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chasehoskins91

yz450f burning oil

7 posts in this topic

Hey guys i've got a 2007 yz450f that i bought from a guy and didn't realize how much oil it was burning. I had the top end rebuilt thinking it would solve the problem and it hasn't. I'm thinking that my piston clearances are off and i'm going to tear it down again tonight and check them... do you guys know of anything else it could possibly be? just want to cover all my bases and check everything before i put it back together. It burned about a quarter of a liter in an hour of riding so quite a bit. Any input is greatly appreciated. 

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There are only two paths for oil to enter the combustion chamber by: The piston rings and the valve guide seals. 

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There are only two paths for oil to enter the combustion chamber by: The piston rings and the valve guide seals.

Gray can I replace the valve seals with the engine still together other then pulling off the valve cover? Or do I have to pull apart the top end and do it on my work bench? I don't have a new gasket at this time so if I could do it without the valves falling in the cylinder that would be nice.

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It's "possible" but it's a question as to whether or not it's easier.  I know one guy who did it once and said he probably wouldn't again.

 

You would need to find or build an adapter to connect compressed air into your spark plug hole.

  • Remove the cams, support the cam chain and rotate the engine to bottom dead center
  • Apply ~60-70 psi of air from a compressor or other continuous supply to the plug hole
  • Remove the valve springs
  • Replace the seals and reassemble

The air pressure will hold the valves up and closed.

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It's "possible" but it's a question as to whether or not it's easier.  I know one guy who did it once and said he probably wouldn't again.

 

You would need to find or build an adapter to connect compressed air into your spark plug hole.

  • Remove the cams, support the cam chain and rotate the engine to bottom dead center
  • Apply ~60-70 psi of air from a compressor or other continuous supply to the plug hole
  • Remove the valve springs
  • Replace the seals and reassemble

The air pressure will hold the valves up and closed.

 

Or you can do what an old mechanic showed me. Take the spark plug out, put some nylon cord in the chamber through the hole, and roll the kick start until the cord is pushed up against the valves. It work very well and the holds the valves better that air so you don't have to worry about losing the seal, if you even have enough of a seal.

 

All that being said, I never had a good reason not to just pull the head off and do it right. It doesn't take too long and you may even find something else that needs fixing.

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Holding up the valves is one thing and it can be done. The harder issue would be to compress the valve springs and remove the retainers then reach down there and pull the seals. Let alone put the seals back in.

It should be much less frustrating to pull off the head and do it.

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Haha alright thanks guys I'll wait for a gasket and pull the head off again. Glad I asked.

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