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  1. #1
    hitman's Avatar
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    zero compression means FAIL

    Kept fowling out the #1 spark plug and had loss of power. Had 0 compression on the #1 cylinder. Pulled the head to see what carnage lay beneath.











    Still not sure what caused it. Must have been something in the carb that caused it to lean out. I premix. Only had about 100 or so hours on a brand new SBT rebuilt engine. Had just rebuilt the carbs last year. Did not do needles and seats but I would imagine that would have caused a rich condition (not lean) if it was an issue.

    So now need to decide if I can get away with just a re-sleeve and an upper end rebuild? Anyone have any thoughts?


  2. #2
    Drag! def went lean , melted piston , snagged ring , smashed around , Looks like it may just have been top end and out the exhaust for debris? but since you have to pull the cyl you can look in the case and inspect the crank! , Thing is they are such a biatch to work on in the hull with the 3 cyl bank It would be easier to pull the motor IMHO and while it was out then I would open the case and make sure a seal didn't fail , but thats me ebay had some heads last time I looked

  3. #3
    Duke's Avatar
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    If I'm looking at the last picture right it appears the ring spun in the land, I can see what looks like the gap in the exhaust port. Most likely the locator pin came out and caused all the mayhem.

  4. #4
    hitman's Avatar
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    Quote Originally Posted by ZMANN View Post
    Drag! def went lean , melted piston , snagged ring , smashed around , Looks like it may just have been top end and out the exhaust for debris? but since you have to pull the cyl you can look in the case and inspect the crank! , Thing is they are such a biatch to work on in the hull with the 3 cyl bank It would be easier to pull the motor IMHO and while it was out then I would open the case and make sure a seal didn't fail , but thats me ebay had some heads last time I looked
    Pardon my ignorance, but what seal are you referring to? I am completely unfamiliar with the lower ends of these machines. I am mechanically inclined, just never tore into one.

  5. #5
    jdog800's Avatar
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    lots of times when u get alot of damage like that on the top of the piston its from the needle bearing under the piston comeing apart and the needles get sucked ontop of the piston and beat it up like that. Needle bearings comeing apart ususally points to bad lubrication either from lean condition or oil injection faliure.

  6. #6
    hitman's Avatar
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    Well it can't be oil injection failure becasue I blocked it off and went to pre-mix.

  7. #7
    jdog800's Avatar
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    Bad crank seal...leaky case...broken reeds sucked into oiler holes...anyone of those could make a lean condition. Have u checked the crank?

  8. #8
    hitman's Avatar
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    Judging by the look of the head and piston it doesn't seem like there was a lean condition. That head and piston are beat to hell. Seems like whatever caused it had to be steel. Couldn't it have just been a rod needle bearing that went out and got sucked in through the intake port?

    I will be checking the crank tonight.

  9. #9
    Quote Originally Posted by hitman View Post
    Judging by the look of the head and piston it doesn't seem like there was a lean condition. That head and piston are beat to hell. Seems like whatever caused it had to be steel. Couldn't it have just been a rod needle bearing that went out and got sucked in through the intake port?

    I will be checking the crank tonight.
    lets see the piston is completely black and has a low valley in the center where it was melting or is that just my monitor?

  10. #10
    jdog800's Avatar
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    when u get the piston out, turn it over and see if there is a dark spot under the piston crown

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