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Porsche > 964 (911) (1989-1994) > 964 (911) TURBO 3.6L 1991-93 > Engine Rebuild Parts >

Crankcase Parts

Crankcase Parts

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Rear main oil seal. Porsche 964 / 993 / 996 - 99911342641, 21074, 99911321440, 99911321540, 99911324240, 99911326440, 99911327040, 99911342640, 99911342641, 99911346140, 569.120
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Rear main oil seal. Porsche 964 / 993 / 996
99911342641/1
Product Information
Product Information

Rear Main Oil Seal for Porsche 

Restore engine sealing integrity and prevent costly oil leaks with this OE Match Rear Main Oil Seal for the Porsche 964, Porsche 993 and Porsche 996. Manufactured to OE specifications and measuring 90mm inner diameter, 110mm outer diameter and 12mm width, this critical engine seal is designed to prevent engine oil escaping around the rear of the crankshaft where it exits the engine case and connects to the flywheel assembly.

Fits:

  • 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 GT2 2001-05
  • Porsche 996 GT3 MKI 1999-02
  • Porsche 924S 2.5L 1986-87
  • Porsche 924S 2.5L 1988
  • Porsche 944 2.5L 8V 1982-87
  • Porsche 944 2.7L 8V 1988-89
  • Porsche 944S 2.5L 16V 1987-88
  • Porsche 944S2 3.0L 16V 1989-91
  • Porsche 944 Turbo 2.5L 8V 1985-88
  • Porsche 944 Turbo 2.5L 8V 1989-91
  • Porsche 944 Turbo S 2.5L 8V 1988
  • Porsche 968 3.0L 1992-94
  • Porsche 968 Sport 3.0L 1994-95
  • Porsche 968 CS 3.0L 1993-95
  • Porsche 968 Turbo S 3.0L 1993-94
  • Porsche 928 4.5L 1978-82
  • Porsche 928S 4.7L 1981-83
  • Porsche 928S2 4.7L 1984-86
  • Porsche 928S4 5.0L 1987-92
  • Porsche 928GT 5.0L 1989-91
  • Porsche 928GTS 5.4L 1992-95

Diagram Ref No. 21

The rear main oil seal, often referred to as the RMS (Rear Main Seal), is one of the most important sealing components in the engine. It retains engine oil inside the crankcase while allowing the crankshaft to rotate at high speed. A worn or damaged seal can lead to oil leaks, clutch contamination and unnecessary engine maintenance costs if left unattended.

This OE Match replacement provides the correct fit, sealing performance and durability required for maintenance, engine rebuilds and preventative servicing.

What Does the Rear Main Oil Seal Do?

The rear main oil seal forms a seal around the rear section of the crankshaft.

Its primary functions include:

  • Preventing engine oil leaks
  • Sealing the rear crankshaft opening
  • Protecting the flywheel area from contamination
  • Maintaining correct engine oil levels
  • Preventing oil reaching the clutch assembly
  • Supporting long-term engine reliability
  • Allowing smooth crankshaft rotation

Without a properly functioning rear main seal, oil can escape from the engine and create a range of reliability issues.

Why Do Rear Main Oil Seals Fail?

Like all rubber sealing components, rear main oil seals are subject to wear and ageing.

Common causes of failure include:

  • Heat cycling
  • Age-related hardening
  • Crankshaft wear
  • Engine vibration
  • Long-term oil exposure
  • Improper installation
  • Excessive crankcase pressure
  • High mileage use

Over time, the sealing lip can lose flexibility and its ability to maintain consistent contact with the crankshaft surface.

Symptoms of a Failing Rear Main Oil Seal

Common warning signs include:

  • Oil leaks between engine and gearbox
  • Oil drips beneath the vehicle
  • Oil contamination around the flywheel housing
  • Clutch slip caused by oil contamination
  • Burning oil smell
  • Gradual oil level loss
  • Oil residue on transmission bellhousing

Because the seal is located behind the flywheel, leaks can often be mistaken for other engine oil leaks unless properly diagnosed.

When Should the Rear Main Oil Seal Be Replaced?

Replacement is recommended when:

  • Oil leakage is present
  • The gearbox is being removed
  • Replacing the clutch assembly
  • Rebuilding the engine
  • Refurbishing the crankshaft
  • Carrying out preventative maintenance
  • The original seal shows signs of ageing
  • Engine mileage is high

Many Porsche specialists recommend replacing the rear main seal whenever the clutch or flywheel is removed, as labour access is significantly easier during these procedures.

Why Replacement Matters

A leaking rear main oil seal can lead to far more expensive repairs if ignored.

Benefits of replacement include:

  • Prevention of engine oil leaks
  • Protection of the clutch assembly
  • Improved engine cleanliness
  • Reduced maintenance costs
  • Improved reliability
  • Professional rebuild standards
  • Long-term sealing performance
  • Greater peace of mind

Replacing the seal during clutch or engine work is considered a smart preventative maintenance measure.



Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99911342641
99911342641
21074
99911321440
99911321540
99911324240
99911326440
99911327040
99911342640
99911342641
99911346140
569.120

The product you are viewing cross references to these numbers
Temperature switch. Porsche 964 - 93061711800
2
Temperature switch. Porsche 964
Special Order item
93061711800
Product Information
Product Information
Temperature switch.
porsche

Fits:
Porsche 964 Turbo 3.6L 1993-94

Click 'Zoom in' for large parts diagram.
Diagram ref no 46.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

93061711800
93061711800

The product you are viewing cross references to these numbers
DISPLAYING 49 to 50 (of 50 products)
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About Crankcase Parts

Precision Crankcase Parts – Strength, Balance, and Reliability for Porsche Engines

The crankcase forms the core of every Porsche engine, housing key rotating components such as the crankshaft, bearings, and connecting rods. It provides structural rigidity, oil containment, and precise alignment for the engine’s moving parts — making it critical to both performance and longevity.

At Design911, we offer a wide range of precision-engineered crankcase components, including bearing shells, seals, breather valves, dowels, plugs, and fasteners, all manufactured to exacting tolerances. Each part is crafted from high-strength, heat-resistant materials to ensure lasting durability and performance under the most demanding driving conditions.

Whether you’re restoring an air-cooled 911 or maintaining a modern 992, our manufacturer-quality crankcase parts ensure perfect fitment, oil-tight sealing, and reliable performance for years to come.

What Do Crankcase Parts Do?

Crankcase components perform vital structural and lubrication roles within the engine, protecting internal parts and maintaining pressure balance.

Core Functions:

  • House and support the crankshaft, connecting rods, and bearings.
  • Contain and distribute oil to lubricate moving components.
  • Maintain structural rigidity to prevent vibration and misalignment.
  • Control crankcase ventilation to reduce oil contamination and pressure build-up.

In performance and classic Porsche engines alike, the crankcase ensures stability, smooth rotation, and reliable oil management — key to consistent power and reduced wear.

Why Do Crankcase Parts Fail?

Over time, crankcase components can degrade due to heat cycles, vibration, oil contamination, and mechanical fatigue. When neglected, these failures can lead to oil leaks, pressure imbalance, and even catastrophic engine damage.

Common Causes of Failure Include:

  • Oil seal wear causing leaks and pressure loss.
  • Bearing fatigue from prolonged high load or low oil pressure.
  • Warped surfaces due to overheating or corrosion.
  • Clogged breather valves causing pressure build-up and oil blow-by.
  • Fastener fatigue leading to structural loosening or vibration.

Replacing worn crankcase parts during an engine rebuild or maintenance interval is essential to preserve oil control, alignment, and crankshaft integrity.

Why Replace with Precision-Engineered Crankcase Parts?

High-quality crankcase components ensure your Porsche engine retains its strength, sealing capability, and precise alignment — essential for performance, reliability, and longevity.

Key Benefits:

  • Restores internal alignment for smooth crankshaft rotation.
  • Prevents oil leaks and pressure loss, maintaining engine performance.
  • Improves lubrication control and bearing life.
  • Reduces vibration and noise caused by worn or loose components.
  • Crafted from corrosion- and heat-resistant materials for lasting strength.
  • Perfect fitment and tolerance for air-cooled and water-cooled Porsche engines.

Engineers and restorers trust precision crankcase parts to maintain Porsche’s legendary reliability and mechanical balance — whether on the road or the track.

Highlights:

  • Comprehensive range of crankcase seals, bearings, bolts, and breather components.
  • Precision-machined parts designed for high-load, high-temperature performance.
  • Manufacturer-quality materials and tolerances.
  • Perfect for classic engine restorations and high-performance rebuilds.
  • Improves oil management, structural rigidity, and reliability.
  • Compatible with air-cooled and modern Porsche engine architectures.

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