FITTING A SPARE BOTTOM END BEARING (WHITE METAL CRACKED) AND TESTS BEFORE RETURNING TO SERVICE

1. Preparation: With the medium-speed diesel generator stopped and secured, bar/lock the engine, drain the sump, and obtain the maker's manual and a genuine spare bearing (white-metal/ bimetal or tri-metal shell, machined to the correct size). Tag the machine not-to-run.
2. Gain access: Remove the sump/ bedplate door, the big-end bearing cap bolts and lift the connecting rod bottom end. Position the crank so the big-end is accessible (usually at bottom centre). Crank pin should be inspected.
3. Remove the old bearing: Withdraw the two bearing caps/ shells (the big-end is a split "house" formed by the rod's big-end housing bottom cap and the crank-pin cap). Remove the old white metal ('lead/babbit' or leaded-bronze or trimetal layers) carefully - it may be bonded to the shell by swaging. Note the clearance.
4. Inspect the crank pin/ journal and the bearing housing: check for scoring, pitting, out-of-round (micrometer), and that the housing mouths are clean. Correct any damage.
5. Fit the spare bearing: Fit the bearing shells into the two halves of the big-end housing; the bearing must be a clearance fit/ lightly pressed as per maker. Fit new shims/ adjust the cap to set the correct diametral clearance (typically 0.025-0.10 mm per 25 mm of journal diameter, but per maker). Set the bearing so the two shell halves have the correct end float/ niminal end clearance and that the crank pin rotates without binding. Torque the big-end bolts to specification using a torque wrench, in the correct sequence; always fit new bolts/ nuts if the manual requires.
6. Check the big-end bolts stretch/ torque and the locking/ split pins; check the flywheel/ crank end clearance as required.
7. Refit the sump/ crankcase doors, refit oil connections and refill with clean lubricating oil to the correct level.

1. Bar the engine over by turning gear, checking free rotation and that the bearing does not bind or rub at any position (feel for tight spots; there should be a slight shake/ vertical float).
2. Check/ set the big-end bearing vertical clearance within limits (use the correct feeler/gauge).
3. Prime the lubrication system: run the lube oil pump (or bar-over with oil supply) to confirm oil reaches and wets the big-end bearing and that the oil pressure/temperature are normal and no leaks at the new joint.
4. Cold-crank check (without ignition/ or with fuel off) using the starter to confirm oil pressure is established.
5. Vibration/noise: run the generator at low load initially, monitoring bearing temperature (should remain cool and stable), vibration, and oil pressure; then load up gradually to full load and monitor for a steady bearing temperature within limits.
6. Perform a compression/ indicator check if accessible and confirm smooth running, no knocking, and that oil pressure stays within specification at load.
7. After a running-in period, re-check the big-end bolt torque and the oil filter for debris (the bearing bedding-in may shed small particles).