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    Chasing power loss

    I've been losing power in my 87 2550 ciera. Thought it was prop issue but started to get a lifter tick last season. Pulled intake today and all looked good until #2 intake lifter showed signs of abnormal wear. From a visual cam looks good. Lifter is still flat as well. Planning on replacing lifters n push rods and doing a break in. I'm thinking maybe other lifters may not be fully opening valves but not ticking due to being worn causing power loss. Any thoughts would be appreciated thanks in advance
    1987 bayliner 2550 5.7 omc cobra i/o

    #2
    It is possible that the camshaft itself is wearing out.

    I would reinstall the cam followers onto the same cam lobes.
    Remove all spark plugs.
    Start with #1 cylinder at TDC C/S.

    Position a dial indicator so that you can measure the up-lift of #1 intake and 1# exhaust cam followers.
    Bump the crankshaft over until you see the highest readings.
    Jot these down on paper.
    ​​​​​​​
    Now move to #8 cylinder at TDC C/S and do the same.
    Continue right down the firing order.

    If the cam profile is OK, these numbers will be very close to each other.
    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

    Comment


      #3
      On a flat tappet cam I think you have to replace the lifters & cam at the same time due to wear patterns. I might try reinstalling the lifters and adjust the lifters and then measure the amount of valve movement against specs. Valves that are too tight can lower compression.
      88 Four Winns 200 Horizon 4.3 OMC
      98 Jeep Grand Cherokee 4.0/Selectrac
      07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

      Long Island Sound Region

      Comment


        #4
        My first thought was to do a compression test both dry and wet...…..but you have already taken the engine apart so that baseline is unknown.

        I would still do a comp check once it is reassembled both dry and wet.

        If you have access to regulated air you could also do a cylinder leakdown test.

        Is it a 1987 engine?

        Ever rebuilt?

        Number of hours on it?
        Present Boat- 2018 VR5 4.5/200hp Mercruiser
        Last Boat- 1998 Capri 1950CL 3.0 Mercruiser

        Comment


          #5
          I've tried readjusting valves no change. My last compression test was around 120 to 130. No rebuilds known. Suspect original 1987. Hours unknown. From a visual cam looks good. All rockers look to move the same. From what I've researched can put new lifters if a break in is done. If cam goes out then it was going anyway. My main concern is I do see metal flakes in valley and top of heads on both sides.
          1987 bayliner 2550 5.7 omc cobra i/o

          Comment


            #6
            Originally posted by 6549vincent View Post
            I've tried readjusting valves no change. My last compression test was around 120 to 130. No rebuilds known. Suspect original 1987. Hours unknown. From a visual cam looks good. All rockers look to move the same. From what I've researched can put new lifters if a break in is done. If cam goes out then it was going anyway. My main concern is I do see metal flakes in valley and top of heads on both sides.
            That dial indicator check needs to also be compared against the lift specs for the cam.

            Each lobe may be worn a notable amount yet all will read almost the same for each lobe.

            Yes.......those metal flakes are evidence of wear.

            On a related note, I had a DOHC 4 valve engine (stock with regular oil changes all it's life) wipe One cam lobe into a perfect circle.

            Because the other exhaust valve still opened and closed, the car ran fine until the idle quality declined just enough to make it apparent if you looked at the coffee in a coffee cup in the cupholder, you could see the rhythmic motion of the liquid.

            The only reason I had it fixed was because the check engine light came on and would stay on.......so I could not pass my annual emissions check.

            The car still pulled strong from idle to redline and the only way you knew there was an issue was due to the light being on.

            I suspect your cam is worn and you will notice the peppiness when a new one is installed.
            Present Boat- 2018 VR5 4.5/200hp Mercruiser
            Last Boat- 1998 Capri 1950CL 3.0 Mercruiser

            Comment


              #7
              Your cylinder pressures of 120 to 130 psi are way too low for this engine.

              Hard to say what the metallic flakes are from at this point.
              Perhaps look at the valve stems, the tips of the valve stems, the rocker arm tips and the push rod sockets.


              And by the way, if a camshaft is going flat (worn and not providing the original lift), it will still operate the valves but only to the tune of what profile is left after having survived all of these years of service.
              As the lobes wear, the cam follower plunger begins to top out, hence the clicking that we may hear.
              In most cases this can be adjusted out by further tightening the rocker arm nut.
              The goal is to place the plunger close to within the center of it's travel.


              If you do put it back together, use the 8 stop cam follower adjustment procedure. If you are not familiar with that, post back and I'll walk you through it.


              Even as it sits (assuming that the cylinder heads are still in place), you will be able to do the leak-down test and learn if the issue is with the piston rings or with the valves, or with both.



              FYI..... we can safely install new cam followers (lifters) on a used flat tappet camshaft. The bottom of the followers offer the convex surface, not the cam lobes!
              However, without knowing if the camshaft profile is OK, this would be a waste of your time and money.


              .
              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

              Comment


                #8
                .........................
                Originally posted by vr5200 View Post

                That dial indicator check needs to also be compared against the lift specs for the cam.
                Ideally yes.
                However, if the OEM specs are not known, the intake lobe lift can be compared to all other intake lifts, and same with all of the exhaust cam lobes.
                Basically, you'd be comparing one against the other and so on. Not all will wear the same amount.


                Each lobe may be worn a notable amount yet all will read almost the same for each lobe.
                I would say that would be unlikely.


                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

                Comment


                  #9
                  Continued:

                  A few FYI's.

                  ..... Adding oil to a V engine's cylinder (as to find or eliminate piston rings as the issue), is ineffective.
                  Due to the cylinder not being vertical, the oil will tend to pool at the low side of the cylinder.
                  A false positive can be seen simply via the volume that the oil consumes. In other words, by adding oil to a cylinder, it can't help but to increase the cylinder's pressure simply by consuming combustion chamber volume.

                  .... Since camshaft operation and valve movement is measured in the thousandths on one inch, it is impossible to view any discrepancies by eye.
                  For this type of measurement, a precision measuring instrument is required.


                  .... Even with a tired engine, if the ignition timing is not dead on, and in particular the Progressive and Total Advance, no gasoline engine will perform at it's potential.



                  With regard to the OP's issue, it is very likely that cylinder heads need to be re-worked, and worst case, this engine is due for a complete over-haul.


                  .
                  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

                  Comment


                    #10
                    Can engine be pulled without removing outdrive?
                    if so how?
                    1987 bayliner 2550 5.7 omc cobra i/o

                    Comment


                      #11
                      I'd pull the drive, as long as its not really corroded on (driveshaft into coupler) its not a hard job at all. Should be done once a season anyway.
                      88 Four Winns 200 Horizon 4.3 OMC
                      98 Jeep Grand Cherokee 4.0/Selectrac
                      07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                      Long Island Sound Region

                      Comment


                        #12
                        Originally posted by 6549vincent View Post
                        Can engine be pulled without removing outdrive?
                        if so how?
                        If you have enough space in front of the engine (that would allow you to move it forward), you may be able to disengage the input shaft from the drive coupler.
                        If so, this would allow you to remove the engine while the drive is still attached.
                        However, going back in will be a different story.

                        Bottom line, you may as well pull the drive now.




                        FYI and FWIW......... If you are removing the engine for an over-haul, say no to these!




                        Ask your re-builder to use a better piston profile that can take advantage of the SBC cylinder head's quench surface. .



                        .
                        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

                        Comment


                          #13
                          Originally posted by 2850Bounty View Post
                          Your cylinder pressures of 120 to 130 psi are way too low for this engine.



                          .
                          what are good numbers?
                          1987 bayliner 2550 5.7 omc cobra i/o

                          Comment


                            #14
                            Originally posted by 6549vincent View Post

                            what are good numbers?
                            When each cylinder has been cycled through at least 3 compression strokes, we hope to see around 160 psi per cylinder, and with no more than a 10% difference between the high and low.
                            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

                            Comment


                              #15
                              Are these standard rotation motors?
                              I'm looking at an engine from s and j motors in Spokane wa. For 2200 shipped
                              1987 bayliner 2550 5.7 omc cobra i/o

                              Comment

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