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On 13 Jul 2002, at 23:04, Carver wrote: > AVP oversizes the seat, chills it, and installs it in an undersized head > opening. Staking only has a local effect, and they tried it and changed. > Maybe they do a all-around staking, too, I forget. My '80 Vanagon dropped > it's valve seat. Theirs don't drop. They specialize in T4 engines. I worry about just increasing the interference (that's the term for the amount of mismatch between the sizes) in this kind of application. The aluminum around the seat will be under tension from the press fit, and this tension can lead to the head cracking. Of course, if the the head cracks, the interference becomes pointless. Finding a good valve seat material that matched the thermal expansion properties of aluminum would be a perfect solution. Brass or bronze is a step in the right direction, which is why I asked about this, but I think only Keith responded that he didn't know anything about this. The real question about bronze is whether it can take the punishment of a valve seat. The coefficient of expansions of these 3 materials are: steel: ~6.6 alum: 13 brass/bronze: 9.8 - Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/