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  1. #1
    Join Date
    Aug 2011
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    Falmouth
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    Question Compression Test Anomaly ?

    Have had separate yacht and specific engine surveys done on a potential new to me boat. Engine is a VP 2003 (and yes the DB Marine hex mod has been done ), Engineer says that the compression test shows 230 psi on cylinder 1 and 270 psi on cylinders 2 and 3. That seems quite a large difference. to me and I’m awaiting a more detailed report. In the meantime... Thoughts?
    "Just because nobody complains doesn't mean all parachutes are perfect."

  2. #2
    Join Date
    May 2001
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    North Wales, sailing Aegean Sea or Menai Strait
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    21,903

    Default Re: Compression Test Anomaly ?

    Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.
    Answers to some technical queries at new website http://coxeng.co.uk

  3. #3
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    Aug 2011
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    Falmouth
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    2,345

    Default Re: Compression Test Anomaly ?

    Quote Originally Posted by vyv_cox View Post
    Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.
    I cannot confirm that but the engineer is a well respected and much recommended chap (including by the yacht surveyor) so I think I can trust he knows what he was doing. I’m waiting for the full report.
    "Just because nobody complains doesn't mean all parachutes are perfect."

  4. #4
    Join Date
    Jan 2011
    Location
    Shropshire/Empuriabrava
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    2,857

    Default Re: Compression Test Anomaly ?

    Quote Originally Posted by vyv_cox View Post
    Can be quite minor problem such as valve not seating properly to piston rings gone. Was a test done with oil in the bores? That will give a good clue.
    +1

  5. #5
    Join Date
    Nov 2009
    Location
    Home UK Midlands / Boat Croatia
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    19,805

    Default Re: Compression Test Anomaly ?

    Quote Originally Posted by colind3782 View Post
    +1
    I believe that the recommended difference between best and worst is normally supposed to be 10% .... but, in my experience, it is not that unusual for older engines to have 20% or more difference and still run perfectly well. If the engine starts well, runs well, doesn't use excessive oil and doesn't smoke other than on initial start-up, then I wouldn't worry about it. However, you could justifiably use it as a negotiating tool.

    Richard

  6. #6
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Richards Bay East Coast Africa
    Posts
    7,030

    Default Re: Compression Test Anomaly ?

    Quote Originally Posted by KevO View Post
    Have had separate yacht and specific engine surveys done on a potential new to me boat. Engine is a VP 2003 (and yes the DB Marine hex mod has been done ), Engineer says that the compression test shows 230 psi on cylinder 1 and 270 psi on cylinders 2 and 3. That seems quite a large difference. to me and I’m awaiting a more detailed report. In the meantime... Thoughts?
    A cylinder leakage test can help indicate where the problem is (valves , rings, gasket,etc)
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/yclt6l68

  7. #7
    Join Date
    May 2018
    Posts
    724

    Default Re: Compression Test Anomaly ?

    Quote Originally Posted by Rogershaw View Post
    A cylinder leakage test can help indicate where the problem is (valves , rings, gasket,etc)
    +1

  8. #8
    Join Date
    Feb 2010
    Location
    Glasson Dock
    Posts
    2,784

    Default Re: Compression Test Anomaly ?

    If the engine was cold when the first compression test was done there could have been less compression as there would be less oil in the cylinders.
    Then when the second cylinder was tested there would have been more oil in the cylinder bores thus more compression etc.
    (perhaps I am clutching at straws to think of a solution)
    Perhaps if you had another compression test starting at the furthest cylinder you could find that the last cylinder (being 130psi) may be higher.
    Certainly the difference is too large to ignore.

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