Everything You Need To Know About Modern Gaskets: Part 2

Component prep is important when it comes to using MLS head gaskets. Both the block deck and the deck surface of the cylinder heads must be machined so that they are flat and parallel to the centerline of the crankshaft.

Everything You Need To Know About Modern Gaskets: Part 2

Click Here to Begin Slideshow

We began this series with a detailed look at the modern head gaskets offered by the folks at Mahle Performance. If you spin your browser back to (Part 1), you’ll gain insight into Mahle’s MLS technology. And since MLS gaskets are very different when compared to older composite gaskets, engine prep and gasket installation differ too.

Something to ponder is this: The cylinder block and cylinder head prep for an MLS gasket is very important. Think about it as the foundation for sealing the combustion process. Typically, both the block deck and the deck surface of the cylinder heads should be machined so that they are flat and parallel to the centerline of the crankshaft. Some folks suggest an out-of-flatness range of between 0.002-inch to 0.004-inch over a span of a V8 deck, and 0.002-inch for the width of the deck (cylinder block and cylinder head).

The decks must also have an extremely smooth surface. They must be free of scuffs, scratches, corrosion and of course, cracks in order to avoid combustion leakage. Most of today’s machine shops can accomplish this easily, but you must always keep in mind that MLS gasket should never be used on a pitted, worn, or roughly machined surface.

There are two measurements of surface roughness you have to consider when it comes to deck finishes. These are measured in micro-inches or “µin”. A micro-inch is the measurement unit of length or distance, and equal to one millionth of an inch (0.000001 inch). “Ra” is the roughness average in height, while “Rz” is the peak-to-valley roughness average in height. Typically, a composite gasket performs well with surfaces ranging from 60-80 Ra (360-480 Rz). Basically, if the surface is rougher, then the gasket will have difficulty conforming. On the other hand, MLS head gaskets mandate much smoother surface finishes. Early MLS gaskets required a surface finish or 30 Ra or smoother. Today, however the typical MLS gasket can function properly with a 40-60 Ra (180-480Rz). Although different manufacturers have different specifications, smoother deck surfaces are always superior when it comes to modern head gaskets. And by the way, it’s not uncommon today to find aftermarket cylinder heads that come out of the box with surface finish levels of 60 RA (or so).

One more consideration when prepping an engine for MLS head gaskets is the fact they do not work with block or head O-rings. Some folks suggest the O-ring grooves must be removed by surfacing, but in many cases, that’s asking a lot. Others suggest you can get away with it provided the O-ring groove is outboard of the fire ring on the gasket. The best scenario though, is to start the build with a non-O-ringed block and/or cylinder heads.

What about MLS head gasket installation? First things first: No additional coatings are necessary although some folks use a tiny (thin) application of silicone on both sides of the head gasket coolant passage “ear” (see the accompanying photo). The reason for this is, the “ear” area on the gasket is often unsupported, and there’s a chance it can seep coolant.

What about copper coat head gasket spray? It was used with regularity on old school steel head gaskets. Basically, the purpose of the copper spray was to fill in surface irregularities in either/or the head gasket deck and block deck surfaces. But that was then. The spray can actually prove detrimental to the performance of an MLS head gasket. The reason is, the sealers can get in between the layers of an MLS gasket, which in turn can create a path for leakage (combustion, coolant or oil). Additionally, sealants used on an MLS head gasket can actually provide for a false torque wrench reading. By the way, the fluorelastomer coating used by Mahle allows the gasket to conform to any surface irregularities. It does a far better job than any of the old copper coat sprays used in the past. Just remember to keep the deck surfaces clean.

Another common question is: “Can MLS head gaskets be reused?” The short answer is no. But you might see some pro racers reusing them. The reason here is, something like a Pro Stock engine is torn down regularly. If the fluorelastomer coating on both sides of the gasket looks fine, then the race team figure they can get away with it. For a little guy, it might not be worth the risk.

As we all know, cylinder head gaskets are only a part of the engine puzzle. In an upcoming issue of RacingJunk.com, we’ll expand our series, beginning with header gaskets. And just like cylinder head gaskets, there’s some surprising technology available. In the meantime, check out the accompanying head gasket tech slideshow:


MAHLE Aftermarket Inc.
23030 MAHLE Drive, Farmington Hills, MI 48335
Phone: (800) 338-8786
Website: Mahle Performance
Click Here to Begin Slideshow

Everything You Need To Know About Modern Gaskets: Part 2

Component prep is important when it comes to using MLS head gaskets. Both the block deck and the deck surface of the cylinder heads must be machined so that they are flat and parallel to the centerline of the crankshaft.

Everything You Need To Know About Modern Gaskets: Part 2

Additionally, they must be extremely smooth, free of scuffs, scratches, corrosion. See the text for details.

Everything You Need To Know About Modern Gaskets: Part 2

Sealants should not be used on a Mahle head gasket. The only exception is this “ear” area on the gasket. It is often unsupported, and there’s a chance it can seep coolant. The solution is to use a tiny (thin) application of silicone on both sides of the ear.

Everything You Need To Know About Modern Gaskets: Part 2

Like many other types of head gaskets, MLS gaskets are really not designed to be reused. There are a few select exceptions for most of us, it’s important to use fresh gaskets following a rebuild.

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