By Titus Bloom:
SCE Gaskets, headed by Ryan Hunter, recently introduced a new line of MLS (multi-layered steel) cylinder head gaskets that extend to 14 applications with plans to expand LS coverage and to penetrate the Ford Modular ranks.
The starting point, he explains, involves forming embossments in the outer stainless steel plates. “The coolant seal is a less aggressive ‘Z’ shape; combustion seal is formed into an inverted ‘U’ shape capable of sealing much higher pressures. My job as a gasket designer,” Hunter says, “is to calculate the clamp load generated by the total number of cylinder head bolts and direct it to where it needs to go, seal embossment shape is a key part of that process.
“Combustion pressures are typically between 1600 and 1800psi in a naturally aspirated high performance engine, but less than half-inch away I’ve got 22 to 45psi coolant pressures. In round numbers, 10 head bolt fasteners generate around 100,000lb of total clamp load. What I need to do is to make 60,000lb available to seal the combustion pressures—thereby devoting 40 percent of the clamping pressure to coolant sealing.”
The manufacturing process for the MLS gaskets is thus: embossing the sealing areas, cutting to shape and then stress-relieving. If stress relieving isn’t executed at this stage, the embossments tend to revert to their original shape. Stress relieving after forming normalizes the stainless steel plates in their embossed shape resulting in increased spring pressure against the block and head at the seal location. The increased spring pressure – or memory – retains seal integrity during lateral movement between cylinder head and block that occurs particularly with dissimilar metals. Temperature changes—expansion rates from cold to hot—between a cast-iron block and an aluminum cylinder head can differ by a factor of 100 percent.
SCE began developing their coating process in a partnership initiated in 2011. The process combines a two-part polymer, which is applied after the forming and stress relieving operations. “If you apply the coating process before embossing,” explains Hunter, “inconveniently, the coating thickness becomes reduced and weakened over the embossed areas.”
The concept of multi-layer gaskets, explains Ryan Hunter, was first introduced by the Japanese in the early nineteen nineties. “Initially they required an extremely smooth finish on the block and cylinder heads, between 15 and 30Ra,” he says. “Of course, this could be accomplished by the original equipment manufactures that operate with almost unlimited budgets, but not so the aftermarket. Today, our gaskets with highly developed sealing compounds will seal up to 60Ra.”
Note: For a visual Ra comparison, consider the mirror-finish of a crankshaft journal which is usually about 12Ra.
To download SCE’s flyer on their new line of MLS gaskets click here.
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