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1999 Yamaha 0X66 powerhead blown help

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  • 1999 Yamaha 0X66 powerhead blown help

    This is a 200hp engine. Took it to a shop and they gave me the bad news. #5 piston they said is in pieces yikes. It also blew a hole in the cylinder wall. They said also #6 piston only had 30lbs of pressure. The rest were fine. He suspected the problem was a high pressure fuel pump because of how the piston was burned. I asked if he thought it could have been a bad O2 sensor and he didn't think so. But with the engine not being able to run right now well enough for them to know for sure if the high pressure fuel pump was bad what can I do to find out what caused this problem? They suggested a new power head or a new engine.

    If I buy a rebuilt one how much typically does it cost to install it? He said that I can't use my old injectors and fuel pump? Why is that? Can someone who is not a Yamaha mechanic install these things by himself or is that foolish to think? What all is involved in installing a powerhead? What else is needed?

    Without knowing what caused the first problem is it even advisable to get another one?

    Thanks for any help.
    Last edited by keithscatch; June 28th, 2007, 09:38 AM. Reason: Left out info
    Keith Tauber
    Palm Bay, FL

  • #2
    Re: 1999 Yamaha 0X66 powerhead blown help

    Sorry to hear of your blown power head. I had a similiar problem with one of my 1998 0X66 motors last year. I weighed the pros and cons of a new repower and a rebuild. I chose the rebuild option simply for economics - if I replaced one I'd likely replace the other. The motors had less than 800 hours.

    I used a certified Yamaha mechanic for the repair. He was able to reuse the injectors, pumps, and almost everything else. There were some items replaced but mainly the power head. The total cost...$ 8,000.00 and I'm very happy with the results. Good Luck.

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    • #3
      Re: 1999 Yamaha 0X66 powerhead blown help

      The likely cause is a fuel restriction. The pump can be tested as well as the injectors. Most shops send the injectors off to be cleaned and tested.

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      • #4
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        Re: 1999 Yamaha 0X66 powerhead blown help

        Thanks guys.

        One shop suggested that Ethanol could be the culprit. He surmised that ethanol cleans the gas tanks so well that it can loosen particles, rust, debris etc from the tank that has sat there for years and allow them to get into the fuel pass through the filter and get clogged into the injectors resulting in clogged injectors which leads to fuel restriction which leads to overheating of that 1 cylinder and thus piston failure.

        Is this a correct theory? It sounds plausible enough. If so, that is scary that there is so much Ethanol in our fuel that this sort of thing could happen. He said he was told that gasoline distributors and wholesalers are allowed to add as much as 15% Ethanol into our gas without telling us. Yet, everywhere I read says no more then 10% is in gas unless clearly marked and it is at 15%. In any event he said to install a 10 micron fuel filter and that would protect such a thing in the future. So if you all don't have one yet then install one.
        Keith Tauber
        Palm Bay, FL

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