Crank position: The crank is turned so that the crankpin is at bottom dead centre (BDC) or at a position where the big-end is accessible and the connecting rod is vertical/ near vertical, giving maximum access to the big-end bolts and the bearing. The engine is barred to this position and the turning gear is then disengaged and locked/ secured.

Safety precautions:

• Stop the engine and secure the turning gear (barring gear) in the disengaged position; tag the engine "not to be turned/ started".
• Isolate the starting air and fuel; drain the lubricating oil from the sump/ crankcase as required.
• Ensure the crankcase is ventilated and the atmosphere is safe before entry (crankcase entry permit).
• Use correct lifting gear and support the connecting rod/ piston so it cannot fall.
• Keep the working area clean, dry and well lit; use the correct tools.
• Protect the crankpin and bearing surfaces from damage and contamination.
• Follow the enclosed-space/ hot-work and permit-to-work procedures as applicable.

• The bearing clearance (diametral) is measured using a feeler gauge at the parting faces (between the bearing shell and the crankpin at the top), or by the lead-wire/ plastigage method: a soft lead wire or plastigage strip is placed across the crankpin, the cap is torqued down, then removed and the flattened wire/ strip measured to give the clearance.
• Compare the measured clearance with the maker's specified range (typically 0.025-0.10 mm per 25 mm of journal diameter for white-metal big-ends).
• Adjustment: If the clearance is too small, remove shims (thin packing) from between the cap and the rod; if too large, add shims. On modern engines without shims, the bearing is renewed or the cap is machined/ the shell replaced to restore the clearance. Always re-torque the bolts to specification and re-check the clearance after adjustment.

• Wiping/ scuffing of the white metal: oil starvation, excessive clearance, overloading, or misalignment.
• Cracking/ sinking of the white metal: fatigue from cyclic loading, poor shell seating, or excessive clearance.
• Scoring/ galling: contamination (dirt, abrasive), oil starvation, or misalignment.
• Pitting: water/ acid in the oil, or cavitation.
• Loose shell (shell not seating/ hammering): incorrect clearance, fretting of the shell back, or damaged locating lugs.
• Excessive clearance: normal wear.
• Seizure: severe oil failure; consequential damage to the crankpin.

• Confirm the bearing clearance is to specification and record it.
• Torque the big-end bolts to specification and check bolt stretch/ locking.
• Confirm the oil ways are clear and the oil supply to the bearing is correct.
• Bar the engine over several revolutions to confirm free rotation and no binding.
• Prime the lubrication system and confirm oil pressure/ flow to the bearing.
• Run the engine at low load initially, monitoring bearing temperature, oil pressure and vibration; then load up and confirm stable temperatures.
• Check the oil filter for debris after running-in.