Tuesday, November 16, 2010
MLS Cylinder Head Gasket and Damage Analysis
MLS which stand for Multi-Layer Steel material of cylinder head gasket had set new standard for modern engine design. Thanks to sealing technology at the higest levels of performance and quality, they provide outstanding and efficient results under increasingly tough operating environments - the optimum preconditions for fuel-saving, environmentally compatible mobility.
Innovative cylinder head gaskets must combine utmost sealing potential with reduced bolt force losses - even with wide bolt spacing - as well as pronounced elasticity and excellent durability.
Typical leaks between cylinder head, cylinder-head gasket, and engine block involve gas, oil, or coolant leakages. These leakages occur between combustion chambers, into the coolant circuit, or to the environment. Gas leaks can result in fatal engine damage within a very short time and oil leaks can cause severe environmental pollution.
Pressed-in dirt or foreign objects as well as rough surfaces also cause damage to cylinder head gaskets. Component unevenness leads to gas blowby between the combustion chambers, and consequently to gasket failure.
Engine overheating in combination with component distortion, or inadequate compression of the cylinder head gasket are the most frequent reasons for leakage.
Thermal overloading occurs as a result of defective components in the coolant circuit or incorrect maintenance. Other causes are irregular combustion due to coke deposits, and excessively high exhaust gas pressure after failure of the catalythic converter. Moreover, chemical additives in the coolant and low-quality antifreeze agents can attack sealant coatings.
While reworking the surfaces of cylinder head or engine block in case of component unevennness, distortion, waviness, or scores and grooves, dirt and foreign objects accumulate, which can result in damage to the cylinder head gasket. Therefore, thorough cleaning of the sealing surfaces is essential before installing the cylinder head gasket.
Damage to MLS cylinder head gaskets mostly involves two sealing elements: beads and elastomer coatings. The beads can fracture due to various factors, and elastomers can become detached from the substrate material or be scorched. Both of these damage profiles indicate different causes.
Possible causes for excessively high component dynamics are faulty, reused, or unlubricated cylinder head bolts; incorrect bolt torquing due to excessively high friction during installation; and damage to cylinder head or engine block. Component distortions can also be the result of engine overheating. Similarly, if an engine is operated under pinging condition (pre-ignition), the high temperatures and pressures can lead to higher component dynamics and possible bead factures.
Calssical causes for overheating are defects of the water pump, radiator, thermostat or hoses, but also insufficient coolant system can lead to thermal problems. Failure of the catalytic converter can also result in higher temperatures due to increased exhaust back pressure.
During so-called blowby, combustion gasses flow from one cylinder to the other via the web, or from a combustion chamber into the coolant circuit. This gas flow "scorches" the elastomer or the elastomer coating in the afected area. The resulting lack of micro sealing leads to disturbances in the combustion process and reduced performance - and to a possible pressure build-up in the coolant circuit. Causes for blowby are excessively high combustion pressures, rough sealing surfaces, component distortions, or inadequate compression of the cylinder head gasket.
Contact with antifreeze agents that have not been approved can cause the elastomer coating to become detached from the metal surface, Subsequently, the dislodged elastomer particles can clog the coolant channels and interrupt the collant flow. The result is an overheating engine.
Other typical damage profiles for MLS cylinder head gaskets are destroyed combustion chamber seals due to incorrect cylinder liner protrusion or faulty liner flange seats, as well as severely damaged Ricardo squish areas due to detached swirl cambers.