Engine Bolts / Studs

Cylinder Head Nut 
Sold each - 24 required for the 911

Maintain the integrity and reliability of your Porsche engine rebuild with this OE Match Cylinder Head Nut 90110438204. Designed for use on Porsche 356B, 356C, 912 and classic 911 air-cooled engines, this precision-engineered fastener plays a critical role in securing the cylinder head assembly to the engine.

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)
• Porsche 356B 1959-63
• Porsche 356C 1963-65

Diagram Ref No 17

Although small in size, cylinder head nuts are among the most important fasteners in any engine. They provide the clamping force required to maintain an effective seal between the cylinder heads, cylinders and engine case, ensuring correct compression, combustion efficiency and long-term engine reliability.

Manufactured to OE Match specifications, this cylinder head nut is ideal for engine rebuilds, top-end overhauls, cylinder head refurbishment and concours restorations.

What Does a Cylinder Head Nut Do?

The cylinder head nut secures the cylinder head assembly to the engine using the cylinder head studs.

Its primary functions include:

• Maintaining cylinder head clamping force
• Ensuring correct cylinder sealing
• Supporting combustion chamber integrity
• Maintaining engine compression
• Preventing cylinder head movement
• Supporting reliable engine operation
• Helping prevent oil and combustion leaks

Correct clamping force is essential for maintaining engine performance and durability.

Why Do Cylinder Head Nuts Fail?

Cylinder head nuts are exposed to repeated heat cycles, vibration and engine loads throughout their service life.

Common causes of deterioration include:

• Corrosion
• Thread wear
• Fatigue from repeated heat cycles
• Over-tightening
• Incorrect installation procedures
• Engine overheating
• Age-related degradation
• Damage during previous rebuilds

In older air-cooled Porsche engines, decades of service can leave original hardware weakened or unsuitable for reuse.

Symptoms of Worn or Damaged Cylinder Head Hardware

Potential warning signs include:

• Loss of cylinder sealing
• Compression leaks
• Oil seepage around cylinder heads
• Difficulty achieving correct torque settings
• Damaged threads
• Corroded hardware
• Uneven clamping loads
• Engine rebuild inspection failures

Many of these issues are discovered during engine disassembly rather than during normal operation.

When Should Cylinder Head Nuts Be Replaced?

Replacement is strongly recommended when:

• Rebuilding an engine
• Carrying out a top-end overhaul
• Replacing cylinder head studs
• Refurbishing cylinder heads
• Corrosion is present
• Threads show signs of wear
• Factory specifications require replacement

Most professional Porsche engine builders replace critical fastening hardware during major engine work to ensure long-term reliability.

Why Replacement Matters

Reusing worn or damaged cylinder head hardware can compromise engine sealing and reliability.

Benefits of replacement include:

• Correct clamping force
• Improved sealing performance
• Reduced risk of leaks
• Improved engine reliability
• Professional rebuild standards
• Long-term durability
• Factory-correct restoration quality
• Greater peace of mind

For classic Porsche engines, replacing critical hardware is inexpensive insurance against future engine issues.

The OE MATCH Cylinder Head Stud is a replacement engine fastening component designed to maintain secure cylinder head installation and reliable engine sealing on classic Porsche 356B, 356C and 912 models.

• Porsche 912
• Porsche 356 B
• Porsche 356 C

Manufactured to match the original equipment design and specifications, this cylinder head stud forms an essential part of the engine's cylinder head retaining system, providing the clamping force required to hold the cylinder head and associated engine components securely in position.

The air-cooled four-cylinder engines fitted to the Porsche 356 and 912 operate under demanding conditions involving high combustion pressures, engine vibration and continuous temperature fluctuations. Maintaining correct cylinder head clamping is essential for preserving compression, preventing combustion gas leakage and supporting reliable engine performance.

The cylinder head stud works together with the appropriate retaining nuts and associated fastening hardware to maintain the intended compression and sealing between the cylinder head and cylinder assembly.

During normal engine operation, the cylinder head and surrounding components repeatedly expand and contract as temperatures rise and fall. The retaining studs must withstand these thermal cycles while maintaining sufficient clamping force to prevent unwanted movement or loss of sealing integrity.

Over time, original cylinder head studs can deteriorate due to corrosion, prolonged thermal exposure, mechanical fatigue, incorrect tightening or previous engine repairs. Worn, stretched, damaged or broken studs may reduce the clamping force applied to the cylinder head, potentially resulting in compression leaks, combustion gas leakage and increased mechanical stress on surrounding components.

Replacing a damaged or weakened cylinder head stud with an OE MATCH component helps restore the original fastening arrangement, maintain reliable cylinder head sealing and protect the engine against further damage.

Ideal for Porsche 356 and 912 engine rebuilding, cylinder head repairs, top-end overhauls and classic Porsche restoration projects.

What This Product Does:
The cylinder head stud is an essential mechanical fastening component within the engine assembly.

Its primary functions include:

• Secures the Cylinder Head: Provides the threaded fastening arrangement required to hold the cylinder head securely against the cylinder assembly.
• Maintains Cylinder Head Clamping Force: Works with the appropriate retaining nuts to maintain the specified clamping load.
• Supports Combustion Chamber Sealing: Helps maintain a secure connection between the cylinder head and cylinder to prevent combustion gases from escaping.
• Maintains Engine Compression: Supports the sealing integrity required for consistent cylinder compression.
• Prevents Unwanted Cylinder Head Movement: Helps keep the cylinder head correctly positioned during engine operation.
• Withstands Engine Temperature Changes: Accommodates the mechanical stresses caused by repeated heating and cooling cycles.
• Resists Combustion Forces: Helps maintain secure head retention under the high pressures generated during combustion.
• Supports Engine Structural Integrity: Contributes to the secure assembly of the cylinder head, cylinder barrel and associated engine components.
• Protects Engine Components: Helps reduce the risk of damage caused by loose or incorrectly secured cylinder heads.
• Maintains Original Equipment Configuration: Replaces the original fastening component while preserving the factory-style cylinder head assembly.

Over time, these conditions can contribute to corrosion, thread damage, fatigue or mechanical failure.

Common symptoms of a worn, damaged or failing cylinder head stud include:

• Broken or Fractured Stud: The stud may snap or fracture due to fatigue, excessive stress or incorrect installation.
• Loose Cylinder Head: A damaged stud may prevent the cylinder head from maintaining the required clamping force.
• Loss of Engine Compression: Inadequate head clamping can allow combustion pressure to escape from the cylinder head sealing area.
• Combustion Gas Leakage: Escaping combustion gases may produce a distinctive ticking, puffing or chuffing noise around the cylinder head.
• Oil Seepage Around the Cylinder Head: Reduced clamping or associated sealing problems may contribute to oil leakage around the cylinder head or related components.
• Damaged or Stripped Threads: Thread wear may prevent the retaining nut from tightening correctly.
• Corroded Cylinder Head Studs: Severe corrosion can weaken the fastener or make removal difficult.
• Stud Stretching or Deformation: Excessive tightening or mechanical overload may permanently deform the stud.
• Difficulty Maintaining Correct Torque: Damaged threads or weakened fasteners may prevent correct tightening during engine assembly.
• Uneven Engine Running: Significant compression loss may contribute to rough idling, reduced power or inconsistent combustion.
• Unusual Engine Noises: Combustion leakage or movement around the cylinder head may cause abnormal engine noises.
• Visible Damage During Engine Rebuild: Inspection may reveal corrosion, thread deterioration, cracks or signs of previous overstressing.
• Damaged Crankcase Threads: A stud that has loosened or pulled from its mounting position may indicate damage to the threaded crankcase connection.

Key Benefits of Replacement:

• Restores Cylinder Head Retention: Replaces damaged studs to help maintain secure cylinder head installation.
• Maintains Correct Clamping Force: Supports the specified fastening load required for reliable cylinder head sealing.
• Helps Prevent Compression Leaks: Maintains the correct clamping arrangement between the cylinder head and cylinder.
• Protects Against Combustion Gas Leakage: Reduces the risk of escaping combustion gases caused by inadequate head retention.
• Supports Consistent Engine Performance: Helps preserve the compression and sealing conditions required for smooth engine operation.
• Reduces Mechanical Stress: Helps prevent unwanted movement that may damage cylinder heads, cylinders or associated components.
• Protects Engine Reliability: Reduces the risk of further damage caused by a loose or improperly secured cylinder head.
• Replaces Damaged Threads: Restores reliable fastening where the original stud is corroded, stripped or otherwise unsuitable for reuse.
• Original Equipment-Style Fitment: Designed to match the corresponding Porsche engine fastening arrangement.
• Suitable for Engine Rebuilds: Ideal when replacing worn engine fastening components during a complete rebuild.
• Supports Top-End Overhauls: Provides the correct replacement component when cylinder heads are removed for servicing.
• Helps Prevent Expensive Engine Repairs: Addressing damaged cylinder head hardware promptly may prevent further mechanical damage.
• Maintains Classic Porsche Originality: Preserves the original fastening arrangement used on the applicable air-cooled four-cylinder engines.

Although the cylinder head stud is a relatively small component, it performs a critical function in maintaining the structural integrity of the engine.

A broken or damaged stud may reduce the clamping force holding the cylinder head in place, potentially allowing combustion gases to escape and affecting engine compression.

Continued operation with a loose or incorrectly secured cylinder head can increase thermal and mechanical stress on surrounding components, leading to further damage.

Replacing a defective stud with an OE MATCH component helps restore the specified fastening arrangement and supports dependable engine performance.

During engine rebuilding, all cylinder head studs should be inspected carefully. Where multiple studs show signs of corrosion, thread damage or fatigue, replacing the affected fasteners may be advisable to maintain consistent assembly integrity.