By Titus Bloom:
Originating at the turn of the nineteen-nineties, the unorthodox MLS gasket shook the establishment. Complex and revolutionary by comparison to its forerunner, its fundamental difference was its multi-layer construction—usually consisting of at least three layers.
Kentucky-based World Products engine designer, Dick Boyer, says “MLS offer several significant advantages, particularly when situated between two different materials. Dissimilar metals, like a cast-iron block and cast aluminum cylinder head, for example, expand at different rates and the MLS gasket allows more movement than the conventional-style head gasket, because of its multi layer construction.” The conventional gasket is typically composed of a single steel core with paper gasket material attached.
The inner portion of the MLS, which is made of stainless steel, serves to provide the finished gasket thickness. It also acts as the layer on which the top and bottom layers press against and, importantly, it contributes to the gasket’s sealing properties.
The outer layers, which are also made of tempered stainless steel, feature raised beads or embossments that encircle critical sealing areas particularly the combustion openings and water jacket ports. The spring steel raised beads of the upper and lower layers resist flattening and it is this spring pressure that creates the seal, particularly when the engine is operating. Race engine builder Jon Kaase refers to the unique quality of the MLS gasket as “its springiness”.
Unlike the conventional gasket, which cannot expand and contract, the MLS has spring tension when fastened to the correct torque loading. This allows the gasket to relax and compress as the cylinder head tends to move up and down slightly while the engine is operating. And it’s here, in the sealing of the combustions gases of high performance and competition engines, where JE specializes.
Today, there is an abundance of MLS gaskets available, but most brands have their limitations. It is much more difficult to make your mark at the highest levels of competition gasket-making if you have no serious experience in cylinder sealing.
Now based in Cleveland, Ohio, JE honed its craft in the development of competition pistons and piston rings where cylinder sealing is crucial. In the construction of competition MLS gaskets they brought a fresh new presence to the process.
What’s different about the competition MLS head gasket?
There’s much more to the construction of a MLS competition gasket than you might realize. Sealing combustion pressures on competition engines, which often exceed 1,200psi, requires paying close attention to the type of stainless steel used, the heat treatment process employed, the embossing procedures and the special polymer coatings applied.
If the stainless steel is too soft or too hard the MLS gasket will fail. For this reason JE opts for AISI 304 stainless and combines it with a proprietary heat treatment. On the central layer of a three-layer gasket or the second layer from the top of a four-layer assembly, they incorporate a folded “stopper” layer to increase surface pressure around the cylinder openings.
Importantly, the embossments around the cylinder openings and water jacket ports on the top and bottom layers are not formed rapidly in a single operation, but instead shaped slowly in multiple stages. From the gasket edge to the start of the embossment, JE incorporates a minimum inner flange spacing of 0.040in.
Some MLS gaskets use a single layer sealing compound on their upper and lower surfaces. But JE insists on multiple layers for racing engines. They use a material known as fluoroelastomer (FKM), a special purpose fluorocarbon-based synthetic rubber with Viton. After the coatings are applied the layers are hand-assembled.
The importance of deck finish
Dick Boyer of World Products says, “The profilometer is useful, but measuring the scratch depth in a deck surface is usually of less consequence than wave finish. You can have a beautifully smooth surface with a potentially threatening wave depth of 0.002in or 0.003!”
How do you check wave finish?
“We lay a granite plate with 300-grit sandpaper on the deck of the block and stroke it five times front to rear—you’ll see the high spots, you’ll see the wave, which we measure with an indicator. We limit variations in wave depth to 0.001in. It’s easy to control the prolifometer readings; it’s less easy to control the wave.”