Valves IN&EX - how long do they last?



3 replies to this topic
  • thefex

Posted October 01, 2014 - 01:32 AM

#1

hi
i`ve got an YZ450F 2008 during engine rebuild. I assume that the motorcycle may have 250-300 moto-hours already, but can`t tell it precisely (when I bought it I`ve mounted the motohour counter and done 100 mth myself).

The question is:
how can I check if the TITANIUM intake & exhaust valves need replacement?
I took them out - they look fine, no scratches, the contact surface of the valve and seats looks ok. the engine has compression and doesn`t burn oil.

I`m only affraid that the valves may one day brake apart and make a huge mess in my rebuilt engine. But the titanium valves are quite expensive, you know the pain... 

I don`t have any pics of the valves and head at the moment, but here`s a pic of the engine with new bearings and PROX crank

bikepics-2699460-800.jpg

bikepics-2699458-800.jpg


Edited by thefex, October 01, 2014 - 01:36 AM.


  • grayracer513

Posted October 01, 2014 - 07:22 AM

#2

Looking at the sealing face of the valve, if you can detect any sort of ridge at the edge of the bright contact/wear stripe, the valve should be tossed.  One one your best clues as to the wear is how much you have had to adjust them up to now.  If you never have because they're still in spec, just run them.  Do be sure that they go back in their original seats, though.  Don't mix them up.

 

Ti valves depend on a hard coating to be hard enough to last in service.  The coating is so hard that it's impractical to machine it, so it has to be applied in a very thin layer (usually .001" or less).  Once the coating wears through, the valve wears very rapidly.  It also usually doesn't wear absolutely evenly, which makes it scrub laterally as it hits the seat, and that is one of the two main reasons valves break in YZF's (the other being timing chains jumping).  If you're worried about them failing, replacing them will fix that, but usually, you'll be OK as long as you don't try to keep using a valve whose shim size you've reduced by two sizes or more.



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  • thefex

Posted October 02, 2014 - 11:35 PM

#3

thank you Gray, your posts are very helpful.

I already bought a new Yamaha valve set +springs +seals for $300. The cylinder head will go to a machine shop for measurements. I know that the valves can not be lapped and all the work should be done only to the valve seats. Is there anything that I should tell the machinist before he starts working on the head?

and one more question:
one guy mentioned on a yz forum that along with the valve set, both the retainers (#7 and #8) and cotters (#9 and #10) should be replaced... That`s another $100. I would rather not change them... what`s your opinion?

 bikepics-2700056-full.jpg


Edited by thefex, October 02, 2014 - 11:38 PM.


  • grayracer513

Posted October 03, 2014 - 06:48 AM

#4

Unless there is visible, significant evidence of wear in the tapered center bore of the retainers wear the keepers (cotters) rest, like they've "sunk into" the retainers some what, there's no particular reason to replace the retainers.  Replacing the keepers is a good idea, though.







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