Description
Technical Overview & High-Tensile Metallurgy
In high-output four-stroke marine diesel engines like the Zichai L250 series (including the 6L250, 8L250, and LC9250 platforms), the connecting rod mechanism transforms linear piston energy into rotating crankshaft torque. During the non-firing strokes, massive reciprocating mass inertia pulls the piston and rod upwards, subjecting the L250-06A-006 screws to intense, cyclic tensile stress.
To completely prevent material fatigue, thread stripping, or sudden structural shearing under these severe dynamic loads, our connecting rod screws are treated as critical high-fatigue elastic expansion bolts. They are manufactured under demanding quality parameters:
- Compatible Engine Type: Zichai L250, LB6250, LB8250, 6L250, 8L250, and LC9250 series four-stroke medium-speed marine diesel engines.
- Part Number / Designation: L250-06A-006 (Connecting Rod Screw / Con-Rod Bolt).
- Component Group: Power-Transmission Gear / Connecting Rod Assembly Spare.
- Material Base: High-performance Chrome-Molybdenum or Chrome-Nickel-Molybdenum alloy steel (e.g., 42CrMo or equivalent high-grade structural alloy), vacuum-degassed, quenched, and tempered.
- Thread Execution: Precision-rolled threads (not cut) to preserve continuous steel grain structure and maximize fatigue resistance.
Key Features & Performance Benefits
- Precision-Rolled Thread Matrix: The fastening threads undergo automated cold-rolling after thermal hardening. This process creates compressive residual stresses at the thread roots, significantly improving resistance to fatigue crack initiation compared to standard machined threads.
- Calibrated Elastic Expansion Shifter: Designed with a micro-reduced shank diameter (elastic neck zone). This configuration allows the screw to function like a high-strength mechanical spring, maintaining continuous, pre-stressed clamping force even under severe engine vibrations and thermal transitions.
- Micro-Finished Seating Face: The landing shoulder beneath the screw head is precision-ground completely perpendicular to the shank axis. This layout guarantees uniform torque transmission and eliminates dangerous bending stresses during tightening.
- Advanced Anti-Galling Surface Finish: The body receives a specialized phosphated or copperized coating layer. This coating limits friction variations during installation, preventing thread galling and ensuring predictable torque-to-stretch calibration.
Why Source from Heybeli Marine?
A failed or loose connecting rod screw is one of the most destructive events that can happen inside a crankcase, immediately throwing the con-rod loose to punch through the engine block casting. Heybeli Marine secures your commercial fleet operations and technical safety with:
- Exacting OEM Production Controls: Our Zichai-compatible con-rod screws are sourced from specialized marine forging plants utilizing state-of-the-art non-destructive testing (NDT), ensuring 100% material and dimensional compliance.
- Global Supply Chain Logistics: We maintain dedicated stock levels of Zichai L250 running gear hardware across key international maritime corridors, ensuring fast, 24-hour dispatch to primary dry docks and major trading ports worldwide.
- Comprehensive Overhaul Integration: We supply the L250-06A-006 screw along with matching big-end connecting rod bearings, small-end bushings, gudgeon pins (L250-05-005), and combination pistons (250-110).
- Verified Certification Profiles: Every production lot undergoes rigorous magnetic particle inspection (MPI) to guarantee the total absence of surface micro-cracks or forging inclusions.
Technical Maintenance Note: When executing an engine overhaul or lower-end bearing inspection, meticulous evaluation of the L250-06A-006 connecting rod screws is mandatory. Before reuse, clean the screws thoroughly and measure their total length using a precision micrometer or stretching template against the factory manual’s maximum allowable permanent elongation limit. Any screw showing permanent elongation or thread pitch deformation must be discarded immediately. Never apply an uncalibrated impact wrench for final tightening. Tightening must be executed in multi-stage torque steps combined with exact angle-of-rotation methods (or via direct hydraulic stretching measurements if specified by the builder) using original lubrication specifications on the threads and head landing face to prevent localized over-stressing.