King Engine Bearings MB5650SI040 SI-Series Main Bearing Set .040 Undersize Ford 370 429 460

The King Engine Bearings MB5650SI040 is a SI-Series bi-metal main bearing set designed for Ford 370, 429, and 460 Big Block 16V OHV engines with a .040" undersize crankshaft. This complete engine set is engineered for aftermarket gasoline engine rebuilding and performance engines running OE or nodular cast iron crankshafts.

About King SI-Series Bearings:

SI-Series bearings feature a unique bi-metal construction built on high-strength steel, using an aluminum alloy reinforced with 2.5–3% silicon. This advanced formulation delivers reliable durability in medium-load applications and serves as a lead-free, environmentally responsible OE replacement bearing. The SI-Series also features an improved crankshaft finish surface to reduce microscopic ferrite peaks commonly found on improperly ground or polished nodular cast iron crankshafts, and delivers improved oil clearance to reduce wear, engine noise, vibration, and excess oil flow.

Key Features:

• SI-Series bi-metal silicon-aluminum construction on high-strength steel backing
• Lead-free bearing material — environmentally sustainable and safe
• Aluminum alloy strengthened with 2.5–3% silicon for medium-load durability
• Improved oil clearance reduces wear and extends engine life
• Reduces operating noise, vibration, and excess oil consumption
• Engineered for OE crankshafts and nodular cast iron crankshafts
• .040" undersize — for use with crankshafts that have been turned down .040"
• Sold as a complete engine set (5 pairs)

Undersize Note: The .040" undersize designation refers to a thicker bearing used when the crankshaft has been turned down (ground) by .040", resulting in an undersized crankshaft journal. Always verify your crankshaft's actual journal diameter before ordering.

Cross-Reference Part Numbers: 5M1039A-STD, MS-1039P