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.

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Related, superseded, cross reference or alternative numbers for comparison.

90110438204

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Cylinder head stud. Porsche 912 / 356B / 356C



Fits:
Porsche 912
Porsche 356 B
Porsche 356 C

Click 'Zoom in' for large parts diagram.
Diagram ref no 2

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53901118

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Cylinder head studs
This OE Match cylinder head stud is a replacement engine fastening stud for Porsche 911, 964, and 993 models from 1965 to 1998. It is designed to match the original-style fitment and function, helping secure the cylinder head and cylinder assembly correctly to the engine crankcase.  
Sold individually, Normally 24 studs per engine

Fits:
Porsche 911 1965 - 1989
Porsche 964 1989 - 1994
Porsche 993 1994 - 1998

This product supersedes Porsche's old part numbers:
- 99310117051

Diagram Ref No 2.

The cylinder head stud provides the clamping force needed to hold the cylinder head, cylinder barrel, and engine case together. Correct head stud tension is essential for maintaining combustion sealing, cylinder stability, and reliable air-cooled engine operation.

Functions
• Secures the cylinder head and cylinder assembly to the engine case
• Provides correct clamping force for combustion sealing
• Supports cylinder and head alignment
• Helps maintain reliable engine sealing under heat and load
• Replaces corroded, stretched, broken, or damaged original studs
• Suitable for engine rebuilds, top-end repairs, and head stud replacement
• OE Match replacement for classic Porsche air-cooled engine repair

Why Replace This Part?
Cylinder head studs are exposed to high combustion forces, heat cycling, corrosion, vibration, and long-term engine load. Over time, studs can corrode, stretch, weaken, seize, or break. A damaged or broken head stud may cause compression leakage, oil seepage, cylinder head movement, exhaust leakage, poor running, or engine noise. Replacing worn or failed studs helps restore proper engine clamping and long-term reliability.

When to Replace This Part
•  A cylinder head stud is broken, corroded, stretched, or damaged
•  The engine has compression leakage or cylinder head sealing issues
•  Oil seepage or combustion leakage is present around the cylinder/head area
•  The engine is being rebuilt or overhauled
•  The cylinder heads or barrels have been removed
•  Existing studs are seized, heavily corroded, or unsuitable for reuse
•  Preventative replacement is being carried out during top-end service.

Where it fits on the car
This cylinder head stud fits within the engine crankcase and extends through the cylinder barrel and cylinder head assembly. It forms part of the engine’s main cylinder/head fastening system and should be installed according to the factory engine layout and torque procedure.

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

99310117054

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Dilavar Head Studs.
Normally 24 studs per engine. Sold EACH



Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1994-98

This product supersedes Porsche's old part numbers:
- 99310117051

Solves the problems of loose head studs, The exhaust leak you hear in the 911 may actually be the cylinder head leaking where the studs have pulled loose. As Porsche increased displacement of the 911 engine, the different rates of thermal expansion have caused head studs to break or pull out from the engine case. These latest Dilavar steel head studs have a thermal expansion rate of approximately the same as the alloy case.

Click 'Zoom in' for large parts diagram.
Diagram Ref No 2.

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

99310117054

The product you are viewing cross references to these numbers

Dilavar head studs.
Dilavar engine head studs are specialized fasteners used in the engines of certain Porsche models, especially air-cooled engines (like the 911). They are made from a proprietary alloy called Dilavar, which is designed to address specific thermal expansion and durability challenges in high-performance engines.
Price is each. Normally 24 studs per engine. 

Fits:
Porsche 911 1965 - 1989
Porsche 964 1989 - 1994
Porsche 993 1994 - 1998

Diagram Ref No 2.

This product supersedes Porsche's old part numbers:
- 99310117051

Solves the problems of loose head studs, The exhaust leak you hear in the 911 may actually be the cylinder head leaking where the studs have pulled loose. As Porsche increased displacement of the 911 engine, the different rates of thermal expansion have caused head studs to break or pull out from the engine case. These latest Dilavar steel head studs have a thermal expansion rate of approximately the same as the alloy case.

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

99310117054

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Engine case through bolt set, titanium. 

Kit Contents
Ti Alloy Studs x 11
Ti Alloy Washers x 22
Ti Alloy 12-point Nuts x 11

Porsche Motorsports employed titanium alloy engine case fasteners on many of their famous race cars, including the 904, 908, 935, 962, and some modern LMP2.

Fits:
Porsche 911
Porsche 964
Porsche 993

Air-cooled Porsche 911 engine case through bolts in high-strength high-purity Titanium alloy. Including studs, washers, and  nuts.

Related reference numbers
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SL-TB-

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Engine crankcase stud M8 X 78. 3 per engine. Price is for each.



Fits:
Porsche 911 1965-89 all models
Porsche 964 1989-94
Porsche 993 1995-98
Porsche 996 TURBO / GT3 1998-04
Porsche 997 TURBO / GT3 2005-12
Porsche 914 1970-76


Click 'Zoom in' for large parts diagram.
Diagram Ref No 6.

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90006010101

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Engine crankcase stud, BM 10 X 85.



Fits:
Porsche 911 1965-73
Porsche 911/911S / Carrera 2.7 1974-77
Porsche 914-6 1970-76

Click 'Zoom in' for large parts diagram.
Diagram ref no 16

Related reference numbers
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99906221701

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Engine crankcase stud, BM8FO x 22. 
Sold each.



Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1995-98
Porsche 996 Turbo 2001-05
Porsche 996 GT3 3.6L 1999-05
Porsche 997.1 Turbo 2007-09
Porsche 997 GT3 3.6L 2006-09
Porsche 914-6 1970-76

Click 'Zoom in' for large parts diagram.
Diagram ref no 4

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

90006010601

The product you are viewing cross references to these numbers

Engine crankcase stud, BM8FO x 22. 
Sold each.



Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1995-98
Porsche 996 Turbo 2001-05
Porsche 996 GT3 3.6L 1999-05
Porsche 997.1 Turbo 2007-09
Porsche 997 GT3 3.6L 2006-09
Porsche 914-6 1970-76

Click 'Zoom in' for large parts diagram.
Diagram ref no 4

Related reference numbers
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90006010601

The product you are viewing cross references to these numbers

Engine crankcase stud, M8 x 52. RIGHT.
Sold each.



Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1995-98
Porsche 996 Turbo 2001-05
Porsche 996 GT3 3.6L 1999-05
Porsche 997.1 Turbo 2007-09
Porsche 997 GT3 3.6L 2006-09
Porsche 914-6 1970-76

Click 'Zoom in' for large parts diagram.
Diagram ref no 11

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90006010201

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Head stud height setter for Porsche 911



Precisely set the height of head studs on all the 911 engines using this innovative tool. The Delrin insert protects the engine case from scratches or marring, while the adjustable three-piece anodized aluminium tubular construction provides complete flexibility for all engine setups, tools, and stud combinations.

For all 911s including GT3s.

Engine Head Studs Porsche 911 / 964 / 993 1965-98
Normally 24 studs per engine.

Solves the problems of loose head studs, The exhaust leak you hear in the 911 may actually be the cylinder head leaking where the studs have pulled loose. As Porsche increased displacement of the 911 engine, the different rates of thermal expansion have caused head studs to break or pull out from the engine case.

Superior Tested/Proven strength. (compared to Dilavar & Raceware)

Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1994-98

This product supersedes Porsche's old part numbers:
- 993 101 170 51

Click picture for large parts diagram.
Diagram Ref No 2.

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

99310117054

The product you are viewing cross references to these numbers

Engine case studs.
24 per engine. Price is for each.

Fits:
Porsche 911 1965-73
(Not 1973 2.7L Carrera)
Porsche 914-6 1970-72

Diagram ref No 5

Related reference numbers
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90110117203

The product you are viewing cross references to these numbers

Engine case studs.
24 per engine. Price is for each.

Fits:
Porsche 911 1965-73
(Not 1973 2.7L Carrera)
Porsche 914-6 1970-72

Diagram ref No 5

Related reference numbers
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90110117203

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Engine head studs. Set of 24 head studs with nuts and washers.

SET OF 24
Head stud kit for Porsche 2.0L-3.8L air-cooled engines

Fits:
Porsche 911 1965-89
Porsche 964 1989-94
Porsche 993 1994-98

Diagram Ref No 2

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

99310117054

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