yz125 blown head gasket?

Discussion in '2-Stroke Discussion' started by danielhrnr, Jun 1, 2009.



  1. danielhrnr

    danielhrnr Rookie DRN Member

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    Whats up guys


    I have a 2002 YZ 125. I just did a new top end on it about 7-9 hours ago, with that said. Last night I was doing my regular maintenance oil change, spark plug, all that good stuff. every time i do the maintenance i like to do a compression test (the plug is already out so why not). The compression was a little low about 130psi. So i was looking into why it was so low and noticed when it was running coolant was dripping out of the over flow tube from the radiator. I took the radiator cap off and saw bubbles coming out of the top of the coolant.



    This means the head gasket is bad right?
    The oil I drained out was normal color it wasn't milky or anything like that, the exhast never smelt like coolant, and the plug looked normal.

    So i guess i want the some advice as to if it is the head gasket or not.

    Thanks in advance for the help.



    And does any one know what to torque the head bolts at.
    Last edited: Jun 1, 2009
  2. Matt90GT

    Matt90GT Rookie DRN Member

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    call your local dealer for the torque specs

    The cylinder head does not use a gasket. But 2 O rings. If the head is torque to spec properly, then you either have a warped head or cracked head and/or cylinder. it could also be installer error pinching the O rings

    To fix the head, have a machine shop mill it down .010". Give you a bit more compression also. But you may want to have someone magna flux the head and cylinder to see if there are cracks in it first.
  3. danielhrnr

    danielhrnr Rookie DRN Member

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    Well I took the head an cylinder to the machine shop today and they said everything was fine nothing is warped (thank god). And the torque specs i had when I did the top end were right. So I'm guessing it was mu fault when I installed the o-rings when i did the top end.

    Do you guys have any tips on getting the new o-rings to seal this time around?
  4. Matt90GT

    Matt90GT Rookie DRN Member

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    put a small amount of grease in the grooves where they lay. It will help keep them down while you install the head.

    you may still have a problem with the cylinder. Sounds like you did not get it fluxed.

    I was rereading your original post, you may want to inspect the water pump impeller also and seal there. Maybe it is cavitating or leaking.
  5. danielhrnr

    danielhrnr Rookie DRN Member

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    Sorry i forgot to add that they did flux the head and there were no cracks.

    I'll pull the water pump off today and check the impeller.

    Thanks for the help.
  6. spark250

    spark250 Rookie DRN Member

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    You can't flux aluminum...
  7. danielhrnr

    danielhrnr Rookie DRN Member

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    That's right! So it got me thinking. So i called the machine shop and he said he used something called zyglo flux witch is a florescent penetrate for aluminum.



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