How do I know when I need to get my 426 head redone?

[jcm3]

My 2001 runs great, and is a first kick starter about 9 times out of 10. I don't have any complaints, but ass-u-me that the head has not been redone.

I'm considering doing the top end and the head, just so that I know that it is fresh. Even if I pulled it apart, I don't know what to look for to determine if it needs a valve job and new parts.

I'm a pretty competent bike mechanic, so I will have no problems tearing everything down and putting it back together. I just don't know what to look for.

Can I assume that if it starts right up and runs great that it is probably ok? Money is a bit tight to do it all right now anyway, but I'd 'like' to.

[grayracer513]

The key to it is valve clearance. Your bike uses titanium valves, which depend on a very thin, extremely hard coating for their wear resistance at the valve face. There are two important signals you can get from checking the clearance, and from knowing its history:

• When any valve closes up to the point that it needs a shim .10mm or more smaller than what it started with, a valve job is needed, or will be very soon.
  
• When a valve is adjusted, but then is found to have tightened up again in less than 10 hours, the hard coating is gone, and the valve needs replacement.
  

Running Ti valves beyond this point runs a very real risk of a valve stem failure, and the general destruction of the engine.

[jcm3]

Thanks. I'll pull it apart and check the clearance, and also check to see if there are currently any shims in there.

I appreciate the info.

[grayracer513]

(I'll) check to see if there are currently any shims in there.

Of course there are. Need a manual?

http://www.yamaha-motor-europe.com/community/service/manuals.jsp

[jcm3]

Of course there are.

You know what I meant.

• When any valve closes up to the point that it needs a shim .10mm or more smaller than what it started with, a valve job is needed, or will be very soon.
  

[grayracer513]

You know what I meant.

After a couple of the questions that have been asked around here recently, no, I assume nothing.

[rufusz]

When any valve closes up to the point that it needs a shim .10mm or more smaller than what it started with, a valve job is needed, or will be very soon.

On a bike that was bought used how do I know what it started with? Do they come out of the factory with the same (standard) shim size?

[grayracer513]

On a bike that was bought used how do I know what it started with? Do they come out of the factory with the same (standard) shim size?

You don't. In that case, you can only go by the second criteria.