On fuel & valve seats...
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  1. #1
    Moderator Alan S's Avatar
    Join Date
    Mar 2001
    Queensland, Australia

    On fuel & valve seats...

    A while back a string ran regarding valve seat recession and unleaded fuels etc.
    At the time I made mention of the conditions & recommendations by Briggs & Stratton on their larger motors & this was questioned. I've come across the B & S handbook & this is what it says:


    This engine will operate on any gasoline intended for automotive use. A minimum of 77 octane is recommended.........
    We recommend the use of clean, fresh, lead-free gasoline.............................Leaded gasoline may be used if lead free is not available. Use of lead-free gasoline results in fewer combustion deposits and longer valve life.

    There seems to be something contradictory to what we've been led to believe including low octane & unleaded fuel; anybody got any theories?

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  2. #2
    Fellow Frogger! AlsPug504's Avatar
    Join Date
    Jul 2002
    You could premium 103 to sort the octane no problem. There is a chemical use in gasoline called MMT that is suppose to retard recession of the seat by stopping the valve from sticking to the seat. (According to mobil)

  3. #3
    1000+ Posts Pugnut403's Avatar
    Join Date
    Mar 2003
    I think you will find that the Briggs and Stratton motors have a lower compression ratio than most modern car engines. This would enable them to use lower octane fuel.
    Also the fact that they are mostly sidevalves would help too, as the shape of a sidevalve combustion chamber usually gives a slower burn which helps with low octane.
    The Briggs and Stratton motors are made of Aluminium, so they have to have hardened valve seats, and unleaded has been available in the US for many years now.
    Also, valve seat recession does not usually occur at lower revs anyway, and stationary engines do not usually run that fast.
    Pugs Rule!

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