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Hey everyone! So I just rebuilt the top end on my 05 400ex. I bored it to a 416, ported the head, new valve seals and a new cam. Got it all back together and fired it up and was running amazing across the yard for about 3 minutes and then it just started blowing smoke like crazy out of the exhaust. Any ideas what the problem could be here? I'm stumped because I checked everything when I had it torn down and it all looked perfect and all went back together perfect. Thanks in advance for any help!
 

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Did you do gt thunder head studs? Get the head skimmed? And did you torque everything properly? Sounds like it blew a headgasket. Also did you stagger the rings properly? Do a proper break in procedure? Was the piston and cylinder checked for proper clearance by a competent engine machine shop? Sorry lots of questions. But lots of possibilities here.
 

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Yes I got the GT thunder head studs. Sent the cylinder and piston to a local shop to be bored to match each other. I didnt have the head skimmed but never had any leaks from the gaskets do i just cleaned the surfaces real good before putting it back togethet. I got the rings on the piston properly and everything was torqued to spec. Was starting the break in process when this happened. Wasn't hammering the throttle or anything, just putting across the yard to make sure everything sounded and ran right.
 

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And it was burning a lot of oil before the rebuild. I could hold my hand behind the exhaust and hammer the throttle one time and it would spit a little oil on your hand.

I have pictures of the rebuild but I can't upload them on here for some reason if you would like to see some of them I can email them or something.
 

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If it was burning that much oil before the rebuild I would guess that your pipe heated up and started burning the old oil out. I've seen this before myself. After riding a bit the smoke stopped.

Rob
 

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Thats what i was hoping but I let it sit in the driveway and run for a little while after i parked it and it never showed any signs of getting better. This is part of the reason why I'm stumped. Gonna start tearing it back down today and checking everything again I guess.
 

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That sucks, hope you find the cause.

Rob
 

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Yes I got the GT thunder head studs. Sent the cylinder and piston to a local shop to be bored to match each other. I didnt have the head skimmed but never had any leaks from the gaskets do i just cleaned the surfaces real good before putting it back togethet. I got the rings on the piston properly and everything was torqued to spec. Was starting the break in process when this happened. Wasn't hammering the throttle or anything, just putting across the yard to make sure everything sounded and ran right.

When you pulled the head off originally did you untorque in steps or just remove each bolt all the way. You could have warped the head sligtly if you did the second option. That is why you get the head skimmed or run a virgin file across it to make sure its nice and flat. Or you will blow headgaskets. Odd thing is usually the gt thunder studs fix the warp anyway. Did you get a valve job done on it? Check valve guides?
 
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