ACL 5M1959H-.25 Race Main Bearing Set +0.25mm Honda B16A B18C K20A2 K24A RSX

Vehicle Fitment

• 1989-2001 Honda Civic / CRX / Del Sol - B16A variants (1.6L DOHC VTEC)
• 1992-1993 Acura Integra GS-R (B17A1, 1.7L DOHC VTEC)
• 1990-2001 Acura Integra GS/LS/RS (B18A1/B18B1/B18B2, 1.8L DOHC)
• 1994-2001 Acura Integra GS-R / Type-R (B18C1/B18C5, 1.8L DOHC VTEC)
• 1997-2001 Honda CR-V (B20B / B20Z, 2.0L DOHC)
• 2002-2005 Honda Civic Si EP3 (K20A3, 2.0L DOHC i-VTEC)
• 2002-2006 Acura RSX / RSX Type-S (K20A3 / K20A2, 2.0L DOHC i-VTEC)
• 2003-2007 Honda Accord (K24A, 2.4L DOHC i-VTEC)
• 2002-2014 Honda CR-V (K24A, 2.4L DOHC i-VTEC)
• 2003-2011 Honda Element (K24A, 2.4L DOHC i-VTEC)
• 2004-2008 Acura TSX (K24A2, 2.4L DOHC i-VTEC)
• 2007-2012 Acura RDX (K23A1, 2.3L DOHC Turbo)

Fitment Notes

• The .25 suffix designates this as the +0.25mm oversize bearing set - for use when the crankshaft main journals have been ground 0.25mm undersize. This is the more significant regrind step, typically required when main journals have suffered deeper wear or surface damage beyond what the .025mm step can address. For standard journal diameter, use 5M1959H-STD. For crankshafts ground 0.025mm undersize, use 5M1959H-.025.
• This single set covers both the Honda/Acura B-series (B16A through B20Z) and K-series (K20A2/A3/Z1, K24A/A2/Z1) inline-4 engines - all share the same crankshaft main journal dimensions despite differences in displacement and application.
• Always measure crankshaft main journal diameter with a micrometer before selecting bearing size. Confirm actual clearance with Plastigage or a dial bore gauge after assembly.
• Sold as a complete set of 10 bearing shells (5 pairs, upper and lower) - sufficient for all 5 main journal positions in one 4-cylinder engine.

Features

• Tri-metal construction: copper-lead alloy lining bonded over a hardened steel backing, with a high-strength overlay plate - engineered for the high-RPM and forced-induction demands of performance-built Honda B-series and K-series engines.
• Hardened steel backing on all main bearings improves structural support of the bearing lining and maintains crush under elevated crank loads in high-power B-series and K-series builds.
• High-strength overlay plate with reduced thickness provides improved fatigue resistance compared to OEM-spec bearings - critical in boosted or sustained high-RPM applications across both engine families.
• Increased bearing crush and tighter wall tolerances ensure consistent, secure seating in the block main journal bores, reducing the risk of bearing movement.
• Enlarged ID chamfers on bearing edges accommodate the larger fillet radii found on performance and aftermarket Honda crankshafts.
• 3/4-groove upper main bearings optimize oil supply to the main journals and to the connecting rod bearings through the crankshaft oiling passages.
• Elimination of flash plating on bearing backs improves heat transfer and maximizes grip between the bearing shell and the block main bore.
• Increased eccentricity compensates for bore distortion at high RPM and assists in the formation of a stable hydrodynamic oil film under load.

Specifications

• Part Number: 5M1959H-.25
• Product Line: ACL Race Series
• Application: Crankshaft Main Bearings
• Engine Compatibility: Honda/Acura B16A variants (1595cc); B17A1 (1678cc); B18A1, B18B1, B18B2 (1834cc); B18C1, B18C2, B18C5, B18C7 (1797cc VTEC); B20B, B20Z (1972cc); K20A2, K20A3, K20Z1 (1998cc); K24A, K24A2, K24Z1 (2354cc)
• Crankshaft Size: +0.25mm Oversize (for main journals ground 0.25mm undersize)
• Shaft (Main Journal) Diameter: 54.730-54.750mm (2.1547-2.1555 in)
• Tunnel (Housing Bore): 59.000-59.020mm (2.3228-2.3236 in)
• Maximum Wall Thickness at Crown: approx. 2.127mm (0.0837 in)
• Maximum Overall Length: 20.0mm (0.787 in)
• Bearing Material: Tri-Metal Copper-Lead Alloy / Hardened Steel Backing
• Quantity: Set of 10 Shells - 5 Upper + 5 Lower (complete engine set)

Included Components

• 10x Race Series Crankshaft Main Bearing Shells - +0.25mm Oversize (5 upper, 5 lower)

Product Description

The ACL Race Series 5M1959H-.25 crankshaft main bearing set is the +0.25mm oversize option for Honda/Acura's broad B-series and K-series inline-4 engine family - covering the full range from the B16A-powered Civic and CRX to the B18C Type-R Integra, B20B CR-V, and the complete K20/K24 lineup found in the RSX, Civic Si, Accord, Element, and TSX. All share identical crankshaft main journal dimensions, making this a single set for any of these engines at the +0.25mm oversize step.

This oversize set is selected when main journals have been ground 0.25mm undersize - a more significant regrind typically required when journals have sustained deeper wear, scoring, or surface damage that cannot be corrected at the finer .025mm step. Built on ACL's Race Series tri-metal platform, these main bearings deliver superior fatigue resistance and oil film stability over OEM Honda shells. Always confirm clearances at assembly. Sold as a complete set of 10 shells for one engine.