oil stained intake runners?

Discussion in 'Oil and Lube Systems' started by Grumpy, Oct 25, 2017.

  1. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

    this is not at all rare, especially on newer engines that have mild performance cams.
    in most cases the cause is a small amount of oil leaking past the rings or valve seals, especially if the heads you installed were not equipped with new valve seals.
    theres a good chance reversion pulses are causing a fine oil mist, from oil getting past the valve seals, valve guides or rings, during the cams low speed operation (idle) too be sucked back into the intake plenum
    keep in mind REVERSION PULSES in the intake can spread oil over the runner and plenum in some cases.
    many guys see this if they install older heads , on an engine that are basically in good shape but may have minor wear on the valve guides and valve seals, or before the piston rings fully seat and seal.on a new short block , especially , if the engines PCV valve and breather are not functioning at peak efficiency.
    often installing a breather catch can significantly reduces this, but if your cars engine "LOPES" and "RUMBLES" at idle one of the strong indications that the engine sees some intake charge reversion, at low speeds , its almost a given that their will be minor reversion, and as a result minor oil film on the intake runners.
    if youve ever installed a longer duration cam in a tuned port engine design, your very likely to find the intake runners show a light oil discoloration as the engines allowing those long runners to draw oil up out of the cylinders at lower idle speeds during the cams over lap timing.
    you might want to pull a spark plug and use a flex micro cam to inspect inside the cylinder



    this is also a good inspection tool
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    heres a cheaper version that works with a lap top computer

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    a common cause of oil in intake ports is having the heads machined without matched changes to the intake, manifold, and gasket surfaces, but reversion pulses in the intake runners can and do transfer oil from the valve guides and oil mist,getting past piston rings into the intake runners due to reversion pulses


    read through these links






    Last edited: Feb 20, 2018

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