Jump to content

2008 YZ450 valvetrain issue

By XT2YZ,
in YZ400F/426F/450F/450FX

 Share

Recommended Posts

Enthusiast

XT2YZ

Posted
Posted

I have a stock 2008 YZ450 with 26 hours on it. I use Amsoil MCF and change it every five hours. I have not been into the motor. Recently I have been getting some loud ticking, almost a clacking, out of the top end. It comes and goes, almost like something is stuck and then frees up. Yesterday (Sunday) I started it and there was no noise. I let it warm up for a minute. As soon as I gave it some gas I got the sound of really loose valves. If I rev the motor just a few thousand rpms it fades, then I hear it again at idle. I went out for practice and when I came back, no more noise. No more noise for the rest of the day. It did the same thing last weekend but I also rode Saturday with no occurrence.

I am hoping someone might shed some light on this before I go digging. Any input is appreciated.

Link to comment
Share on other sites
Grand Master

grayracer513

Posted
Posted

Normally, most of the noise in a YZ450 is generated in the primary drive gears and transmission, and not so much in the valve train. Having the noise diminish by raising the engine speed higher than idle supports this, as it is the fact that the engine does not truly run at a steady speed at or near idle that causes all the rattling. However, the valve train could be involved.

Start by checking the clearances. Then, while you have it open, do a quick inspection of the tensioner and chain:

  • Position the engine at TDC with the cam lobes pointing up and out, not down and in.
  • Remove the center cap screw from the tensioner (see page 4-18 of the manual).
  • Insert a small screwdriver into the slot in the tensioner under where the center screw was and rotate the tensioner drive shaft clockwise as if tightening it. There will be spring tension resisting you, but it should move freely, and when released, it should return smoothly to it's original position.
  • Wind the tensioner in a way and hold it. Push downward on the cam chain between the two cams to create some slack, and check that the accessible links seem free and do not bind or kink.

If you have any doubts regarding the tensioner, you can remove it and inspect it further, or just replace it.

Link to comment
Share on other sites
Enthusiast

XT2YZ

Posted
  • Author
Posted

Start by checking the clearances. Then, while you have it open, do a quick inspection of the tensioner and chain:

  • Position the engine at TDC with the cam lobes pointing up and out, not down and in.
  • Remove the center cap screw from the tensioner (see page 4-18 of the manual).
  • Insert a small screwdriver into the slot in the tensioner under where the center screw was and rotate the tensioner drive shaft clockwise as if tightening it. There will be spring tension resisting you, but it should move freely, and when released, it should return smoothly to it's original position.
  • Wind the tensioner in a way and hold it. Push downward on the cam chain between the two cams to create some slack, and check that the accessible links seem free and do not bind or kink.

If you have any doubts regarding the tensioner, you can remove it and inspect it further, or just replace it.

So, the valves are all in spec. The cam chain seems fine as well. I removed the chain tensioner. When I turn it in and release, it comes back out smoothly. Except for when I turn it all the way in. Then it sticks. It will not let loose and return without some help. Does the tensioner, under normal operation, ever max out like that? If so, it is definetly not working correctly and may be the culprit. Either way, it is highly suspect and I'll be replacing it.

Link to comment
Share on other sites
Grand Master

KJ790

Posted
Posted
So, the valves are all in spec. The cam chain seems fine as well. I removed the chain tensioner. When I turn it in and release, it comes back out smoothly. Except for when I turn it all the way in. Then it sticks. It will not let loose and return without some help. Does the tensioner, under normal operation, ever max out like that? If so, it is definetly not working correctly and may be the culprit. Either way, it is highly suspect and I'll be replacing it.

Your tensioner sounds fine. They all stick when backed off all the way, this way you can reinstall it without having to hold it backed off the whole time. In operation the tensioner should never be near that far in.

Link to comment
Share on other sites
Enthusiast

XT2YZ

Posted
  • Author
Posted
Your tensioner sounds fine. They all stick when backed off all the way, this way you can reinstall it without having to hold it backed off the whole time. In operation the tensioner should never be near that far in.

OK, perhaps I was a bit hasty when I inspected the chain. After reading your post I went back out to the garage and the chain is now the "highly suspect" component. I am having trouble locating a specific link or links that are binding but when I rotate it there is a spot where the chain won't seat properly in the cam sprocket.

Link to comment
Share on other sites
Community Regular

davcon

Posted
Posted
What type of flywheel puller will I need for replacing the chain. I mean, is it specific to the bike?

I just bought and used this one: http://www.rockymountainatvmc.com/productDetail.do?navType=type&navTitle=Engine&webCatId=17&webTypeId=203&prodFamilyId=17329&stockId=143963#vehicleSelect

Read this also https://www.thumpertalk.com/forum/showthread.php?t=568177

Link to comment
Share on other sites
Enthusiast

XT2YZ

Posted
  • Author
Posted

Well, replaced the cam chain. It had two links that were binding. Unfortunately, this did not solve my problem. My engine is still making the same noise. Any other ideas? The more I listen to it, I'm starting to think it sounds like the piston. I have ridden the bike four or five times since I first noticed it. Sometimes it doesn't make the noise at all. Other times, it will just sort of come and go. It has always run fine and never given me any sign of a problem besides the noise.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

ThumperTalk

Register a new account Sign In Now
 Share
Go to topic listing
×
×
  • Create New...
Terms of Use
Copyright
Privacy Policy