How Does Lycoming Valve Seats Get Oil?

Discussion in 'Firewall Forward / Props / Fuel system' started by HomeBuilt101, Jan 25, 2020.

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  1. Jan 25, 2020 #1

    HomeBuilt101

    HomeBuilt101

    HomeBuilt101

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    Looking at the engine parts manual I am trying to figure out how the valve train gets oiled on the Lycoming...

    Is appears that the lifters have an oil hole that pushes oil into the pushrod and since the pushrod shafts are hollow the oil gets forced through the pushrod up (out) to the rocker arm and this oil flow gets pushed through the rocker arm and the rocker arm shaft has a hole that channels the oil to the rocker arm bushings and I guess the tip of the rocker arm has a hole that channels oil to the valve tip...IS THIS ACCURATE???

    If the above is true then how does the valve stem itself get oiled?

    THANKS for the help!!!
     
  2. Jan 25, 2020 #2

    akwrencher

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    I am not intimate with Lycomings, been a while since I had one apart. But, to answer part of your question, engines typically do not have dedicated oiling to valve stems. There is enough oil most floating around in the air to do the job. I suspect this is the case for Lycomings as well. In fact, any engine with valve stem seals does not have any oil lubricating the valve stems.

    I should add as well, the title of the thread is about valve seats, which also do not get oiled. They would carbon up and the valve would overheat and burn. Valves need good clean contact with the seat to help with cooling. At least, that's my understanding
     
  3. Jan 25, 2020 #3

    Dan Thomas

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    You have it right. A bit of that oil seeps down the valve stem, too, but too much just carbons it up real bad and makes it stick. Valves, at least in old-design engines, are lubricated by the tetraethyl lead in the fuel, though more modern Lycs and Conts have been using valves, seats and guides that can run with no lube. Some valves have stem seals on them to keep the oil out of there, same as your car's engine. Furthermore, turbocharged engines have pressure in both the intake and exhaust and that alone would keep the oil out.

    Remember that there is very little radial load on a valve stem. The lube is most needed between the end of the stem and the rocker, since there's a sliding motion there on an area under quite a bit of pressure. That rocker moves in an arc, while the stem moves in a straight line. If that rocker/stem interface isn't well lubed, the stem starts wallowing out the valve guide.
     
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  4. Jan 25, 2020 #4

    HomeBuilt101

    HomeBuilt101

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    >I should add as well, the title of the thread is about valve seats, which also do not get oiled.

    Yup...my bad...After I hit the old post button I had a Homer Simpson moment...

    !!!DOH!!!

    THANKS for the clarification!!!
     
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  5. Jan 26, 2020 #5

    BBerson

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    You (OP) have some time to edit the title yourself (not sure, maybe 24 hrs?)
    Use tools upper left of screen.
     
  6. Jan 27, 2020 #6

    pfarber

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    Most valve guides are brass or cast iron alloy, both metals with decent 'self lubricating' ability. The valve stems being extremely hard and polished also helps reduce friction. A tiny amount of oil makes its way to the valve guide, but unless the guide clearance is excessive, it never makes it to the valve head.
     
  7. Jan 27, 2020 #7

    Dan Thomas

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    Bronze, never brass. Brass wears real fast. I worked in an industry where a startup aftermarket bearing manufacturer didn't know the difference and sold a lot of bearings that lunched the machinery.

    Lycoming and Continental used bronze valve guides for a long time. In 1999 Lyc switched to a high-chromium-content bronze, as they were having wear issues especially in the larger engines. The wear problems went away. There are dozens of bronze alloys for different aplications. I once solved a wear problem by switching from C93200 to an aluminum-bronze, and it worked but that allow was miserably tough to machine. Not something you'd expect from adding soft aluminum to bronze.

    Iron works OK in liquid-cooled engines, especially in iron heads, but an aircooled aluminum head expands at twice the rate of the iron and the guide will come loose. Bronze has the same coefficient of linear thermal expansion as aluminum and will stay put.
     

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