Perfect Circle MS804H20 Main Bearing Set Oldsmobile V8 400/425/455 -.020" Undersize H-Series

The Perfect Circle MS804H20 is an H-Series, -.020" undersize crankshaft main bearing set engineered for Oldsmobile V8 engines including the 350 Diesel, 400, 425, and 455 cubic inch applications from 1965 through 1985. This set is the correct choice when a crankshaft has been reground to a -.020" undersize journal dimension.

Perfect Circle, a Federal-Mogul brand with decades of OEM and aftermarket bearing heritage, produces this set using a tri-metal TM-77 bearing material — a high-performance copper-lead alloy construction with a steel backing — designed to deliver excellent load capacity, conformability, and wear resistance in classic American V8 engines.

Key Features:

• Bearing Series: H-Series high-performance
• Size: -.020" (0.020 inch) crankshaft undersize
• Bearing Material: Tri-metal TM-77 copper-lead alloy construction
• Groove Configuration: Positions 2, 3, 4, and 5 are full annular grooved for optimized oil distribution
• Set Includes: 5 main bearings (upper and lower shells)
• Applications: Oldsmobile V8 350 Diesel, 400, 425, and 455 engines (1965–1985)

Designed as a precision replacement during engine rebuilds, the MS804H20 restores proper crankshaft clearances and oil film integrity on worn or reground Oldsmobile big-block and mid-block V8 crankshafts. The full annular groove design at positions 2–5 ensures consistent lubrication around the full bearing circumference under demanding conditions.