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- Porsche 911 1965-1968 2.0L / 912 SWB (F)
- Porsche 911 1968-1973 2.2L / 2.4L / 2.7L RS LWB (F)
- Porsche 911 1974-1977 2.7L / 1976-77 3.0 Carrera
- 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)
Crankcase Through Bolt O-Ring
Sold each - 24 required per engine
The Porsche Crankcase Through Bolt O-Ring is a
small but critically important sealing component used in Porsche 911 engines
from 1965 to 1989. Fitted around the crankcase through bolts that secure the
engine case halves together, this O-ring helps prevent oil leakage from one of
the most common sealing points found on classic air-cooled Porsche engines.
Fits:
- Porsche 911 1965-1968 2.0L / 912 SWB (F)
- Porsche 911 1968-1973 2.2L / 2.4L / 2.7L RS LWB (F)
- Porsche 911 1974-1977 2.7L / 1976-77 3.0 Carrera
- 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)
Diagram ref no 22
Although inexpensive, these O-rings play a vital role in maintaining the integrity of the engine lubrication system. When properly installed, they create a reliable seal around the through bolts, preventing pressurised engine oil from escaping the crankcase and helping to keep the engine clean and leak-free.
Whether you're performing a complete engine rebuild, repairing oil leaks, or restoring a classic Porsche 911, replacing the crankcase through bolt O-rings is considered essential preventative maintenance.
What Does the Crankcase Through Bolt O-Ring Do?
The through bolt O-ring seals the openings where the crankcase through bolts pass through the engine case.
Its primary functions include:
- Preventing oil leaks from the crankcase
- Maintaining crankcase sealing integrity
- Supporting proper oil system operation
- Helping preserve engine cleanliness
- Reducing oil loss and contamination
- Protecting engine components from oil seepage
Because Porsche air-cooled engines operate with a high-capacity dry-sump lubrication system, maintaining effective sealing throughout the crankcase is crucial for long-term reliability.
Why Does the Through Bolt O-Ring Fail?
Over time, the O-ring is exposed to extreme engine heat, oil, pressure fluctuations, and age-related deterioration.
Common causes of failure include:
- Rubber hardening due to heat cycles
- Age-related shrinkage
- Loss of elasticity
- Oil exposure over decades of use
- Improper installation
- Damage during assembly
- Long-term storage and inactivity
As the O-rings age, they gradually lose their sealing ability and become one of the most common sources of oil leaks on classic Porsche 911 engines.
Common Symptoms of a Failing Through Bolt O-Ring
Signs that the O-rings may require replacement include:
- Oil leaks around the crankcase
- Oil residue underneath the engine
- Persistent oil drips despite replacing other seals
- Oil staining around through bolt locations
- Excessive oil mist accumulation on the engine case
- Leaks becoming worse as the engine reaches operating temperature
These leaks are often mistaken for rocker cover, timing chain housing, or crankshaft seal leaks due to the way oil travels across the engine casing.
When Should You Replace It?
Replacement is strongly recommended whenever the engine is disassembled.
The through bolt O-rings should always be replaced:
- During complete engine rebuilds
- During crankcase splitting procedures
- When repairing major oil leaks
- During full engine restorations
- On high-mileage engines undergoing overhaul
- Whenever the crankcase through bolts are removed
- As preventative maintenance during engine refurbishment
Because access requires significant engine disassembly, replacing these O-rings during rebuild work is considered standard Porsche engine-building practice.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99970100640
The product you are viewing cross references to these numbers
This Item is an Original Porsche Part found by using our original Porsche Part Number Search. If you are ordering parts via this method it is your responsibility to make sure that you enter and purchase the correct products for your vehicle. Please only use the searched product if you are sure of the part numbers as parts cannot be returned if ordered incorrectly.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
90008214201L
The product you are viewing cross references to these numbers