Some interesting tidbits from the FP brochure on MSL gaskets:
1. Surface finishing is a critical step for MLS installation.
Traditional OE type MLS gaskets are constructed of layers of very hard stainless steel. They don’t easily conform to surface irregularities, so a very thin, fairly hard, rubber coating and an incredibly smooth surface finish are required to provide a satisfactory seal. When the castings are new and the finish is fresh, most MLS gaskets work quite well, but when the castings are old, or if they are refinished with less than a perfect finish, leaks usually result.
To seal under these adverse conditions, Fel-Pro® has developed PermaTorqueMLS.™ These new redesigned MLS gaskets have many unique features to seal better than any other gasket on the market today.
2. PermaTorqueMLS™ offers specialized coating designed for the repair environment.*
Select PermaTorqueMLS gaskets feature a special coating specifically formulated for the aftermarket’s repair environment. While most MLS gaskets require a surface smoother than 40 Ra (400 Rz), these Fel-Pro PermaTorqueMLS head gaskets will seal
a surface finish as rough as 60 Ra (600 Rz). Regardless of the brand of MLS gasket chosen, for the gasket to seal properly, the finish on the head and block must be flatter and smoother than what has traditionally been required for composite gaskets.
3. Consult your machine shop for specific surface finish capabilities.
Resurfacing a head or block doesn’t necessarily guarantee flatness or the proper surface finish. Newer resurfacing equipment has the capability to produce very smooth, flat surfaces, that are well within the required roughness specs. Older, or improperly maintained equipment often leaves a less than desirable surface finish, and will often result in leakage. It is therefore extremely important to measure the roughness of the
finish produced by a particular resurfacing machine to make sure it is within specifications.
Surface finish roughness is measured in microinches (millionths of an inch) either by the “Ra” method (average of all profile points), or “Rz” (height distance from peak to valley). The only way to accurately measure the finish is to use a special instrument called a surface profilometer. This hand-held electronic instrument (which can cost from $1200 to $4000 or more) drags a diamond-tipped stylus across the surface to measure and calculate its texture.
Two other surface finish conditions that need to be examined are waviness and flatness. Waviness describes the undulations or waves across the surface of the metal which are usually associated with milling machines. A waviness height of up to .0005" (500 µin) is OK, provided the distance from peak to peak is greater than .030." It’s also important that there be no scratches or dings in the surface that exceed .001" (1000 µin). The flatness of both the head and block should always be checked with a straightedge before installing a new head gasket. Place the straightedge on the face of the cylinder head or block, and then use a feeler gauge to check any gaps between the straightedge and the surface. If the clearance between the straightedge and surface exceeds the following maximum
limits, the head or block is not flat enough to hold a good seal and should be resurfaced. The chart on this page gives you the specs that should be followed.
I'm guessing that the surface roughness thing might come into play for some of these sealing issues. My engine guy ("Bad as L" here) actually surface ground the decks vurra purty and smooth
lol
TurboTR
