Multi-layer Steel (MLS) Cylinder-Head Gaskets

Innovative Sealing Systems for New Engine Concepts

Multi-layer Steel Offers Higher Sealing Potential
MLS head gaskets consist of two to five sheets of spring or carbon steel, which are sandwiched with the sealing material to form multi-layer steel head gaskets. For improved sealing of gases and liquids, beads around combustion chambers and oil/coolant passages increase the local sealing pressure (macro sealing), whilst full-surface or partial elastomer coatings provide additional sealing tightness (micro sealing).

Typical 3-layer MLS head gasket with top sheet, active layer with Wave-Stopper, and bottom sheet beads plus full-surface (interior) and partial (exterior) elastomer coatings improve the sealing potential of these modern sealing systems. Beads for macro sealing, and elastomer coating for micro sealing.

Optimum Surface Finish for Better Sealing

Properties of Sealing Surfaces Also in future, MLS head gaskets will represent the leading sealing concept. Already today, sealing between cylinder head and engine block is achieved almost exclusively by means of multi-layer steel head gaskets. However, it is not only the head gasket‘s quality that is responsible for perfect sealing. An equally important role is played by the surface qualities of cylinder head and engine block. The demands placed on the surface finish are a decisive factor for reliable sealing results. Therefore, it is essential that the specified values are observed when installing head gaskets. Hereby, there is no difference between composite gaskets and MLS gaskets. Surface Deviations The following surface deviations lead to reduced surface qualities of cylinder head and engine block: Component unevenness Component distortion Waviness (deviations in parallelism) Roughnesses (grooves and scores)	Example of influences of surface quality due to surface deviations on an engine block. TIP The standards for the surface texture of sealing surfaces are defined in DIN EN ISO 4287. The corresponding values are Rz ≤ 15 μm for roughness, and Pt ≤ 22 μm for profile depth. Consequently, cylinder head gaskets must provide comprehensive macro and micro sealing properties.
Component Unevennesses and Distortions Component unevenness and distortion can be determined by means of a straightedge. Measurements are made using the light-gap method. The edge of the test device is placed on the surface, and moved over the bolt holes longitudinally and transversely. Hereby, any unevennesses are made visible by the light gap.

Maximum values for waviness and roughness (grooves and scores) practical measurement using a sensing probe, and indication of possible leakage channels.	Maximum values for component unevenesses and distortions for passenger cars. Practical measurement using a straightedge and the light-gap method.

MLS Head Gaskets – The Optimum Solution for Every Surface Quality

The special design of multi-layer steel gaskets enables them to adapt to every surface texture, provided that the surface quality lies within the specified tolerances.

TIP FROM THE EXPERTS

With the torque-angle tightening method, the head bolts are elongated permanently. For safety reasons, cylinder-head bolts should therefore always be used only once.

Additional data on this subject is given in our Practical Information No. 2 (Cylinder-head bolts and head installation).

TIP FROM THE EXPERTS

Be sure to observe the demands placed on surface quality:

Component unevenness for passenger cars

less than 0.03 mm over a longitudinal distance of 100 mm;

less than 0.05 mm over a longitudinal distance of 400 mm;

less than 0.03 mm over a transverse distance of 100 mm

Component unevenness for commercial vehicles

less than 0.03 mm over a longitudinal distance of 100 mm;

less than 0.10 mm over a longitudinal distance of 1,000 mm;

less than 0.03 mm over a transverse distance of 100 mm

Waviness

maximum 10 μm at wave spacing ≥ 8 mm

Roughness

Rz ≤ 15 μm
Rmax ≤ 20 μm