HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
90atk

yz400 loose exhaust valve specs

10 posts in this topic

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0