60-67 Buying Diesel 7/15/14 11:37 AM Page 64
Diesel Pistons
for different engine applications.
Steel Pistons Big over-the-road heavy-duty truck engines are expected to last a lot of miles, upwards of a million or more with proper maintenance and care. Cast aluminum pistons hold up well enough in light to moderate use applications, but for high output engines, two-piece "articulated" pistons with steel crowns and aluminum skirts may be used for improved durability. The wrist pin holds the two pieces together, and allows the piston to handle higher loads than would be possible with a one-piece cast piston. One-piece steel pistons have also been around for a number of years and offer numerous advantages over cast aluminum, forged aluminum and twopiece aluminum/steel pistons in hard working diesel engines. Steel pistons are more expensive to manufacture than cast or forged aluminum pistons, but steel is much stronger than aluminum and can handle higher loads and temperatures without failing. Weight would seem to be a disadvantage, since steel is a heavier and denser metal than aluminum. Yet steel pistons can be as light or even lighter than
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aluminum pistons, if mass is removed in areas where extra strength isn't needed. Ring land wear is also not a problem with steel pistons because the entire piston is steel. Another advantage with steel is that its coefficient of
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