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  1. #1
    Hydrotherapy's Avatar
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    advice on piston crown pitting

    i have just pulled the head off jump boat as the last time i was out she kept stalling when hot,but always started straight away on the button.
    anyhow thought best to pop the head off for a look incase it was something else,on closer inspection all three bores are great but the wash looks a little rich as expected as i left it fat and two out on the highs but she peaked at 1 1/2 but this is a fun boat so i thought better safe than sorry...
    has anyone come across this pitting before and if so what was your findings,
    its #3 which is pitted,should i forget it,replace the piston,ect..
    no history of any failure on this boats engine what so ever and still runs strong....
    thanks in advance and looking forward to hear what you guys say
    added..
    vf11's,carbed 1300,advent,running 1200 ignition,150 psi across,riva f/a's
    edit.just cleaned the dome on #3 after taking a few pics and there is a tiny tiny ammount of pitting around the squish band area..tiny ammount not like piston crown
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	pitted piston crown on jump boat 001.JPG 
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Name:	pitted piston crown on jump boat 002.JPG 
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    Last edited by Hydrotherapy; 06-03-2009 at 05:29 PM. Reason: further info


  2. #2
    Hydrotherapy's Avatar
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    head pics
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  3. #3
    Hydrotoys's Avatar
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  4. #4
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    Looks like at one time something was hitting it.

  5. #5
    Hydrotherapy's Avatar
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    Quote Originally Posted by JIM'S PERFORMANCE View Post
    Looks like at one time something was hitting it.
    the dents in the head are tiny,nothing like the crown,i assumed if an object was in there they would be uniform in size on the dents,its as if the head is hardly touched..

    guys are there any engine internals i can afford to loose out the exhaust port without having to worry..

  6. #6
    Moderator DrewNJ's Avatar
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    for some reason that just looks a lot like deto to me...very minor though..
    Crappy gas maybe?

  7. #7
    Moderator RX951's Avatar
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    those look like signs of detonation to me.

    read this thread
    http://greenhulk.net/forums/showthre...ght=detonation


    if it were a piece of metal, it would hit surfaces all over the head in a sporadic pattern in different depths. This is looskliek signs of abnormal combustion.

    Has anything changed?

    • timing
    • premix ratio
    • octane
    • compression
    • gas selection
    • advent settings

  8. #8
    steach's Avatar
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    Quote Originally Posted by DrewNJ View Post
    for some reason that just looks a lot like deto to me...very minor though..
    Crappy gas maybe?
    +1 but more like cavitation???

    Is a small amount on water vaporizing in the squish area?

  9. #9
    One day at a time..... N8R's Avatar
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    Quote Originally Posted by DrewNJ View Post
    for some reason that just looks a lot like deto to me...very minor though..
    Crappy gas maybe?
    I was thinking deto to but, if this is the jump boat and if the ski is low on fuel then the constant fuel pump not getting fuel??????????????

  10. #10
    Moderator RX951's Avatar
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    remember, as temperature increases from [engine cooling or fuel mixture], so does your chances of deto
    Also, extra back presussure can increase deto.
    Too lean of a mixture can also increase deto. temps run up, chances increase.

    http://greenhulk.net/forums/showthre...ght=detonation

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