal pads per side of the integral collar each pivot like a sliding block, tilting into the exact wedge angle the film needs; spray nozzles between pads feed both faces from the LO pumps, and a dedicated sump with cooling coils holds temperature.

6. Main-Bearing Renewal — the 22-Step Discipline

Renewal is a permits-first ritual: company permission and immobilisation certificate (main engine unavailable for the stated period), manual studied in a toolbox meeting, tools and spares staged, risk assessment with everyone involved. Only then does steel move:

1. Steps 1–5 — paper before steel. Company permission; immobilisation certificate from the port; manual read plus toolbox meeting on the procedure; tools and spares staged; risk assessment signed by everyone on the job.
2. Steps 6–13 — make the engine unstartable and breathable. Starting-air valve shut; indicator cocks open on all units; turning gear engaged in remote under the in-charge's hand; main LO pump stopped; crankcase doors open, blowers on, space ventilated; enclosed-space checklist prepared; entry only after ventilation, in full PPE.
3. Steps 14–16 — measure first. Depth-gauge tool calibrated and zeroed; LO-pipe screws opened and the gauge inserted to read keep-to-journal clearance; reading compared against history and the new shell's figure — the number decides the renewal, not the eye.
4. Steps 17–22 — lift and land. LO line disconnected; crank throw barred toward the exhaust side for access; hydraulic jacks mounted and stud nuts eased; lifting tool on the keep, hoisted by pulley and wire; keep marking noted for correct refit direction; keep guided out with a second chain block and landed on a wooden base — never on steel.

Warning — two habits that save shells. Keep lifting and marking: lift with control, mark before the keep leaves its saddle — a reversed keep wipes on first firing. And measure before disconnecting anything: once the LO line is off and the jacks are on, the as-found clearance is gone forever.