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Composite Cylinder-Head Gaskets and Damage Analysis

Composite Cylinder-head Gaskets
The classical composite head gasket is a compressible flat gasket. It consists of a tanged metal carrier sheet, onto which the composite material is rolled on both sides, i.e. engine block and cylinder head. Metal beads (fire rings) seal the combustion chamber and protect the sensitive composite material from overheating. The material surface is impregnated to prevent the gasket swelling when it comes in contact with liquid media such as oil, water, or antifreeze. So-called Viton elements of elastomer materials permit a partial increase of mounting surface pressure in the vicinity of oil pressure channels.

Classical composite head gasket with tanged metal carrier sheet, composite material rolled onto both sides, impregnation, fire rings, and Viton element.

Damage to Composite Cylinder-head Gaskets

Different Types of Leakage
Composite head gaskets are subjected to a comprehensive testing sequence. Hereby, approval for installation is only given to topquality and absolutely perfect head gaskets. Nonetheless, leaks can still occur during practical operation, but only in exceptional cases is this due to a faulty head gasket. There are numerous possible causes for damage to composite cylinder-head gaskets.

Gas, Oil, and Coolant Leaks
In professional terminology, leaks between cylinder head, head gasket, and engine block all fall under the general term «leakage». Hereby, a distinction is made between gas, oil, and coolant leakage, also known as «media leakage».

In total, seven different types of media leakage can occur with composite head gaskets:

  1. Gas leakage between combustion chambers
  2. Gas leakage from combustion chamber to coolant circuit
  3. Gas leakage to the environment
  4. Oil leakage to the coolant circuit
  5. Oil leakage to the environment
  6. Water leakage to the lubricant circuit
  7. Water leakage to the environment 

Typical media leakages with composite cylinder head gaskets.

Leakage describes a permeable point in a sealing system, through which gases or liquids can escape or enter. Leakage can cause the entire sealing system to fail.

Damage, Analysis, and Causal Investigation

Engine overheating can be due to faults in the water pump, radiator, thermostat or hoses, insufficient coolant, or incorrect venting of the coolant system after work on the cylinder head. Other causes for possible overheating are irregular combustion in the engine due to coke deposits, and high exhaust gas pressure in the case of catalytic converter failure.

When removing the head gasket, it is important to observe the manufacturer’s instructions, in order to prevent distortions of cylinder head and/or engine block. Make sure that the component sealing surfaces are not damaged during removal of the cylinder-head gasket.

Destruction in the web area due to combustion gas blowby.

Gas leakage with local blackening of the fire ring bead. Gas leakage with blackening can be the result of insufficient sealing surface pressure or an overheated engine.

Gas leakage with severe marking due to blowby of hot combustion gases.

Oil and Coolant Leakage
As opposed to gas leakage, gasket damage due to oil or coolant leakage is very difficult to detect on a composite head gasket after disassembly. Traces of rust and antifreeze agent with white, lime-like deposits on the gasket surface can be indicators for coolant leakages. Concrete evidence for oil leakage is found very rarely.

Dirt, Foreign Objects, and Rough Surfaces
Practice shows that reference to the importance of clean surfaces is necessary. Repeatedly, pressed-in dirt or foreign objects are the cause for damage and leakage. Therefore, the surfaces of engine block and cylinder head should be cleaned thoroughly. This applies in particular after reworking the surfaces in case of component unevenness, distortion, waviness (deviations in parallelism), or roughness (scores and grooves).

When installing a composite cylinder-head gasket with Viton element, make sure that the cylinder head and the head gasket are positioned accurately. Inaccurate positioning can cause the Viton element to be overpressed or it can become damaged by sharp component edges. When replacing a cylinder head gasket additional sealing compound is required only when explicitly specified by the manufacturer.

Gasket damage due to dirt and foreign objects.

Instructions in case of a damaged gasket:
  1. Before removing the head gasket, try to identify the location of the leak clearly.
  2. Analyze the damage, and determine the cause – the gasket is not necessarily the source of the problem.
  3. Remedy the cause of the damage to prevent subsequent problems.
  4. Only then is it advisable to install a new head gasket.
  5. Observe the manufacturer‘s installation instructions.

Swelling of composite cylinder-head gaskets due to overheating with steam generation.

Indentation and crushing due to pre-ignition – with and without blowby.The swelling results from the destruction of the gasket material’s silicone impregnating agent, which is not resistant to steam.

Roughness of engine block and cylinder head surfaces leads to gas blowby between the combustion chambers.

Tearing and breakage of the composite material, and damaged Viton element due to incorrect application of additional sealing compound.

Informaciones prácticas

Tips and Practical Information