ACL 5M1957H-.25 Race Series Main Bearings for Honda/Acura D16 D17 B18 B20 H22 F2

Vehicle Fitment

• 1986-1989 Acura Integra (Base/LS/RS/SE, 1.6L I4 DOHC - D16A1)
• 1998-1999 Acura CL (Base, 2.3L I4 SOHC - F23A1)
• 1999 Acura Oasis (LS, 2.3L I4 SOHC - F23A)
• 1988-1991 Honda CRX Si (1.6L I4 SOHC/DOHC - D16A6, D16A8)
• 1988-2005 Honda Civic (DX/LX/EX/HX/Si/VX, 1.5L-1.7L I4 SOHC/DOHC - D16A6, D16A7, D16A9, D16Y1, D16Y4, D16Y5, D16Y7, D16Y8, D16Z2, D16Z5, D16Z6, D17A1, D17A2, D17A6, D17A7, D17Z1)
• 1993-1997 Honda Civic del Sol (S/Si/VTEC, 1.5L-1.6L I4 SOHC/DOHC - D16Z6, D16Y8, ZC)
• 1998-2002 Honda Accord (DX/LX/EX/SE, 2.3L I4 SOHC - F23A1, F23A4, F23A5, F23A7, F23Z2, F23Z4)
• 1988-2001 Honda Prelude (S/Si/VTEC/SH, 2.0L-2.2L I4 SOHC/DOHC - B20A1-B20A9, B21A, B21A1, H22A4, H22A5, H22A7, H22A8, H22Z1)
• 1998 Honda Odyssey (EX/LX, 2.3L I4 SOHC - F23A)
• Engines: B18A (USA), B18A, B20A, B20A1-B20A9, B21A, B21A1, D16A1, D16A3, D16A6-D16A9, D16B2, D16B6, D16W1, D16Y1, D16Y4, D16Y5, D16Y7, D16Y8, D16Z2, D16Z5, D16Z6, D17A1, D17A2, D17A6, D17A7, D17Z1, F23A1, F23A4, F23A5, F23A7, F23Z2, F23Z4, H22A4, H22A5, H22A7, H22A8, H22Z1, ZC

Fitment Notes

• This is a 0.25mm oversized undersize bearing set - for use on crankshafts that have been reground to a 0.25mm undersize. Do not use on standard-size crankshafts.
• Verify crankshaft journal diameter prior to installation to confirm 0.25mm undersize requirement.
• Does not fit B16A, B17A, B18B, B18C series engines (those use ACL 5M1959H).
• Does not fit K-series (K20, K24) engines.
• ZC engine fitment applies to DOHC ZC variants used in JDM markets.
• Drivetrain: FWD for all applicable vehicles listed above.

Features

• Tri-metal (trimetal) construction combining a steel backing, copper-lead intermediate layer, and high-performance overlay for superior strength and seizure resistance.
• Manufactured to micron-level tolerances using precision measurement systems to ensure consistent wall thickness and bearing crush across all five bearing positions.
• Full-groove design with a single oil hole per bearing half, promoting unrestricted oil circulation around the crankshaft journal at all RPM levels.
• Increased bearing crush for improved retention, maximizing radial contact pressure against the housing bore to eliminate micro-movement under high load.
• No flash plating applied - removes the standard overlay limitation to improve heat transfer and maximize bearing-to-housing contact for demanding performance builds.
• Enlarged inner diameter chamfers accommodate crankshafts with larger fillet radii, common in performance-ground or stroked crank applications.
• High-strength steel alloy backing provides greater tensile strength than OEM bearings, improving load capacity under sustained high-RPM or forced-induction use.
• Identical halves design - both upper and lower bearing shells are interchangeable, simplifying installation and reducing the risk of incorrect orientation during assembly.
• 0.25mm oversized for use with reground crankshafts, restoring proper oil clearance after journal machining without sacrificing performance bearing characteristics.

Specifications

• Part Number: 5M1957H-.25
• Oversize: 0.25mm (undersized for reground crankshafts)
• Bearing Material: F780 Tri-Metal
• Bearing Half Type: Identical halves
• Position: Main crankshaft (all 5 positions)
• Min. Shaft Size (STD ref): 54.980mm / 2.1646 in
• Max. Shaft Size (STD ref): 55.000mm / 2.1654 in
• Min. Tunnel Size: 59.000mm / 2.3228 in
• Max. Tunnel Size: 59.020mm / 2.3236 in
• Max. Wall at Crown: 2.007mm / 0.0790 in
• Max. Overall Length: 20.00mm / 0.7874 in
• Min. Vertical Oil Clearance: 0.031mm / 0.0012 in
• Max. Vertical Oil Clearance: 0.076mm / 0.0030 in
• Design: Full-groove, single oil hole
• Quantity: Set of 5

Included Components

• 5x ACL Race Series Main Bearing Shells (0.25mm Oversized)

Product Description

The ACL Race Series 5M1957H-.25 is a 0.25mm oversized main bearing set engineered for Honda and Acura engines equipped with reground crankshafts. When a crankshaft's main journals become worn or scored, machine shops regrind the journals to an undersized diameter - typically in 0.25mm increments - to restore a smooth surface. This set restores the proper oil clearance on a 0.25mm-reground crank, allowing the engine to be assembled to race-quality specifications without sacrificing performance bearing advantages. Fitment covers a broad range of Honda and Acura inline-4 engines including the D16, D17, B18A, B20A, B21A, H22A, F23A, and ZC engine families found in the Civic, CRX, Civic del Sol, Accord, Prelude, Integra, Odyssey, CL, and Oasis across model years 1986-2005.

ACL Race Series bearings are constructed using a tri-metal F780 alloy consisting of a high-strength steel backing, a copper-lead intermediate layer, and a performance overlay - a composition that delivers substantially higher load capacity and seizure resistance compared to standard OEM bi-metal bearings. The full-groove design with a single oil hole ensures consistent crankshaft lubrication at every RPM, while the increased bearing crush and precision machining lock the shells firmly into the housing to eliminate micro-motion during high-output engine operation. The absence of flash plating further enhances heat dissipation and maintains direct contact between the bearing surface and housing bore, a benefit particularly appreciated in boosted or high-revving builds.

This set includes five identical bearing shells - compatible with both upper and lower positions across all five main journal locations - reducing complexity during engine assembly. The ACL 5M1957H-.25 is the correct choice for builders doing complete bottom-end refreshes on Honda/Acura D-, B-, H-, and F-series engines where crank grinding has been performed. Always mic the crank journals and confirm 0.25mm undersize before ordering; for standard-bore crankshafts, refer to the 5M1957H-STD, and for extra oil clearance applications, consider the 5M1957HX variant.