BC4620 – ACL Subaru EJ25 w/Thrust in #3 position Bearing Set – OEM Sizing

For the builder seeking to extract maximum durability and power from the Subaru EJ25 platform, the selection of engine bearings is a critical decision that transcends simple replacement—it is an investment in foundational engine integrity. The ACL BC4620 Race Series Main Bearing Set with Thrust in #3 Position represents the pinnacle of this component category. Engineered by ACL, a brand synonymous with championship-winning motorsport success, this bearing set is not merely an OEM substitute; it is a purpose-built upgrade designed for high-output, high-stress applications. Utilizing a sophisticated tri-metal construction and precision-aluminum-tin-silicone overlays, the BC4620 set provides the optimal balance of embeddability, conformability, and fatigue resistance necessary to withstand the extreme loads generated by turbocharging, high-RPM operation, and aggressive tuning. This bearing set is the definitive choice for builders who prioritize engineering excellence and long-term reliability in their EJ25 performance builds, from street-driven monsters to full-race engines.

Engineering Superiority: The ACL Race Series Advantage

The ACL BC4620 set distinguishes itself from standard replacement bearings through its advanced tri-metal (AlSnSi/CuPb/Sb) race material. This architecture is the result of decades of ACL’s direct involvement in premier motorsport categories, where bearing failure is not an option. The key to its performance lies in the layered approach: a strong steel backing provides dimensional stability, a high-load copper-lead intermediate layer offers excellent fatigue strength, and the precision-aluminum-tin-silicone running surface delivers superior embeddability and anti-seizure properties. This combination is crucial for the EJ25, particularly in modified turbo applications where detonation and particulate contamination are ever-present risks. The bearing’s ability to safely embed minute contaminants prevents abrasive wear on the crankshaft journals, while its exceptional fatigue resistance ensures it can handle the increased cylinder pressures and harmonics of a built engine without flaking or spalling.

Optimal Clearance & The Critical Thrust Washer Design

ACL manufactures the BC4620 bearings to precise OEM sizing specifications, ensuring a correct fit for standard-crank applications without requiring custom machining. However, the true performance benefit is delivered through ACL’s engineered clearance ranges. These are optimized for performance use, typically offering a slightly larger operational clearance than a standard OEM bearing. This controlled increase promotes superior oil flow across the bearing surface, enhancing cooling and reducing the risk of oil film breakdown under extreme thermal loads—a common failure point in stressed EJ25 engines. The inclusion of the thrust washer in the #3 position is a masterstroke for drivetrain longevity. This design centralizes axial crankshaft loads, managing the forces generated by the clutch and gearbox more effectively than other configurations, thereby reducing the potential for crankshaft walk and associated catastrophic failure.

Tangible Performance Benefits for Your EJ25 Build

Installing the ACL BC4620 bearing set translates into measurable gains in engine robustness and performance potential. The benefits are systematic and significant.

• Enhanced Durability Under Load: The tri-metal construction provides superior fatigue strength, directly combating the bearing failures common in high-horsepower and high-torque EJ25 builds.
• Improved Contaminant Management: The soft aluminum-tin-silicone overlay safely embeds microscopic debris, protecting your expensive crankshaft from abrasive scoring and extending the life of both components.
• Optimized Thermal & Lubrication Management: Engineered clearances ensure consistent oil film stability, improving heat dissipation from the crankshaft and maintaining critical lubrication under high-RPM and high-temperature conditions.
• Maximum Load Capacity: The material and design support the significantly higher cylinder pressures found in forced-induction applications, making them essential for any turbocharged EJ25 build aiming for reliable power.
• Precision OEM Fitment: Manufactured to exacting standards, these bearings drop into a properly prepared block with OEM-spec crankshaft dimensions, eliminating guesswork and ensuring correct initial assembly.

Vehicle Fitment & Application Specifics

The ACL BC4620 bearing set is engineered specifically for the Subaru EJ25 engine platform. It is crucial to verify your engine’s specifications prior to purchase. This set is designed for standard size (STD) crankshaft journals and requires that the engine block’s main bearing housings be within factory specification. It is a direct replacement for OEM bearing sets in a wide range of vehicles, including but not limited to:

Primary Applications: Subaru Impreza WRX (2002-2005, 2006-2007 for specific EJ255 variants), Subaru Impreza STI (2004-2007 USDM), Subaru Forester XT (2004-2008), Subaru Legacy GT (2005-2009), and Subaru Outback XT (2005-2009) equipped with the EJ255 or EJ257 engine. Critical Note: Always cross-reference your engine’s serial number and main journal diameters. This set is intended for performance rebuilds and assumes the builder has the expertise to measure and verify all clearances, as detailed in authoritative technical resources like this guide on understanding engine bearing clearances.

Technical Specifications & Installation Context

Installation of the ACL BC4620 set is a procedure that demands mechanical precision. It is not a task for the novice. Plastigage or precision micrometers must be used to verify the actual running clearance in your specific engine assembly, as block machining, crankshaft grinding, and tolerances all affect the final number. The bearings must be installed in a surgically clean environment with copious lubrication. The thrust washer alignment in the #3 cap is critical and must be set according to factory service manual procedures, including proper crankshaft rotation to align the washers during final torque sequencing. This bearing set is the cornerstone of a build that respects the forces at play within a performance EJ25, ensuring your investment in forged internals and forced induction is protected by the highest-quality foundational componentry available.