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  1. #1

    Default Mercruiser 7.4 Horizon a tick to a knock

    1998 7.4 Horizon 380hp in a Sea Ray started to tick then developed into a bit of a knock, the factory oil pressure gauge went from 60 at WOT to less than 40. Here is a video to add some sound to the issue.

    https://youtu.be/MvCVlyiXuCs

  2. #2
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    4,232

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    loose rocker arm, bent pushrod, pulled rocker stud, stuck/bent valve

  3. #3
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    2,837

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Engine life @ WOT measured in 10s of hours...to very low hundreds at best...
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

  4. #4

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Quote Originally Posted by Bt Doctur View Post
    loose rocker arm, bent pushrod, pulled rocker stud, stuck/bent valve
    Ok, so I removed the intake manifold, rocker covers, and the lifter guide hold-down plate. All of the lifters move freely, and don’t appear to be scored. The rockers don’t feel too loose in there TDC position. The cam lobes that I can see aren’t scored. The pushrods don’t appear to be bent. So next step remove the rockers and pushrods, roll the pushrods across the table and see if one has a slight bend?

  5. #5
    Join Date
    Dec 2006
    Location
    Chaumont Bay, N.y., USA
    Posts
    5,505

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    started to tick then developed into a bit of a knock, the factory oil pressure gauge went from 60 at WOT to less than 40.

    So next step remove the
    Ayuh,..... Next step is to pull the motor, 'n strip it down,....

    Sounds more like yer gonna be rebuildin' the bottom end,....
    Any Grease is Better,... Than No grease at All....

  6. #6

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Engines aren't my strong suit, so I'm asking more than suggesting. Are the lifters hyd. to take up slack? If so, could one be bad?

  7. #7

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Quote Originally Posted by bondo View Post
    Ayuh,..... Next step is to pull the motor, 'n strip it down,....

    Sounds more like yer gonna be rebuildin' the bottom end,....
    With all of the videos I’ve been watching it is starting to sound more like maybe a rod bearing has spun than a valvetrain issue. I was just hoping it wasn’t something like that.

  8. #8

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Quote Originally Posted by harringtondav View Post
    Engines aren't my strong suit, so I'm asking more than suggesting. Are the lifters hyd. to take up slack? If so, could one be bad?
    Yeah, they are hyd. roller lifters. A collapsed one could make a noise like this. But, I think usually you would have a really loose rocker on one of the valves that would indicate something like this was happening. Unless I’m missing something, I’m not seeing anything wrong with the valvetrain yet, which sucks. I will keep investigating after I get off shift though.

  9. #9

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    Quote Originally Posted by Harborite88 View Post
    Yeah, they are hyd. roller lifters. A collapsed one could make a noise like this. But, I think usually you would have a really loose rocker on one of the valves that would indicate something like this was happening. Unless I’m missing something, I’m not seeing anything wrong with the valvetrain yet, which sucks. I will keep investigating after I get off shift though.
    Not trying to play out of my league here, but the noise didn't sound like a deep crank or connecting rod knock. But I wasn't there. Think about what causes a drop in oil pressure. Unfortunately that includes a loose con rod. Any where else an oil gallery feed might have little too much clearance?

  10. #10
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    4,232

    Default Re: Mercruiser 7.4 Horizon a tick to a knock

    The rockers don’t feel too loose in there TDC position

    They should not be looses in any position

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