yz400 loose exhaust valve specs


9 replies to this topic
  • 90atk

Posted February 28, 2015 - 07:34 AM

#1

im getting .017" and .015" on the exhaust valve clearances with .012" being the max. is it possible anything got damaged? should i check anything else while i have the cam out? all the intakes were in spec.



  • WilfulLemar20

Posted February 28, 2015 - 10:33 AM

#2

I have a world of trouble with my vavles also have you tried changing the shims out for a bigger size should be able to tighten up your clearances with new shims

  • grayracer513

Posted February 28, 2015 - 12:09 PM

#3

YZ400F valve clearances are:

Intakes: .10-.15mm (.004-.006")

Exhaust: .25-.30mm (.010-.012")

 

*Gently* tap downward on each bucket while the lobes are facing up away from them to "bounce them shut", then retake your measurements.  Could be just carbon on the stem holding them up.  Usually, they don't loosen, they tighten.  You might inspect the tops of the valve stems for wear or "mushrooming".  Reshim as needed. 



  • WilfulLemar20

Posted February 28, 2015 - 01:29 PM

#4

So because the vavle shims get hit in the center in causes a mushroom effect and that's why they tighten when they where? I have been curious about this sorry for getting off topic

  • 90atk

Posted February 28, 2015 - 05:10 PM

#5

well i didnt know about the tapping trick. when i first got the bike they were on the loose end .013 i think but i rode it anywase. now im getting bigger. but i allready pulled the cam out and got some bigger shims so well see what happens when i get the cam back in hopefully its not too tight now. the previous owner did install hot cams with the auto decompression.



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  • grayracer513

Posted February 28, 2015 - 09:00 PM

#6

So because the vavle shims get hit in the center in causes a mushroom effect and that's why they tighten when they where? I have been curious about this sorry for getting off topic

 

No, that's why they would get looser.  The normal pattern is that the sealing face wears where it contacts the valve seat, which lets the valve move up into the head farther, closer to the cam, and therefore tighter cleareance.



  • WilfulLemar20

Posted February 28, 2015 - 09:05 PM

#7

So the bigger the shim you would put in would open the clearances up? Sorry I am just new to a set up like this want to get my bike right before spring

  • grayracer513

Posted March 01, 2015 - 08:32 AM

#8

The shim goes into the space between the valve stem and the lifter, so the bigger the shim, the tighter the clearance.

 

http://api.viglink.c...ech/valves.html



  • WilfulLemar20

Posted March 01, 2015 - 12:34 PM

#9

Alright thats what I thought but was not cartain thanks for the info

  • 90atk

Posted March 02, 2015 - 06:10 PM

#10

well i got it all back together. the way i figured it out on paper i was supposed to end up with .011" but it ended up being .010" so its on the tight side but the next size down shim would have made it on the loose side so i left it. hopefully it doesnt tighten up on me. ill keep an eye on it. and i only droped that c clip thing down in the motor once. i got it out pretty easy thankfully.







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