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water getting on my top of my piston!

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I have an 09 yz250f and i had to rebuild it cause i had a brand new piston grenade and had it bend a rod and two valves. so i got all the parts and put it all back together and torqued down my head put the motor in and rode it up and down my driveway for an hour and i thought it was all good running fine so i loaded up and went to the track i got on and when i opened it up and it started running bad when i exited the corner and the engine breaking was really aggressive and it shot a bunch of water out the overflow and i took it home and my head bolts had come loose so i tighten them and it did the same thing again and all the threads are good. so i guess my question is it common for head bolts to stretch??? please help

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What do you mean by stretch? Are they longer than normal?

Yes, it is common for bolts to stretch. It happens slightly every time you torque a bolt, that is what torquing is for! Did you torque the bolts to the spec in your manual? If not that could be why they are coming loose. Torquing to spec is very important, especially on engines with all their vibration! Use a torque wrench, if you over do it, especially in aluminum, you will pull the threads right out of the engine and be screwed! Do it Goldilocks style, not too much not too little, just right.

I assume you are talking about water from the cooling system getting in. You will need to replace the oil, coolant can do bad things to oil. You should also replace your coolant if oil got into that.

Did you make sure all of the gaskets are in place?

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replace the bolts, as for the water, make sure gasket is in place or replace the gasket

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yea i torqued to spec and but the water isnt getting into my oil. illl try some new bolts and see if that works.

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Oops, I thought you meant water came out the vent at the top of the head cover. It sounds like the bolts came loose and it might have blown out the inside of the head gasket so compressed gas would be going into the cooling ducts. Would also explain the engine breaking if it was taking the bang out of your power stroke.

As stated above, replace the bolts, make sure the gasket is intact and in good order and tighten to spec. I would probably replace to coolant, too.

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