Hydraulic Lifters & "Lifter Jacking" | FerrariChat
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Hydraulic Lifters & "Lifter Jacking"

Discussion in 'Technical Q&A' started by 4i2fly, Jan 17, 2005.

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  1. 4i2fly

    4i2fly Formula 3

    Apr 16, 2004
    1,333
    SF, Bay Area
    #1 4i2fly, Jan 17, 2005
    Can anyone point me to a technical book or a publication that can explain this concept in detail.Thanks in advance.
     
  2. ham308

    ham308 Formula Junior

    Nov 3, 2003
    358
    NE Switzerland
    Full Name:
    Richard Ham
    #2 ham308, Jan 17, 2005
    Do you mean hydraulic valve lash adjusters, - the things that take up the clearance in a valve drive?
     
  3. 4i2fly

    4i2fly Formula 3

    Apr 16, 2004
    1,333
    SF, Bay Area
    #3 4i2fly, Jan 17, 2005
    Apparently, engines with hydraulic lifters have fairly low exhaust back pressure limits. An increase in back pressure (excessive back pressure or clogged exhaust) will cause some degree of valve float. This valve float can cause the hydraulic lifter to re-set with the valve still open (not seated). This phenomenon is known as lifter jacking.

    What I am trying to find out is the technical details, drawings and consequences of this happening in an engine equipped with hydraulic lifters.

    Edit: It may be called something other than "Lefter Jacking"...
     
  4. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    36,756
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    #4 Rifledriver, Jan 17, 2005
    It was more commonly called "pump up". It was common on American high performance motors up until the early 70's or so when most of the performance valve train builders solved it. I really have not heard of it since then except when I was involved in some discussions trying to figure out why 355s were having such a problem burning valves. A couple of us theorized that could be a contributory factor as 355s are the first Ferrari with hydraulic valves. They were also the first Ferrari that had a problem with burning valves. Ferrari poo-pooed the idea with out even considering it. Thomas McKeller at Ferrari Atlanta was also one of the people that thought it a possibility.

    I would think if you got in touch with Crane, Isky or someone like that you could get some answers to your questions. Call Elgin cams, they are in your neighborhood and talk to them.
     
  5. ferrarifixer

    ferrarifixer F1 Veteran
    BANNED

    Jul 22, 2003
    8,520
    Melbourne
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    Phil Hughes
    #5 ferrarifixer, Jan 17, 2005
    My belief is that it is a valid thoretical problem, but I just can't see the back pressure being anything like enough to slow down valve closure enough to allow the lifters to expand.

    Lifter expansion is a relatively slow process too, so the time it has to expand is minimal.

    Also, I've not seen any evidence of it in any of the 360C engines I've built, or the 550, but that doesn'y mean it's not happening.
     
  6. ham308

    ham308 Formula Junior

    Nov 3, 2003
    358
    NE Switzerland
    Full Name:
    Richard Ham
    #6 ham308, Jan 17, 2005
    Here's some information
    http://www.delphi.com/pdf/e/valve_hla_12mm.pdf

    Pumping up occurs when positive contact force is lost in the valve drive at high engine speeds (should be well above the rated speed). In my experience it has got to be a considerable loss of contact though. A bit of valve bounce should not cause problems. For example on a system where the measured contact force between the rocker and valve goes down to zero for quite a bit of the opening event we had no problems. Hope this helps
     

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