How close is enough with valve clearance?


14 replies to this topic
  • Indiana

Posted September 24, 2006 - 04:08 PM

#1

I have a 03 YZ450. This bike is new to me so I did a valve check today. Everything was within specs except the left intake valve. It measured .005 too tight of being within specs. Should I re-shim or not worry?

Also, why the hell does they service manual tell you to remove the carb for this procedure? I didn't and didn't see the need. I had to remove enough stuff without any extra work.

  • mobius

Posted September 24, 2006 - 04:22 PM

#2

If it was mine I would keep everything shimmed within spec. That is why the manuel gives some room with their numbers, don`t exceed those numbers. I would not worry about the carb.

  • 642MX

Posted September 24, 2006 - 04:37 PM

#3

You need to keep them within spec. :thumbsup: Reshimming the valves is not very hard. Just take your time and watch what your doing.

  • grayracer513

Posted September 24, 2006 - 07:48 PM

#4

.005 what? If it's .005" too tight, that's way off. The specified range, .10-.15mm, is not quite .002" wide. If it's .005mm, I'd like to know how you think you measured a discrepancy of .0002" with a feeler gauge.

Since I'm pretty sure you meant .005", that has to be fixed. What's worse, unfortunately, is that it spells trouble. Being .005 too tight means that the shim size on that valve needs to be cut by .15mm to get it into spec (.005"= .127mm). That means that the hard facing on the valve is worn through, and the valve needs to be replaced. As further evidence, if you don't believe that, you will find it out of spec again in less than 6 more hours of riding. Just don't run it until the valve head drops off.

  • Supafreak_711

Posted September 24, 2006 - 07:55 PM

#5

Not to jack your thread but I had a question directed at grayracer, but anyone can answer. If I bought both of my bikes used and only have checked and shimmed them once... should I just keep an eye on the valves (I will have time to look at them again around X-mas time, last check was about a month ago). If they move again is it safe to say that they need to be replaced (even if they havent moved enough to tell me that I really need to replace them)?

  • grayracer513

Posted September 24, 2006 - 08:26 PM

#6

How much did they move? One shim size? That could have been seat wear, and in that case, you're probably OK. The trouble is that unless you check, you won't know whether they're holding their adjustment or not. I don't know how much ridimg you plan on doing between now and Christmas, but if they needed a re-shim, you should do a follow up check within 10 hours.

  • Indiana

Posted September 25, 2006 - 03:44 AM

#7

It was roughly .005 mm too tight. I guessing because I could force .1 mm gauge in and .092 slightly loose. That's my point at that close of a distance is that discernable. I notice in the manual they have you round to get the correct shim size. I'll all for maintaining just wasn't sure what is necessary. Thanks for the advice.

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  • Supafreak_711

Posted September 25, 2006 - 07:12 AM

#8

How much did they move? One shim size? That could have been seat wear, and in that case, you're probably OK. The trouble is that unless you check, you won't know whether they're holding their adjustment or not. I don't know how much ridimg you plan on doing between now and Christmas, but if they needed a re-shim, you should do a follow up check within 10 hours.


Ok, that helps alot. Actually I just remembered that I have checked the 450f twice, and only had to shim it the first time (they had stayed put since the first). So the 450f is probably ok until Christmas. The 250f I'm more worried about. Its a 01 that was raced by a previous owner and could probably use a rebuild (but I wont have time until Christmas...). This was the first time its valves were checked since I have owned it (it hasn't been ridden much in the past year, but I will admit to neglecting it before then). One intake valve's clearance was way tight and the rest were fine, so I guess I will be checking that intake again soon. Hopefully I can convince my dad its worth it to go ahead and rebuild the top end around x-mas time. I'm sure its cheaper to go ahead and replace the valves/piston BEFORE it blows up :thumbsup:

For the record... I'm pretty much anal about maintenance, but for some reason I was intimidated by the valves and didn't learn how to check them until the beginning of the summer this year.

Indiana: sorry for side tracking your thread

  • grayracer513

Posted September 25, 2006 - 08:50 AM

#9

... I have checked the 450f twice, and only had to shim it the first time (they had stayed put since the first).

The fact that the clearance have remained stable indicates that the reason the clearance closed up was intitial seat wear, and that the valves are likely in good condition. If they had continued to close up, that would have meant the valves were worn out, as I said. I would think the 450 was OK, too.

One intake valve's clearance was way tight and the rest were fine, so I guess I will be checking that intake again soon. Hopefully I can convince my dad its worth it to go ahead and rebuild the top end around x-mas time. I'm sure its cheaper to go ahead and replace the valves/piston BEFORE it blows up

When they are "way tight", that usually means trouble, since the typical thickness of the hard coating on the valve face is 2-5 microns (1 micron=1/1000mm=.000015"). The coating is outrageously hard and extremely durable, but IDLF (it doesn't last forever). In case your dad or anyone else has trouble seeing how this can lead to a broken valve, instead of just a very badly worn one, let me explain how that happens:

In a perfect world, the seat would wear into the valve face in a perfectly uniform pattern all the way around the valve. The world is not perfect, however, and if a valve wears more on one side than the other, the valve tries to scrub sideways as it seats. That flexes the valve stem, and if it flexes too much for too long, the stem breaks, turning the valve head into a 30 horsepower axe blade running loose in your combustion chamber.

Pictures of Valve Wear

  • Supafreak_711

Posted September 25, 2006 - 09:50 AM

#10

The fact that the clearance have remained stable indicates that the reason the clearance closed up was intitial seat wear, and that the valves are likely in good condition. If they had continued to close up, that would have meant the valves were worn out, as I said. I would think the 450 was OK, too.
When they are "way tight", that usually means trouble, since the typical thickness of the hard coating on the valve face is 2-5 microns (1 micron=1/1000mm=.000015"). The coating is outrageously hard and extremely durable, but IDLF (it doesn't last forever). In case your dad or anyone else has trouble seeing how this can lead to a broken valve, instead of just a very badly worn one, let me explain how that happens:

In a perfect world, the seat would wear into the valve face in a perfectly uniform pattern all the way around the valve. The world is not perfect, however, and if a valve wears more on one side than the other, the valve tries to scrub sideways as it seats. That flexes the valve stem, and if it flexes too much for too long, the stem breaks, turning the valve head into a 30 horsepower axe blade running loose in your combustion chamber.

Pictures of Valve Wear


Thanks for the great post, I will definately let my dad read it and consider rebuilding our 250f. I guess I need to start doing some research on what all I should replace (I'm sure if I dont find it there will be a new thread posted about it soon :thumbsup: )

Thanks again :lame:

  • Indiana

Posted September 25, 2006 - 09:56 AM

#11

You can jack the thread anytime at all. I would still like to know if the .005mm tightness warrants re-shim. Also, If I re-shim does it make any sense to just get the whole shim kit full of all different size shims for $100 or just buy shims as needed? I know the downtime would be less if I had them on hand. I just don't know how often I'll really need them and how universal they are. I currently have three bikes to maintain.

  • grayracer513

Posted September 25, 2006 - 10:36 AM

#12

I'd still like to know how you arrived at the conclusion that your valves are .005mm tight. I'd be stunned to find anyone who can measure that difference accurately with a feeler gauge.

Technically, specs are specs, and if you are outside the specified range, you should adjust for that. However, if you have a situation in which a .05mm gauge fits, but a .06 does not, you can call that good. If the .05mm has to be forced under the cam, then it isn't really fitting, and you should call it .04, which is out of spec.

Even though English gauges are not precisely correct, you can do the same thing with a .004" gauge. If the .004" fits, but the .005" doesn't, it's .004".

  • Indiana

Posted September 25, 2006 - 04:48 PM

#13

Thanks, like I said earlier there was an .008mm gap in my gauges. I am merely guessing at .oo5 tight. The .10 would go but I thought was a little tight to call it good and the .092 gauge was what I felt was too loose. I believe that if I were had a guage reading .095 .096 it would have felt correct. No matter, I hear what you're saying it just seemed awfully close to being within spec

  • gary81

Posted September 26, 2006 - 05:28 PM

#14

DOSE ANYONE HAVE A 2001 426 VALVE SHIM CHART THAT COMES FROM YAMAHA?I NEED SOME SHIM SIZES .
I HAVE A 179 AND A 178 ON EXHAUST WITH A .28mm CLEARENCE.ON BOTH
AND A 184 ,182 AND A 185 ON THE INTAKE WITH A .10mm CLEARENCE.ON ALL 3 INTAKE VALVES? WHAT SIZE SHIMS DO I NEED?
THANKS

  • grayracer513

Posted September 26, 2006 - 06:56 PM

#15

Put two 185's in the exhaust. The intakes are perfect just like they are.

AND STOP YELLING ABOUT IT.

:thumbsup:





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