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I did the 200 hour clean of the oil tank and then did the oil purge procedure on my 912ULS. I started the engine and let it warm up for a bit. Shut it off, worked quickly to remove the rocker covers, and checked to ensure that the lifters where inflated. In my haste, I pushed on the exhaust valve side of the rocker on cylinder #2. Of course, I moved the valve a slight amount. I realized my mistake and proceeded to work my way around to all the lifters. I reinstalled the rocker covers. When I tried to start the engine, it tried but would not start and shook a lot. It now looks like the exhaust valve on cylinder #2 will not close completely. No compression on #2. It seems like the lifter is over extended. Anyone seen anything like this?
  • Re: Exhaust value on cylinder won’t close completely

    by » 7 years ago


    As you found out the hard way; Hydraulic lifters have a spring in them and they will quickly enlarge to fill up any slack in the valve train.
    It's what they do! :whistle:

    The good news, maybe, is that they also adjust the other way very slowly.
    If kept under compression, they will leak oil back out very slowly.
    This is why you sometimes hear the lifters clatter for a few second after starting when the engine has not been run in a while.

    Rotate the engine so the problem lifter is in full compression with the problem valve fully open.
    Now, wait! It might take a few days to a week or more.
    If you are lucky the lifter will compress enough for the valve to close.

    I am not guaranteeing that this will work, but at least you don't have to disassemble the engine.
    It is worth a try.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


  • Re: Exhaust value on cylinder won’t close completely

    by » 7 years ago


    Thanks Bill. If I were to purge the system of oil to the point of getting air into the lifters I wonder if that would allow me to deflate the lifter quickly? Then I would go through the purge procedure to get the air back out of the system.

  • Re: Exhaust value on cylinder won’t close completely

    by » 7 years ago


    I don't think that will be necessary.

    In order to get Air into the lifter, you will need to get enough oil out of the lifter to make space for the air to get in.
    That would require the lifter to deflate under compression to the point that when the valve closes the lifter expands drawing in air.
    If the lifter is deflated enough to draw air, you might as well just let it refill with oil and then you will be back to where you were when you started.
    Don't make another problem for yourself.

    Patience is a virtue.

    I am going to change my original answer slightly.
    The lifter has a controlled bleed down that allows for it to shrink as the engine heats up and expands.
    This should permit your over-inflated lifter to return to normal in a few hours at most, instead of days.

    The problem may already be gone.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.


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