Crankshaft Main Bearing O-Ring, 51x 4.5. Porsche 911 78-89 / 964 / 993 / 996 Turbo / 997 Turbo / GT3  ❭  99970728541

Crankshaft Main Bearing O-Ring, 51x 4.5
The Genuine Porsche 99970728541 crankshaft main bearing O-ring is an OE 51 x 4.5 mm sealing ring for selected Porsche flat-six engine applications, including 911 1978–1989, 964, 993, 996 Turbo, 997 Turbo and GT3 models. It seals the crankshaft main / nose bearing area, helping prevent oil leaks and maintain proper engine sealing. Ideal for engine rebuilds, crankshaft service or replacing a hardened, flattened or leaking original O-ring.
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Fits:
Porsche 911 1978 - 1989
Porsche 964 1989 - 1994
Porsche 993 1995 - 1998
Porsche 996 Turbo 3.6L 2001 - 2005
Porsche 996 GT3 3.6L 1999 - 2005
Porsche 997.1 Turbo 3.6L 2007 - 2009
Porsche 997.2 Turbo 3.6L 2010 - 2013
Porsche 997 GT3 3.6L / 3.8L / 4.0L 2007 - 2011

Diagram ref no 21

This O-ring is used in the crankshaft / main bearing sealing area on selected Porsche flat-six engines.

What This Part Does / Functions
•  Seals the crankshaft main / nose bearing area
•  Helps prevent engine oil leakage
•  Supports correct crankshaft bearing housing sealing
•  Helps maintain engine oil pressure and lubrication integrity
•  Provides correct OE Porsche size, material and fitment
•  Replaces a flattened, hardened, cut or leaking original O-ring
•  Supports correct reassembly during engine or crankshaft service
•  Helps maintain factory engine sealing performance.

Why Replace This Part?
Engine O-rings are exposed to oil, heat, pressure, age and compression. Over time, the rubber can harden, flatten, crack or lose elasticity. Once disturbed during engine disassembly, the O-ring should normally be replaced to ensure a reliable seal when reassembled. Replacing it with a Genuine Porsche OE crankshaft main bearing O-ring helps prevent oil leaks and ensures the engine is rebuilt with the correct factory sealing component.

Common Symptoms of a Failed O-Ring
•   Oil leakage from the crankshaft / main bearing area
•   Oil residue around the crankshaft housing
•   Persistent seepage after previous engine work
•   Hardened, flattened or cracked O-ring during inspection
•   Loss of sealing after engine disassembly
•   Oil leaks following crankshaft or bearing housing service.

When to Replace This Part
•   During engine rebuild or overhaul
•   When servicing the crankshaft main / nose bearing area
•   If the O-ring is hardened, flattened, split or damaged
•   If oil leakage is traced to the crankshaft bearing seal area
•   Whenever the relevant crankshaft bearing housing is removed
•   During gearbox-side or crankshaft sealing work where specified
•   When restoring the engine with correct Genuine Porsche sealing parts
•   Whenever Porsche workshop procedure recommends replacing the O-ring after removal.

Where It Fits on the Car
This O-ring fits in the engine crankshaft main / nose bearing sealing area. It forms part of the engine sealing arrangement around the crankshaft bearing housing and helps prevent oil from escaping through the joint. Correct installation is important. The sealing surfaces should be clean, and the O-ring should be installed without twisting, pinching or damage


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99970728541

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