Valve Seat Selection and Machining
Valve Seat Selection and Machining
When rebuilding a cylinder head for a stock automotive application, a performance engine, or a heavy-duty diesel, what kind of replacement seats should you use if the original valve seats need to be replaced? Should you install new seats that are the same as the original seats, or should you use a different type of seat material or alloy that provides better valve cooling or wear resistance?
The type of seat material that’s “best” for a particular cylinder head will depend on the application, the type of fuel used, how much power the engine produces, the type of valves (stainless steel or titanium), and what kind of longevity and durability the engine is expected to deliver.
A hard, wear-resistant valve seat is obviously a must for any engine application that will see a lot of miles. Stock passenger car and light truck engines as well as performance street engines need seats that are wear resistant so they will last. Heavy-duty diesel engines are even more demanding, and require seats that can go hundreds of thousands of miles. So cutting corners by installing the cheapest cast iron low alloy seats you can find is probably not the smartest move on such applications.
One valve seat supplier we interviewed said cost seems to be overriding almost every other consideration these days because of the current economic crunch. “The market has been flooded with cheap valve seats from China, India and Korea. Consequently, the average selling price of a
cast iron valve seat today is about half what it used to be. The low prices may seem like a bargain for engine builders, but the quality of these cheap imported seats is all over the place. People who used to buy high quality made in USA alloy seats for $5 are now buying $2 cast iron seats from overseas – and are learning the hard way that many of these seats are no bargain at all.”
If an engine comes factory- equipped with heat-resistant nickel or other alloy valve seats,
substituting plain cast iron valve seats to save money is asking for trouble. Plain cast iron seats won’t hold up with unleaded gas in a late model, highly stressed engine.
Another trend that valve seat suppliers are seeing today are engine builders replacing valve seats more on a piecemeal basis than replacing an entire set. “We’re getting more calls for one or two seats instead of a complete set. We’re also getting more requests for replacement valve seats by size rather than by part number or application.”
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