King MB7039XPSTDX XP-Series Main Bearings for 1984-2006 BMW 325/328/323i M20/M50

Vehicle Fitment

• 1984-1987 BMW 325e (E30, Base, M20B27, 2.7L I6, RWD)
• 1986-1988 BMW 325 (E30, Base, M20B25, 2.5L I6, RWD)
• 1986-1987 BMW 325es (E30, Base, M20B27, 2.7L I6, RWD)
• 1987-1995 BMW 325i (E30/E36, Base, M20B25/M50B25, 2.5L I6, RWD)
• 1987-1995 BMW 325is (E30/E36, Base, M20B25/M50B25, 2.5L I6, RWD)
• 1996-2000 BMW 328i (E36, Base, M52B28, 2.8L I6, RWD)
• 1998-2000 BMW 323i (E36, Base, M52B25, 2.5L I6, RWD)
• 1998-1999 BMW 323is (E36, Base, M52B25, 2.5L I6, RWD)
• 2000 BMW 323Ci (E46, Base, M52B25, 2.5L I6, RWD)
• 2001-2006 BMW 325i (E46, Base, M54B25, 2.5L I6, RWD)
• 2001-2006 BMW 325Ci (E46, Base, M54B25, 2.5L I6, RWD)

Fitment Notes

• For use with standard crankshaft journal dimensions only - STDX designation provides +0.001" (0.025mm) additional oil clearance over standard for performance and racing applications
• Engineered for use with forged steel aftermarket crankshafts and performance engine builds with high sustained loads
• Compatible with BMW M20, M50, M52, and M54 inline-6 engine codes only
• Not for use with stock OE crankshafts on street-driven vehicles requiring factory oil clearances - order MB7039XPSTD for standard clearance or MB7039AM for OE replacement
• Does not fit BMW M30, M40, M42, M54B30, S50, S52, or S54 engine families
• Thrust washers are not included - order separately as required

Features

• XP-Series pMax Black tri-metal construction features a copper-lead intermediate layer, nickel plate barrier, and lead/tin/copper Babbitt overlay bonded to a steel backing for maximum fatigue resistance and load capacity
• pMax Black nano-scale hardening process creates a fatigue-resistant black shield that makes the overlay 24% harder (14.5 HV vs. 11.5 HV) than any other conventional tri-metal race bearing
• Industry-leading load capacity of 17,000 psi at the intermediate layer and 10,200 psi at the overlay - engineered for extended high-load, high-RPM racing environments
• STDX sizing delivers +0.001" (0.025mm) additional oil clearance over standard to support increased oil flow and improved cooling under race conditions
• Narrowed bearing width accommodates large-radius crankshaft fillets common on performance and aftermarket forged crankshafts without shell-to-fillet contact
• Enlarged, chamfered oil feed holes improve oil distribution to journal surfaces, reducing the risk of oil starvation during sustained high-RPM operation
• Full 3/4-groove or 1/2-groove oiling configuration ensures consistent oil film across the entire bearing journal surface under race conditions
• Precision wall thickness tolerance held to ±0.0001" - tighter than any competing race bearing - ensuring consistent oil clearance and eliminating the need for multi-set trial fitting
• ONE SET FITMENT design: King XP bearings are the only race bearings engineered so a single set achieves the desired oil clearance without purchasing multiple sets for selective fitting
• Manufactured by King Engine Bearings, a supplier to top-tier circle track, offshore, and road racing programs since 1960, with ISO/TS16949 and AS9100 quality certifications

Specifications

• Part Number: MB7039XPSTDX
• Series: XP-Series (pMax Black Tri-metal - copper/lead intermediate, nickel barrier, Babbitt overlay)
• Size: STDX - standard crankshaft journals with +0.001" (0.025mm) extra oil clearance
• Intermediate Layer Load Capacity: 17,000 psi
• Overlay Load Capacity: 10,200 psi
• Overlay Hardness: 14.5 HV (24% harder than conventional tri-metal)
• Wall Thickness Tolerance: ±0.0001"
• Oil Hole Configuration: Enlarged, chamfered; full 3/4-groove or 1/2-groove oiling
• Bearing Width: Narrowed for large-radius crankshaft fillets
• Position: Crankshaft main journals
• Quantity: Set of 5 bearing shells
• Compatible Engine Codes: BMW M20B25, M20B27, M50B20, M50B25, M52B25, M52B28, M54B25
• Application Type: Performance / Racing - circle track, road racing, drag racing, high-load street builds
• Backing Material: Steel

Included Components

• 5x Crankshaft main bearing shells (XP-Series pMax Black, STDX clearance)

Product Description

The King Engine Bearings MB7039XPSTDX is a performance main bearing set from King's XP-Series line, engineered specifically for BMW M20, M50, M52, and M54 inline-six engine builds running forged steel aftermarket crankshafts under high sustained loads. The STDX designation specifies a standard crankshaft journal diameter combined with +0.001" (0.025mm) of additional oil clearance over factory specification, a setup favored in performance and racing applications to improve oil flow, reduce bearing operating temperatures, and provide a more forgiving clearance window during high-RPM operation. This set covers E30, E36, and E46 BMW 3-Series platforms, spanning the 325e, 325, 325i, 325is, 325Ci, 328i, 323i, 323is, and 323Ci across model years 1984 through 2006.

At the core of the XP-Series is King's pMax Black tri-metal construction - a layered design consisting of a steel backing, copper-lead intermediate layer, nickel plate barrier, and a lead/tin/copper Babbitt overlay that has been hardened through a proprietary nano-scale surface treatment. This process makes the pMax Black overlay 24% harder than conventional tri-metal race bearings, dramatically improving fatigue strength under compressive loads that would crush or extrude softer bearing materials. The intermediate layer sustains up to 17,000 psi of load capacity, while the overlay handles up to 10,200 psi - making these bearings capable of surviving the extended peak loads generated by turbocharged, supercharged, or high-compression naturally aspirated BMW inline-six builds. Wall thickness is controlled to ±0.0001", a tighter tolerance than any competing race bearing, and the bearings are designed with a ONE SET FITMENT philosophy so builders achieve target clearances without purchasing multiple sets for selective fitting.

The XP-Series also features geometrical enhancements specifically suited to performance crankshafts: the bearing width is narrowed to accommodate the larger fillet radii common on forged aftermarket crankshafts, and the oil holes are enlarged and chamfered to maximize oil delivery to the journal surface under race conditions. Full 3/4-groove or 1/2-groove oiling configurations ensure continuous oil film across the bearing contact area even at the oil pressures and RPMs typical of track use. These bearings are not intended as a direct OE replacement for street-driven vehicles requiring factory oil clearances - for standard-clearance applications, King's MB7039XPSTD or MB7039AM variants are the appropriate choice. Thrust washers are not included in this set and must be ordered separately if needed for the application.