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Thread: Ummmmm what?

  1. #1
    Registered User zeiss150's Avatar
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    Dec 2003
    southern California

    Default Ummmmm what?

    So I just put together my P90 head (rocker, lash pads, cam) its off the car right now and I was setting the cold valve lash .010 exaust .008 intake. so thats all set, my question is why are hot valve settings bigger than cold. with the cam hot, the metal expands, making the cam closer to the rockers so then why would the gap be bigger than when they are cold set. shouldn't the hot setting be the smaller gap and the cold be the larger gap. What am I missing? I've hot set my Valves on my N42 several times so I know how to do it, but this is just bugging me.

    Thanks for the info, Matt

  2. #2
    Registered User
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    Dec 2006
    Kingston, ON


    I may be wrong, and Im sure someone will correct, but this is what i figure. The cam is not the only thing getting hot. Everything in there is getting hot including the aluminum head. Aluminum and steel undergo very different thermal expansions. Im pretty sure that aluminum expands more than steel. So your block get "thicker" making less valve stick up and giving you a larger gap.

    If I'm completely wrong, someone please correct me.

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