Fel-Pro Leads Engine Gasket Innovation Part 2
Part 2 of Wayne Scraba's series on high performance gaskets offers step by step install advice.
In our last issue we looked at the technology that came from Fel Pro’s well-proven PermaTorque head gaskets. Basically, this gasket configuration revolutionized how we work on high performance engines. Those gaskets eliminated a huge amount of rather ugly, tedious work. But it is important to know there is right and a wrong way to install them: When it comes to installing performance wire ring head gaskets, Fel-Pro offers this advice: “To maintain constant contact between the gasket and the sealing surfaces, the cylinder heads and engine block must start out flat and remain flat after the fasteners are torqued. On a high-performance engine, the maximum initial “out-of-flat” as measured with a straightedge and feeler gauge should not exceed 0.0025" in any direction. “Even if the cylinder heads and engine block have been milled, a straightedge should be used to verify that the surfaces are straight and true. Worn-out or improperly maintained surfacing machines can produce less-than-desirable results.” “Surface finish is critical! Having the correct surface finish on the cylinder heads and engine block is critical to a good seal. If the surface is too rough, small leak paths may result. If the surface is too smooth, it can allow excessive lateral motion of the head gasket, which can deform the combustion seal. The term most often used to describe surface finish is “Ra”, which stands for “roughness average”. It is an inverse scale – the lower the number, the smoother the finish. Surface finishes are best checked with a profilometer or surface comparator.” “When using traditional Fel-Pro Performance head gaskets, the head and block surfaces should both be in the 60-100 Ra range (400-800 Rz) for cast iron surfaces or 50-60 Ra range (200-600 Rz) for aluminum surfaces.” “Insufficient clamp load is the cause of many head gasket problems. If the gasket is not tightly clamped between the head and block, combustion gasses and engine fluids can leak past the gasket. The key to sufficient clamp load is to have adequately stretched head bolts or head studs. Proper clamp load and bolt stretch will not occur if fasteners have too much friction during assembly. When there is too much friction, torque wrench readings will reach specification before adequate bolt stretch has been achieved. Clamp load normally declines moderately over time as the head gasket “relaxes” and bolt stretch is reduced. This is measured as “torque loss” of the bolts. Clamp load can also decline due to extreme engine temperature, excessive head motion, or detonation” The bottom line with the PermaTorque gasket like is this: As racers and hot rodders, we didn’t have to go through all of the trouble of retorquing head gaskets. If you’re sufficiently seasoned (old!), you’ll recall it was painful! Fair enough, but head gaskets aren’t the only gaskets in Fel-Pro’s inventory. In fact, they have a complete range of problem solvers available. First, let’s look at header gaskets: Fel-Pro notes that the flange on an exhaust header is exposed to exhaust gas temperatures as high as 1600° F. Due to the extreme temperatures coupled with lightweight construction, flanges on headers can easily (and regularly do) warp. Factor in the nature of high performance and race engines where they’re disassembled on a regular basis, and flange warpage increases. This becomes a truly brutal environment for a gasket. In order to resolve this, Fel-Pro Performance exhaust header gaskets are manufactured with a high-density fiber facing material attached to both sides of a perforated steel core. The purpose of this technology is to resist gasket blowout and of course burnout from the extreme temperatures. That’s something a paper gasket simply can’t provide. If you have slightly warped header flanges, you might want to consider this Fel-Pro header gasket configuration. Not only that, header bolts tend to loosen over time too (particularly with paper gaskets). The high density fiber material used by Fel-Pro allows for good fastener torque retention. Something else to ponder is this: Because headers operate at temperatures hotter (often hotter) than the cylinder head, the expansion and contraction rates between the two are much different. Fel-Pro advises this causes a scrubbing motion on the gasket, which can eventually damage the gasket and cause it to fail. Fel-Pro adds an anti-stick coating on the header gaskets. This permits motion without damage to the gasket. The side benefit is, the coating makes it easier to remove the gasket when it becomes necessary. We’ll wrap this up right here and next issue, we’ll dig further into the rest of the gasket mix. When it comes to other gaskets, there’s plenty of technology available. You might be surprised at some of the problem solvers that are readily available. Watch for it! Click Here to Begin Slideshow
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