King Engine Bearings MB5278XPSTDX XP Series Tri-Metal Main Bearing Set Ford 140ci 2.3L L4 STDX

The King Engine Bearings MB5278XP STDX is a high-performance XP Series crankshaft main bearing set engineered for Ford 140ci (2.3-liter) four-cylinder engines. Designed specifically for demanding race and high-performance applications using forged steel aftermarket crankshafts, these bearings are built to withstand extreme loads over extended operating periods. The STDX sizing provides standard crankshaft journal diameter with an additional .001" of oil clearance beyond standard, ideal for builders dialing in precise bearing clearances.

At the core of the XP Series is King's proprietary pMax Black tri-metal structure — an enhanced copper-lead construction with a nickel barrier layer and a hardened performance overlay that is 24% harder than conventional tri-metal race bearings. Combined with King's advanced geometric design features, pMax Black delivers unmatched fatigue resistance and load capacity for circle track, off-road, offshore, and other high-load, long-duration racing disciplines.

Key Features:

• pMax Black Tri-Metal Construction: Enhanced copper-lead intermediate layer with nickel barrier and SecureBond adhesion process ensures superior stability between layers
• 15%–30% Greater Load Capacity than traditional engine bearings, with an intermediate layer rated to 17,000 psi and overlay rated to 10,200 psi
• Bull's Eye Tolerance: Wall thickness matched to ±0.0001" — the tightest tolerances in the industry — for consistent, precise bearing-to-bore fit
• Hardened Performance Overlay: 0.0005" metallurgically enhanced overlay resists surface fatigue and withstands greater sustained loads
• 1/2 Groove Design: Main bearings feature half-groove upper shells to preserve lower shell load capacity while maintaining adequate oil distribution
• Improved Oiling: Enlarged, chamfered oil holes and medium eccentricity promote optimum oil film distribution and load spreading
• Narrowed Shell Design: Reduced bearing width accommodates large-radius crankshaft fillet geometry
• STDX Sizing: Standard crankshaft journal dimension with an extra .001" of running clearance for performance oil clearance builds

King Engine Bearings are manufactured to the highest quality standards, with every shell individually matched to ensure consistency from bearing to bearing — reducing assembly time and eliminating the need to purchase multiple sets to achieve target oil clearance. The MB5278XP STDX is the choice of serious performance engine builders seeking proven durability in the most demanding race applications.