Zichai 250-02-093 Main Bearing Bush (Lower)

Description

Technical Overview & High-Load Architecture

In medium-speed four-stroke marine diesel engines like the Zichai L250 series (including the 6L250, 8L250, and LC9250 platforms), the lower main bearing shell bears the brunt of the power stroke. Every time a cylinder fires, peak combustion pressures exceeding 150 bar push the piston, connecting rod, and crankshaft directly down onto this lower shell.

To prevent the metal from crushing, fatiguing, or wiping under these heavy loads, our lower main bearing bushes utilize a rugged tri-metal composite layout:

• The Steel Backing Layer: Formulated from high-strength carbon steel to provide rigid structural support, high deformation resistance, and a secure press-fit (crush height) inside the main bearing cap.
• The Intermediate Copper-Lead Matrix: A durable cast bronze layer that offers exceptional fatigue strength and high thermal conductivity to quickly pull frictional heat away from the rotating journal.
• The Babbitt Running Overlay: A micro-electroplated soft overlay that provides excellent conformability to adapt to minor crankshaft misalignments and outstanding embeddability to trap tiny abrasive carbon particles.

Key Features & Performance Benefits

• Maximum Load-Bearing Area: By omitting internal oil grooves, the lower shell maximizes its effective contact area. This reduces localized oil film pressures and prevents the lubricating wedge from collapsing under peak combustion shocks.
• High Fatigue and Seizure Resistance: The specialized copper-lead intermediate layer prevents surface spalling and lining cracking under continuous high-torque operations, extending the service life of the engine’s lower running gear.
• Excellent Embeddability Properties: If microscopic hard particles or cat-fines pass through the filtration system, the soft overlay allows them to sink safely into the bearing lining. This keeps the debris from scratching, scoring, or damaging the expensive crankshaft journal surface.
• Precise Anti-Rotation Alignment: Machined with a factory-calibrated locating lug (tang) that locks perfectly into the main bearing cap recess, preventing any accidental rotational movement or structural displacement during high-speed operation.

Why Source from Heybeli Marine?

Worn lower main bearings cause immediate crankshaft misalignment, excessive engine vibrations, a drop in operating oil pressure, and accelerated wear on adjacent connecting rod bearings. Heybeli Marine secures your technical fleet management and vessel operations with:

1. Exacting OEM Material Quality: Our Zichai-compatible main bearing shells are sourced from world-class maritime bearing foundries, ensuring absolute compliance with international marine classification standards.
2. Global Strategic Fleet Inventory: We maintain deep stock allocations of Zichai L250 engine block components across key international maritime hubs for immediate, 24-hour dispatch to your shipyard, port, or dry dock.
3. Comprehensive Matching Packages: We supply the lower main bearing shell alongside matching upper grooved shells, thrust washers, connecting rod bearings, and complete crankcase overhaul kits.
4. Calibrated Undersized Selections: To support reconditioned or ground crankshafts, we offer a full selection of precision undersized bearing shells to safely restore factory oil film clearances.

Technical Maintenance Note: During a main bearing overhaul, meticulous cleanliness is mandatory. Both the back of the 250-02-093 lower shell and the inner bore of the main bearing cap must be completely clean, dry, and free of oil before installation to ensure the shell develops the correct clamping “crush” when torqued. Apply clean lubricating oil only to the front running surface of the bearing overlay and the crankshaft journal. Never attempt to use a lower shell in the upper engine saddle position; the lack of an oil supply groove will cause immediate oil starvation and catastrophic crankshaft seizure within minutes of starting the engine. Always measure journal ovality and calculate oil clearances using an approved plastic gauge method before final assembly.