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  1. #1

    Head gasket failure? 2000 xl800

    Yamaha xl800 less than 5 hours on SBT rebuild. 32:1 mix 3rd time out on the ski. Looking for some opinions on this top end failure. Does this look like a head gasket failure or just a result of lean carb jetting or setting. Engine died after a 30 minute ride on the lake at about 3/4 throttle for a good clip. Cruising around 5k to 6k rpm. It restarted ok but then failed shortly after and had to be towed in. See photos of the results. Any opinions appreciated. I did notice a missing part in the cooling port. Click image for larger version. 

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  2. #2
    raiderteen's Avatar
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    Doubt it was head gasket failure. How did the power valve look? Any chance it caught the piston/rings? Were the carbs rebuilt with genuine mikuni kits when new motor was installed? Strictly premix or still running oil injection?

    Also, that missing part you are referring to (I believe) is the sacrificial anode for corrosion control inside the cooling system. More so during salt water use than anything. Can see the one still installed in the MAG cylinder and the spot it mounts on the PTO cylinder in the third picture.

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  4. #3
    Quote Originally Posted by raiderteen View Post
    Doubt it was head gasket failure. How did the power valve look? Any chance it caught the piston/rings? Were the carbs rebuilt with genuine mikuni kits when new motor was installed? Strictly premix or still running oil injection?

    Also, that missing part you are referring to (I believe) is the sacrificial anode for corrosion control inside the cooling system. More so during salt water use than anything. Can see the one still installed in the MAG cylinder and the spot it mounts on the PTO cylinder in the third picture.
    After cleaning the power valve I noticed a sliver of metal missing near the pin end. The color is significantly lighter so it broke during the failure or caused it. Doesn't look like the main section of the pw hit anything. Im going to flush out the bottom and reassemble the motor.... after I fish out the debris.Click image for larger version. 

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  5. #4
    raiderteen's Avatar
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    That power valve didn't hit the piston. You'd know it if it did. Not sure what that mark is by the pin but doesn't appear to be related to anything here.

    Something else caused the failure. Why was the SBT motor installed to begin with? Were the carbs rebuilt at that time? If so what kits were used?

    Also, that debris in the lower end is enough that I would HIGHLY recommend pulling the motor and opening up the case to inspect bearings and properly remove debris. You wont be able to use a magnet to remove anything so slim chance you remove everything from above.

    At that little of hours/run time isn't there a warranty on SBT motors?

  6. #5

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    looks like lean detonation to me. either carb not set correctly or plugged up with gunk.

    edit: also 32:1 is not a good ratio for the 800. you have to think this way - if you add more oil you are making it leaner since less fuel is being taken in each stroke. people think extra lube is good but it leans out the situation and if carbs are not right it just adds to the lean condition.

  7. #6
    butterbean_29512's Avatar
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    Definitely lean detonation got that piston. From where...who knows? Did you rebuild the carbs and set them correctly? Maybe a bad crank seal. That's why there's a fault free warranty. When you get the new one back, definitely rebuild the carbs completely with genuine Mikuni kits, and set carbs to stock Yamaha settings. I'd put the oil injection back on it, but that's just me.

  8. #7
    boudin's Avatar
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    When you say "5 hours on SBT rebuild" do you mean you have 5 hours on a motor shipped from SBT, or a broken older SBT motor that you rebuilt and have 5 hours on?

    If the former, unfortunately you just voided the warranty by removing the head.

    Agree with others on rebuilding the carbs.

    -Greg

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