Opinion on Compression

Discussion in 'Mechanic Recommendation Forum' started by Graham Ridley, May 7, 2017.

  1. Graham Ridley

    Graham Ridley New Member

    Nov 8, 2016
    Ottawa canada
    260 Sea Ray Sundancer
    I have a 1985 Sea Ray 260 it has a 5.7 liter engine. I have just run a compression test and have the following results:
    1) 142 209
    2) 126 205
    3) 180 224
    4) 185 215
    5) 125 170
    6) 105 160
    7) 185 208
    8) 120 180

    Should I be concerned or replace the rings? Suggestions and opinions welcome.
  2. scoflaw

    scoflaw Active Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I'd be concerned. How's it run ? How much oil does it use ? Can you live with it ? I'd pull that out in a heart beat if it was mine, but that's me.
  3. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    We see this a lot on the Gulf coast where boats have been stored over the winter. When not running, several intake and exhaust valves are open and sometimes surface rust forms on the valve face. Before I did anything or spent any money, I'd run the boat for several hours at a decent or planing speed and then retest the compression. You might be lucky and find that the valves clean up and the problem will go away.
  4. Air O'Nautical

    Air O'Nautical Active Member

    Feb 5, 2008
    Stamford CT "Ponus Yacht Club"
    1995 400EC. Raymarine E80,4kw dome, Garmin 235 gps, 11ft Baltik / 15hp on St croix davits.
    2013 7.4L Mercruiser Blue water.
    Hurth straight shaft 630's,
    Westerbeke 7.0 BCG
    From experience, I completely agree with Frank.
    Those numbers are currently not acceptable!

    Boats that aren't run often, are subject to rusty valves that affect sealing and therefore compression. This is why we here in the North fog our GAS engines with oil during winter lay-up (Diesel engines are already full of oil).
    It's rarely the bottom of the engine that's the problem, piston/rings ect.
    A top end job is a common procedure.
  5. scoflaw

    scoflaw Active Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    The wet test has been used as a benchmark to check ring condition. It would be unreasonable to think the oil came up off the piston and sealed both intake and exhaust valves to the degree that was observed in his wet/ dry results.

    Totally agree with running it and retesting. Leak down test would give more insight to where the lost compression is going
  6. Bt Doctur

    Bt Doctur Active Member

    Aug 21, 2010
    New Jersey
    Ex SRV 240 Weekender twin
    in between
    Those reading are do not correspond to a 32 year old engine. see post 4

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