Sunday, November 3, 2013
Materials Used in Making Snowmobile Piston Rings
Snowmobile engines run the same way as engines in motorcycles. They have pistons that move up and down, compressing the air inside the cylinder and allowing detonation of gasoline inside the cylinder. Each piston has several rings with different purposes and often different materials.
The Basics
Pistons dont press against the walls of the cylinder -- this would cause too much friction. Each piston has three narrow metal rings around it that seal the combustion chamber from the oil in the crankcase below. In the past, rings have been made of cast iron, cast iron alloy, bronze, phosphor bronze, steel and stainless steel and can be chrome plated. Which metal is used depends on the nature of the engine.
The Materials which Make Up the Ring
Engines today use only steel, cast iron or enhanced cast iron for rings. Most snowmobiles come equipped with high-performance engines that use steel because of the demands on the engine. Iron rings can be used if they have been infused with graphite. These are called ductile iron rings. Cast iron rings are cheaper and a good choice for older snowmobiles.
The Reasons for Different Materials
Engines use three rings on each piston. The top ring has to handle the highest heat because it is closest to the combustion chamber. This ring must survive temperatures of 600 degrees Fahrenheit. Top rings are faced with a molybdenum coating. The top ring helps dissipate heat by conducting it from the combustion chamber to the rest of the engine. The second ring down the cylinder has to deal with temperatures of 300 degrees Fahrenheit and is made of steel for durability. The second ring has to do double-duty. It works with the top ring to seal the combustion process inside the cylinder and helps the bottom ring keep oil out of the combustion chamber. The second ring has a tapered edge that helps with oil control. The bottom ring specializes in spreading the right amount of oil around the cylinder walls. It often is made in three or more pieces with special twists.
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