King Engine Bearings MB5803XP STDX Tri-Metal Race Main Bearing Set BMW S65B40A

Featuring King's renowned pMaxBlack™ tri-metal construction, this set delivers race-proven durability and superior load capacity over OEM bearings — making it the preferred choice for engine rebuilds, performance builds, and track-day applications.

The STDX designation provides 0.026mm of additional clearance over the standard STD size, giving builders precise oil clearance control on standard-diameter crankshafts. STDX shells can also be mixed with STD shells to fine-tune exact clearance targets.

pMaxBlack™ XP Series Technology:

• Tri-metal construction — lead bronze intermediate layer with nano-scaled Babbitt overlay for maximum fatigue resistance
• pMaxBlack™ overlay — proprietary nano-scaled hardening process rated to 10,200 PSI fatigue resistance
• 24% greater load capacity and 17% more fatigue resistance versus standard bearings
• SecureBond — micro-etch process that improves multi-layer adhesion and structural integrity
• Copper-based intermediate alloy strengthened with 4.5% tin; industry-leading hardness of 115 HV
• Bull's Eye Tolerance — tightest shell-to-shell wall thickness variation in the industry
• 90° U-Groove oil channel — maintains oil flow integrity and expands load-bearing surface area
• Optimized crush height and eccentricity — engineered via elasto-hydrodynamic analysis for perfect seating
• Compatible with all steel crankshafts; ideal for circle track, drag racing, and high-RPM street/track use

Bearing Specifications (STD reference):

• Housing diameter: 62.705 – 65.034 mm
• Bearing length: 21.70 mm
• Maximum wall thickness: 2.496 mm
• Set includes: 5 pairs (10 shells total)

King Engine Bearings has been manufacturing precision engine bearings since 1960, with an extensive motorsport heritage and a dedicated R&D TechLab recognized as an authority in bearing science. The MB5803XP STDX is a direct performance upgrade over the factory BMW S65B40A main bearings, which are known to wear prematurely under high-load and high-RPM conditions.