In marine engines—four strokes or two-strokes—head gaskets serve the exact same function as in non-marine head gaskets, such as car engine head gaskets. Though there are differences between marine and non-marine head gaskets. The primary issues determining these differences are the environment of a marine engine, the method of cooling the engine and the source of the coolant.
What is The Function of a Head Gasket?
In any internal combustion engine, the function of head gasket is the same. It seals the head or "top end" of the engine to the block or "bottom end" of the engine. Where the head mates, the metal surfaces are milled flat, but even with precise machining, there are imperfections in the surfaces. And it is a mechanical connection, attached with stud bolts and nuts; it's not a solid piece of metal, yet it must function as if it were solid—containing all the force exerted by combustion. In fact, should this seal between head and block fail, it may cause catastrophic engine damage.
What Causes a Head Gasket to Fail?
The most common cause of failure is overheating. Any malfunction in the cooling system can cause overheating, leading to the expansion of metal parts and head gasket failure. Another common cause is detonation or "pre-detonation" where combustion in the cylinders happens before it is suppose to, creating massive stress on the engine.
Head Gasket Composition
While the function is always the same—to fill machine imperfections and provide a strong seal—there are a variety of materials and designs of head gaskets. A long list of synthetic and natural materials, such as rubber has been used. Pure metal, such as a copper sheet, die cut to the shape of the joining surface area, has been used. Modern head gaskets are more often a combination of synthetic material with a metal core—often with enhanced metal rings that line the cylinder seal.
Marine engines often used what is called an "open" cooling system. Instead of using water or coolant from an enclosed onboard reservoir like a radiator, an open system draws from the water in which the boat is operating. While coolant or distilled water is not corrosive to internal parts, water used in open marine cooling applications probably is. Salt water is especially corrosive. Even if it's "fresh water", it may contain minerals, organic material or contaminates that cause rust or corrosion. While marine gaskets may use some of the same synthetic or composition gasket materials as automobiles and different anti-rust and anti-corrosive coatings, the primary difference is in the metal used. Both the base metal and the sealing rings for the cylinders are made from metals highly resistant to rust and corrosion, primarily bronze and stainless steel instead of the copper and steel used in auto applications.
- Photo Credit boat image by pearlguy from Fotolia.com
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