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- Porsche 911 1974-1977 2.7L / 1976-77 3.0 Carrera
- Porsche 911 1975-1977 3.0L Turbo (930)
Main Bearing Set 0.25mm Oversize Inner - Standard Outer
Main bearings support the crankshaft within the crankcase
and provide the accurately controlled running clearance required for reliable
lubrication and smooth crankshaft rotation. This set is intended for engines
requiring a 0.25mm oversize inner bearing specification and is supplied with 12
bearings plus 2 thrust bearings.
Fits:
- Porsche 911 1974-1977 2.7L / 1976-77 3.0 Carrera
- Porsche 911 1975-1977 3.0L Turbo (930)
Diagram Ref No 23 and 24
Specification: 0.25mm oversize inner / standard outer
Contents: 12 bearings + 2 thrust bearings
What Do the Main Bearings Do?
Main bearings support the crankshaft as it rotates within the engine. Pressurised oil creates a lubricating film between the crankshaft journals and bearings, reducing friction and wear.
The thrust bearings also control axial movement of the crankshaft.
Why Do Main Bearings Wear?
Bearing wear can result from:
- High engine mileage
- Low oil pressure or oil starvation
- Contaminated engine oil
- Incorrect bearing clearances
- Crankshaft journal wear
- Engine overheating
- Previous internal engine damage
The cause of abnormal bearing wear should always be identified during an engine rebuild.
Why Use 0.25mm Oversize Bearings?
This is not a standard-size bearing set.
The 0.25mm oversize inner specification is intended for an engine where the crankshaft has been measured or machined to require this corresponding bearing size.
Accurate crankshaft and crankcase measurements are essential before ordering. Oversize bearings should not be selected simply because the existing bearings are worn.
When Should Main Bearings Be Replaced?
Main bearings should be inspected during an engine rebuild and replaced if they show scoring, excessive wear, surface damage, incorrect clearance or evidence of oil starvation.
Crankshaft journals, bearing housings, oil passages and thrust surfaces should also be inspected before assembly.
Main Bearing Sets
Correct main bearing selection is essential when rebuilding an air-cooled Porsche flat-six engine. The bearings support the crankshaft, maintain the required oil clearance and help ensure reliable lubrication throughout the engine.
This OE Match 0.25mm oversize inner main bearing set is designed for Porsche 911 2.7 and 930 Turbo 3.0 engines requiring this specific bearing dimension.
Always measure the crankshaft journals and crankcase accurately before selecting standard or oversize bearings. Design911 supplies Porsche main bearings, thrust bearings and associated engine rebuild components for classic air-cooled Porsche applications.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
91110190250
The product you are viewing cross references to these numbers
- Porsche Boxster 987 2.7L 2005-08/08
- Porsche Boxster 987 S 3.2/3.4L 2005-08/08
- Porsche 996 C2 3.6L 09/01-2005
- Porsche 996 C4 3.6L 09/01-2005
- Porsche 996 C4S 3.6L 09/01-2005
- Porsche 997 MK1 Carrera 2 3.6L 2005-08
- Porsche 997 MK1 Carrera 2S 3.8L 2005-08
- Porsche 997 MK1 Carrera 4 3.6L 2005-08
- Porsche 997 MK1 Carrera 4S 3.8L 2005-08
- Porsche Cayman 2.7L 987C 2006-08
- Porsche Cayman S 3.4L 987C 2005-08
A complete set of crankshaft main bearings - these are the half-shells (upper and lower) that support the crankshaft main journals inside the engine block. The set replaces all main-bearing shells to renew the engine bottom end’s bearing surfaces.
SET OF 14 Bearing Shells
Fits:
Engine code: M96.03
Porsche 996 3.6L
Engine code: M97.21 / M97.22
Porsche 987 Cayman
Porsche 987 Boxster
Porsche 997 3.6L / 3.8L
Diagram Ref No 13.
Sold as a full set of 14 bearing shells - enough to rebuild the entire main bearing bank of a six-cylinder boxer engine.
When installed, this bearing set:
• Provides a precise, low-friction journal surface for the crankshaft to rotate on
• Maintains correct bearing clearance and oil film under high loads and RPMs, ensuring smooth rotation and reducing wear.
• Helps preserve oil pressure and lubrication flow, preventing oil starvation and bearing damage.
• Restores engine reliability and reduces risk of bearing knock, wear or failure, especially on re-built or high-mileage engines.
Over time and use, main bearings wear down - surfaces can score, bearings can become pitted, clearance can increase, oil film may degrade, leading to:
• Engine knocks or bearing rumble
• Loss of oil pressure
• Excess crankshaft play or vibration
• Accelerated wear of crank pins, journals and engine internals
Replacing main bearings with a fresh set restores factory-correct clearances and bearing surfaces, ensuring smooth crankshaft rotation, proper oil flow, and long engine life - especially important after high mileage, rebuilding, or performance modification.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610120904
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche Boxster 987 2.7L 2005-08/08
- Porsche Boxster 987 S 3.2/3.4L 2005-08/08
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
- Porsche 996 C2 3.6L 09/01-2005
- Porsche 996 C4 3.6L 09/01-2005
- Porsche 996 C4S 3.6L 09/01-2005
- Porsche 997 MK1 Carrera 2 3.6L 2005-08
- Porsche 997 MK1 Carrera 2S 3.8L 2005-08
- Porsche 997 MK1 Carrera 4 3.6L 2005-08
- Porsche 997 MK1 Carrera 4S 3.8L 2005-08
- Porsche Cayman 2.7L 987C 2006-08
- Porsche Cayman S 3.4L 987C 2005-08
OE Match set of 12 big end bearing shells in standard size engineered to replace the original connecting rod bearings used on Porsche Boxster 986 / 987 and 911 996 / 997 and 987 Cayman platforms
Set of 12 Bearing Shells
Fits:
Porsche 986 Boxster 1997 - 2004
Porsche 987.1 Boxster 2005 - 2008
Porsche 987C.1 Cayman 2006 - 2008
Porsche 996 1997 - 2005
Porsche 997 2005 - 2008
Diagram ref no 12.
Each bearing shell is produced with smooth, low-friction bearing surfaces and consistent wall thickness to maintain correct rod-to-crankshaft clearances when installed in the rod big end. The standard size designation indicates these bearings retain factory bore dimensions, ideal for engines where no crankshaft undersize machining has been performed.
Big end bearing shells provide the low-friction interface between the connecting rod and crankshaft journal. They help to support dynamic engine loads and maintain a stable lubricating oil film that protects both the rod and crankshaft from metal-to‐metal contact. With proper oil flow and clearance, these bearings help ensure reliable rotation and reduce wear under normal and high-load conditions.
Installed in pairs inside each connecting rod’s big end bore, these bearing shells support the rotating crankshaft by maintaining correct clearance and offering a durable, smooth surface for the journal to ride on. Their design promotes even oil distribution and stable hydrodynamic lubrication - essential for wear resistance, smooth engine operation, and long service life.
Big end bearings are central to engine bottom-end integrity. They endure high loads, RPMs, and constant motion. Over time or due to lubrication issues, bearings can wear, lose material, or show surface degradation - leading to increased clearances, knocking noises, reduced oil pressure, and accelerated wear of the crankshaft journal. Replacing worn bearings with OE Match shells during a rebuild restores proper oil clearances and hydrodynamic lubrication, helping protect the crankshaft and rod journals from premature wear while supporting smooth, reliable engine operation.
When to replace:
• Engine is undergoing rebuild or overhaul
• Bearing wear, noise, or rod knock detected
• After lubrication or oil starvation incident
• During high-mile preventive maintenance
• When crankshaft journals are within standard size (no undersize needed)
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610312162
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche Boxster 987 2.7L 2005-08/08
- Porsche Boxster 987 S 3.2/3.4L 2005-08/08
- Porsche 996 C2 3.4L 1997-08/01
- Porsche 996 C4 3.4L 1997-08/01
- Porsche 996 C2 3.6L 09/01-2005
- Porsche 996 C4 3.6L 09/01-2005
- Porsche 996 C4S 3.6L 09/01-2005
- Porsche 997 MK1 Carrera 2 3.6L 2005-08
- Porsche 997 MK1 Carrera 2S 3.8L 2005-08
- Porsche 997 MK1 Carrera 4 3.6L 2005-08
- Porsche 997 MK1 Carrera 4S 3.8L 2005-08
- Porsche Cayman 2.7L 987C 2006-08
- Porsche Cayman S 3.4L 987C 2005-08
12 x Big end bearing shells in standard size
12 x Connection Rod Bolts
6 x Connection Rod Bearing
Engineered to replace the original connecting rod bearings used on Porsche Boxster 986 / 987 and 911 996 / 997 and 987 Cayman platforms
Fits:
Porsche 986 Boxster 1997 - 2004
Porsche 987.1 Boxster 2005 - 2008
Porsche 987C.1 Cayman 2006 - 2008
Porsche 996 1997 - 2005
Porsche 997 2005 - 2008
Diagram ref no 10, 11 & 12.
Each bearing shell is produced with smooth, low-friction bearing surfaces and consistent wall thickness to maintain correct rod-to-crankshaft clearances when installed in the rod big end. The standard size designation indicates these bearings retain factory bore dimensions, ideal for engines where no crankshaft undersize machining has been performed.
Big end bearing shells provide the low-friction interface between the connecting rod and crankshaft journal. They help to support dynamic engine loads and maintain a stable lubricating oil film that protects both the rod and crankshaft from metal-to‐metal contact. With proper oil flow and clearance, these bearings help ensure reliable rotation and reduce wear under normal and high-load conditions.
Installed in pairs inside each connecting rod’s big end bore, these bearing shells support the rotating crankshaft by maintaining correct clearance and offering a durable, smooth surface for the journal to ride on. Their design promotes even oil distribution and stable hydrodynamic lubrication - essential for wear resistance, smooth engine operation, and long service life.
Big end bearings are central to engine bottom-end integrity. They endure high loads, RPMs, and constant motion. Over time or due to lubrication issues, bearings can wear, lose material, or show surface degradation - leading to increased clearances, knocking noises, reduced oil pressure, and accelerated wear of the crankshaft journal.
Replacing worn bearings with OE Match shells during a rebuild restores proper oil clearances and hydrodynamic lubrication, helping protect the crankshaft and rod journals from premature wear while supporting smooth, reliable engine operation.
When to replace:
• Engine is undergoing rebuild or overhaul
• Bearing wear, noise, or rod knock detected
• After lubrication or oil starvation incident
• During high-mile preventive maintenance
• When crankshaft journals are within standard size (no undersize needed)
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99610312162
The product you are viewing cross references to these numbers
This kit is comprised of the following items:
