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Yamaha 150 2 Stroke Water in Cylinder

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  • Yamaha 150 2 Stroke Water in Cylinder

    Yamaha 2002 OX66 150hp. Always been a salt water engine. Low hours.
    Motor sat for 5 months while I was up north.
    Wouldn't turn over when I got back, found the lower port piston stuck, rusted.
    Freed it up, got the motor running, idles rough, hammering sound, but runable.
    All cylinders 120 expect lower port cylinder 90.
    Replaced head and gasket but did not look like the head gasket was blown.
    Same thing, lower cylinder 90 (I suspect stuck ring from when it was frozen), runable.
    Water shows in lower plug and light brown watery residue shows in the plug above.
    Plugs look steam cleaned no oil or carbon.
    O2 sensor that was new since the head gasket job was 50 percent plugged with dry rusty residue.
    Pulled head again, gasket looks ok. Foamy crud in two cylinders, see picture.
    I am suspecting cracked block or somehow water getting into exhaust system.
    Any ideas on verifying what is going on would be appreciated.
    Attached Files

  • #2
    I’d guess that your oil feed tank in the bilge might have got some water in it ? Just a thought.


    • #3
      Pulled the exhaust cover and found a hole in the block (see image)
      Water has been entering exhaust chamber here and entering the two lower cylinders.
      Going to have it welded and hopefully will be good to go.

      Attached Files


      • #4
        When you find rusted spark plugs, it's a clear indication that some sort of water intrusion is going on inside exhaut chamber making its way into the combustion chamber area. This area is usually bypassed and head gasket is blamed for...

        Happy Boating

        Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers


        • #5
          Usually welding will open up other holes do to heat....Its eroded from the inside outward and the aluminum is thin.Best to replace it...
          When in doubt,Trim it out!!!
          Business Owner & Certifed Technician
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          • #6
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            Fatzbullet is right. Welding not practical due to the additional corrosion that is no doubt hiding behind the hole. You would probably just blast out a bigger hole. Two local welding places would not touch it unless the block is out of the boat.

            Replacing the powerhead is not an option for considering the cost and the risk you take of getting a poor rebuild.

            I put an ALUMINUM screw through the hole to act as a filler (and a clean surface for the epoxy to grab) and applied JB Weld High Temp epoxy putty to both sides.
            Time will tell.