07 YZ valve issue... need advice


11 replies to this topic
  • weedhopper

Posted July 22, 2009 - 08:10 PM

#1

Hey everybody, I need your input on an issue if you know what you're talking about. A while back the cam chain slipped a couple teeth on my 450. I believe I bent a valve very slightly and now I'm burning oil pretty copiously :worthy: . I open it up and a nice white cloud rolls out. It still runs good but something isn't right. I tore the motor down today and looking at the valve faces and top of the piston I pinpointed what I believe is the problem valve. It happens to be an intake valve. What exactly should I replace along with the valve if that's where the oil is coming from? I noticed that the top of the piston was covered in oil. If blow by due to bad rings was my problem the piston would be still be mostly dry right? Or would oil still settle on top of it? The cylinder and piston looked like they were in good shape but I might put a top end kit in anyway. Is there a good way to find out for sure if that valve is actually the problem? I don't have a compression tester and yes my valves are in spec.

  • grayracer513

Posted July 23, 2009 - 07:22 AM

#2

I noticed that the top of the piston was covered in oil. If blow by due to bad rings was my problem the piston would be still be mostly dry right?

Wrong. Smoke in the exhaust means oil in the combustion chamber. Simple.

You bent the valve, I assume you replaced it. It is possible that the valve guide and/or piston skirt was also distorted by this event. Have a shop do a leak down test, then tear down and inspect it.

  • mxmaddman

Posted July 23, 2009 - 08:02 PM

#3

When was the last time it was rebuilt? Its an 07 its probably hurting for a rebuild and a new set of valves. Does it happen to be the middle intake valve?

  • weedhopper

Posted July 25, 2009 - 09:02 PM

#4

It hasn't been rebuilt yet but I just ordered a top end kit and I'll give it a shot. I don't think there are any problems with the middle intake valve. Why do you ask?

  • mxmaddman

Posted July 26, 2009 - 08:19 AM

#5

Yea, it definitely should get a new set of valves and a rebuild. I ask about the middle valve because it seems to be the one that always goes out of spec first. Be sure to inspect the lower crank sprocket. when the cam chain slips it generally means its way out of spec. If the lower sprocket on the crank is worn out you will need to replaced the crank. That chain needs to be replaced at least once a year or it will wear and ruin the crank or jump timing as it did or both. check or replace the tensioner as well. Its seems excessive, but its all routine maintenance that is supposed to be done.

  • weedhopper

Posted August 02, 2009 - 02:01 PM

#6

Turns out all it needed was a new top end kit. No valves got bent when the cam chain slipped. Runs better than ever :thumbsup:

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  • mxmaddman

Posted August 02, 2009 - 05:22 PM

#7

Turns out all it needed was a new top end kit. No valves got bent when the cam chain slipped. Runs better than ever :thumbsup:


Its an 07 it most likely needed valves by now. I hope you don't find out the hard way.

  • mikedabike

Posted August 02, 2009 - 06:18 PM

#8

Its an 07 it most likely needed valves by now. I hope you don't find out the hard way.


You can tell based on the year of the bike? I have an 07 in my garage that only has about 50 hours should I change the valve? My brother has an 03 that has 300+ hours and has never had anything other than a valve inspection and they are still in spec. I am trying to get him to let me put in a chain and piston but I suspect the valves will be in spec from what I have seen with our other YZF's.

  • grayracer513

Posted August 02, 2009 - 06:40 PM

#9

Its an 07 it most likely needed valves by now.

There is no factual basis for that statement.

  • mxmaddman

Posted August 02, 2009 - 09:09 PM

#10

well I'm just saying if it was mine I would have for sure.. it obviously has enough hours on it to burn oil really bad and jump time. I would be putting a set of valves in for piece of mind. Better safe than sorry. I don't like playing Russian roulette. you guys can if you want, its your wallet...:thumbsup: when a bike jumps time or burns oil there's a reason behind it and most of the time its caused by wear, especially when it does both. Just because the valves are in spec now doesn't mean its not going to come apart on you next week.


Weedhopper you at least put a new cam chain in it right?

  • weedhopper

Posted August 03, 2009 - 01:54 PM

#11

Yeah I put a new chain in. That was the reason the timing was thrown off in the first place. The cam chain was junk. You can almost buy a used head for the price of having five valves replaced. I can't justify spending that kind of money if they aren't causing any problems. My last Yamaha had the same valves for 5 years without any trouble whatsoever. I have a feeling the guy I bought this bike from didn't take care of it well (air filter and oil changes) and that was the reason for the accelerated piston and ring wear. I have a tendency to get screwed over every time I buy a used bike. No matter how well I inspect it. People are just dishonest sometimes.

  • weedhopper

Posted August 03, 2009 - 02:01 PM

#12

You can tell based on the year of the bike? I have an 07 in my garage that only has about 50 hours should I change the valve? My brother has an 03 that has 300+ hours and has never had anything other than a valve inspection and they are still in spec. I am trying to get him to let me put in a chain and piston but I suspect the valves will be in spec from what I have seen with our other YZF's.


I would definitely at least put in a new chain on your brother's bike if it has never been replaced. It's cheap and simple. Unlike valves. Then he can avoid what happened to me, which could have been catastrophic had it slipped a little more.





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