Engine Head Studs Cap Nut Porsche 911 1970-89  ❭  93010117201

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.