King Engine Bearings MB639SM0.5 Main Bearing Set Undersize - 0.50mm

The King Engine Bearings MB639SM0.5 is a precision-engineered main bearing set ground to a 0.50mm undersize specification, designed for use during engine rebuilds where the crankshaft main journals have been machined or reground. This undersize fitment restores proper oil clearance and ensures accurate crankshaft-to-block alignment after material removal from worn or damaged journal surfaces.

King Engine Bearings manufactures this set using their proprietary tri-metal bearing construction, which combines a steel backing for structural rigidity, an intermediate copper-lead or aluminum alloy layer for load distribution, and a precision-applied overlay for conformability and embedability. This multi-layer design delivers superior fatigue strength, excellent corrosion resistance, and long service life under demanding operating conditions.

Key Features:

• 0.50mm (0.020") undersize main bearing set for reground crankshafts
• Tri-metal construction with steel backing for superior durability
• High-precision tolerances for optimal oil film thickness and clearance
• Excellent conformability to accommodate minor surface irregularities
• Corrosion-resistant overlay for extended service life
• Meets or exceeds OEM specifications
• Suitable for performance, street, and competition engine rebuilds

King Engine Bearings is a globally recognized supplier trusted by professional engine builders and OEM manufacturers. The SM designation in the part number indicates the standard rod journal width with performance-oriented features, making this bearing an ideal choice for high-quality engine reconditioning applications.