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Engine not achieivng proper RPMs issue resloved 5.7 1988 Cobra 2556-gctid815817

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    Engine not achieivng proper RPMs issue resloved 5.7 1988 Cobra 2556-gctid815817

    Thought I would post this for someone else. I rebuilt the top end of my 5.7 1988 Cobra last year after taking on water from bad manifolds and risers. The mechanic who did this with me has sadly since passed away. Since the install I have not been able to get the engine to run past 2500 rpms. Finally figured out the valves were too tight. A mechanic friend explained if the valves are over torqued the engine does not get enough air and therefore wont pull enough fuel. I readjusted them by backing off each rocker until you hear them tapping at low idle. Once the tapping stops add a 1/4 turn. Once I adjusted all of the valves and now she ran up past 4000 on a full load in a choppy sea. This has been dogging me since last year and I lost a season because of it. Thought I would post this in case anyone else has a similar issue. This is a great forum and a great place to share issues and get support to help keep these old boats running! Thanks everyone...

    #2
    One and only time a new or rebuilt I installed or help install came from Michigan motorz valves too tight, took a very long week to figure out.

    For the record I still recommend them.

    The guy who's boat it was would not allow a start on a crate and no compression test, ether one I would have caught it, only time I didn't do ether.
    Be good, be happy, for tomorrow is promised to no man !

    1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

    '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

    Manalapan N.J

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      #3
      "jrr4948" post=815817 wrote:
      ......... Since the install I have not been able to get the engine to run past 2500 rpm.

      1...... Finally figured out the valves were too tight.

      2...... A mechanic friend explained if the valves are over torqued the engine does not get enough air and therefore wont pull enough fuel.

      3..... I readjusted them by backing off each rocker until you hear them tapping at low idle. Once the tapping stops add a 1/4 turn.

      Once I adjusted all of the valves and now she ran up past 4000 on a full load in a choppy sea.

      4...... This has been dogging me since last year and I lost a season because of it.
      [color]blue wrote:


      First...... I am sorry to hear that your mechanic friend has passed away.

      1..... just a friendly FYI. We do not actually adjust valves per 'se. What actually occured was that your rocker arm adjusting nut had been turned "IN" too far, thus setting the cam follower plunger too deep! This is what prevented your valves from fully seating at the higher RPM range.

      2..... Partially correct! And again.... there is no torquing or adjustment of valves!

      The issue was that these cam followers were preventing the valves from fully seat during both the compression and combustion cycles.

      3..... Yes, this is refered to as a dynamic cam follower adjustment.

      By doing this you first found zero rocker-arm-to-valve-stem lash.

      After zero lash, the additional 1/4 turn further "in" set the cam follower's plunger depth.

      4..... Unfortunately, running this engine last season may have damaged some valves and/or valve seats.

      You may want to perform a cylinder leak-down test and a cylinder pressure test!

      **************************************************

      For those of you reading this and/or who may be re-installing fresh cylinder heads, or installing a new or re-man'd SBC Engine, the 8 stop static cam follower adjustment procedure is what you should be using.

      If you need help with this, please ask.

      .[/color]
      Rick E. Gresham, Oregon
      2850 Bounty Sedan Flybridge model
      Twin 280 HP 5.7's w/ Closed Cooling
      Volvo Penta DuoProp Drives
      Kohler 4 CZ Gen Set

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        #4
        Always an education here! Thank you for the detailed explanation - much appreciated. JR

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