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Low compression #2&4

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by gtfireftr, Oct 9, 2020.

  1. gtfireftr

    gtfireftr Member

    285
    Oct 9, 2014
    Westport MA
    1997 Sea Ray Sundancer 290
    Twin 4.3 liter w/Alpha Drives
    1998 290 DA, twin 4.3's..... Changed engines in 2017, both have about 100hrs since... I felt I had an issue, but I thought the bottom may have been dirty from not using very much in the past few weeks..... Went to start port motor and she would not fire... I figured flooded.... Went back the next day with a set of plugs and my compression gauge....... results are as follows...
    #1 150, #3 148, #5 150
    #2 90, #4 30, #6 150.....
    I am hoping I have a blown head gasket...... Any direction is appreciated.....

    TIA
     
  2. mike15

    mike15 New Member

    9
    Mar 30, 2015
    Lake Erie
    300 Sundancer 2005
    5.0 Mercruiser w/Bravo III Drives
    Do a leak down test, tuliped valves would be my guess.
    I had a similar issue this spring and it was the valves. If the you lug the engine it will build cylinder temperature and the valves will pull up into the seats and lose compression. I was shocked when it happened to me because I don’t hot rod my boat. But I think my boat was over propped for the load of stuff on our boat.
     
  3. gtfireftr

    gtfireftr Member

    285
    Oct 9, 2014
    Westport MA
    1997 Sea Ray Sundancer 290
    Twin 4.3 liter w/Alpha Drives

    Thanks for your reply..... I am just trying to figure out why it would be 2 cyl's adjacent to each other....Well if it's not head gasket I guess the next best would be that.....
     
  4. Strecker25

    Strecker25 Well-Known Member SILVER Sponsor

    Nov 20, 2014
    Rochester, NY
    2002 410DA
    Caterpillar 350HP 3126
    I'd pull the head and get a look at it. I had something similar when our motor went but I ran it for a few extra minutes and it burned a nice hole in the block between the two cylinders, forcing a full rebuild.
     
  5. joeyleggz

    joeyleggz Active Member

    650
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    Are you raw water or fresh water cooled ?Did you check your oil did the level increase? Are you losing any antifreeze? How were the plugs when you pulled them out? Were they wet with gas, oil, antifreeze/water This is usually tell tale signs with a blown head gasket
     
  6. gtfireftr

    gtfireftr Member

    285
    Oct 9, 2014
    Westport MA
    1997 Sea Ray Sundancer 290
    Twin 4.3 liter w/Alpha Drives
    Raw water cooled....oil level is good, no increase...... plugs were wet....
     
  7. NorCal Boater

    NorCal Boater Well-Known Member SILVER Sponsor

    Jan 24, 2008
    Covington, LA
    Boatless
    No boat....no engines
    I would be stunned if its not a head gasket. But that begs the question....why? On a motor with only 100 hours.
     
  8. gtfireftr

    gtfireftr Member

    285
    Oct 9, 2014
    Westport MA
    1997 Sea Ray Sundancer 290
    Twin 4.3 liter w/Alpha Drives
    I agree..... crazy stuff....
     
  9. NorCal Boater

    NorCal Boater Well-Known Member SILVER Sponsor

    Jan 24, 2008
    Covington, LA
    Boatless
    No boat....no engines
    With wet plugs I might look at the exhaust flapper valves. If raw water were able to get in the cylinder it would increase compression. That additional compression would have to go somewhere and the head gasket would be the line of least resistance.
     
  10. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    So did you get the heads off yet?
     
  11. gtfireftr

    gtfireftr Member

    285
    Oct 9, 2014
    Westport MA
    1997 Sea Ray Sundancer 290
    Twin 4.3 liter w/Alpha Drives
    I am probably gonna wait for spring.... I dont want to leave it apart over the winter......
     
  12. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Well how are you going to be certain there isn't water sitting on bare metal parts?
     
  13. NorCal Boater

    NorCal Boater Well-Known Member SILVER Sponsor

    Jan 24, 2008
    Covington, LA
    Boatless
    No boat....no engines
    What Scoflaw said....do not let it sit until spring. If there is water where it’s not supposed to be you’re giving it 5-6 months to make things worse.
     
  14. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I see he's on another site inquiring about a swap to V8's, which sounds like a good idea for that size boat.
     
    Strecker25 likes this.

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