Main Bearing Set 0.25 oversize inner Porsche 911 / 964 / 993 / 996 Turbo  ❭  96410190151

Main Bearing Set – 0.25mm Oversize Inner, Standard Outer

Rebuild your Porsche engine with confidence using this OE Match Main Bearing Set featuring 0.25mm oversize inner diameter and standard outer diameter, manufactured to match original factory specifications. Tthis bearing set is intended for engines with a crankshaft that has been reground by 0.25mm on the main bearing journals, while retaining a standard crankcase housing bore.

Fits:

• Porsche 911 1978-1983 3.0L / SC
• Porsche 911 1984-1986 3.2L
• Porsche 911 1987-1989 3.2L G50
• Porsche 911 1975-1977 3.0L Turbo (930)
• Porsche 911 1978-1989 3.3L Turbo (930)
• Porsche 964 (911) C2 1989-93
• Porsche 964 (911) C4 1989-93
• Porsche 964 (911) RS 3.6L 1991-93
• Porsche 964 (911) RS 3.8L 1991-93
• Porsche 964 (911) TURBO 3.3L 1991-93
• Porsche 964 (911) TURBO 3.6L 1991-93
• Porsche 993 (911) C2 1994-97
• Porsche 993 (911) C4 1994-97
• Porsche 993 (911) RS 1994-97
• Porsche 993 (911) C2S 1994-97
• Porsche 993 (911) C4S 1994-97
• Porsche 993 (911) TURBO 1994-96
• Porsche 993 (911) GT2 1994-97
• Porsche 993 (911) TURBO S 1994-97
• Porsche 996 TURBO 2000-05
• Porsche 996 GT3 MKI 1999-02
• Porsche 996 GT3 MKII 2003>>

Precision-manufactured from high-quality bearing materials, these main bearings provide the oil film stability and support required to ensure smooth crankshaft rotation, reduced friction and long engine life. They are the ideal choice for professional engine builders, Porsche specialists and enthusiasts carrying out a complete engine overhaul.

What Do Main Bearings Do?

Main bearings are one of the most critical components inside every Porsche flat-six engine.

Their primary functions include:
Supporting the crankshaft within the crankcase.
Maintaining precise crankshaft alignment during engine operation.
Providing a low-friction bearing surface for smooth rotation.
Maintaining a stable oil film between the crankshaft and bearing shell.
Absorbing combustion and rotational loads throughout the engine.
Helping ensure correct oil pressure and long engine service life.

Correct bearing clearances are essential for maintaining engine reliability and performance.

Why Do Main Bearings Wear?

Over time, engine bearings are subjected to enormous mechanical loads and rely entirely on a consistent supply of clean engine oil.

Common causes of bearing wear include:

• High engine mileage.
• Oil contamination from debris or worn components.
• Insufficient lubrication or low oil pressure.
• Engine overheating.
• Incorrect bearing clearances during previous rebuilds.
• High-performance or competition use.
• Fatigue after repeated heat cycles.

As bearings wear, oil clearance increases, reducing oil pressure and allowing excessive crankshaft movement that can eventually damage the crankshaft and crankcase.

When Should Main Bearings Be Replaced?

Main bearings should always be inspected during engine disassembly and replaced when:

• Carrying out a complete engine rebuild.
• The crankshaft has been reground by 0.25mm on the main journals.
• Bearing surfaces show scoring, wear or fatigue.
• Oil pressure has fallen below specification.
• Bearing material shows signs of overheating or contamination.
• Engine knock or excessive crankshaft clearance has been identified.
• Restoring a high-mileage or performance engine.

Replacing main bearings during an engine rebuild helps ensure correct oil clearances and provides a solid foundation for reliable long-term engine performance.