Yz400f. Valves tight

7 replies to this topic
  • missouri-man

Posted January 11, 2016 - 08:22 PM


So. I just put a full set of valves in my bike and. They are tight with small shims any ideas?


Posted January 11, 2016 - 09:33 PM


Assuming you got the correct valves. I bet either the seats have been worn down too far and/or the seats were machined down too far. The only way I can think to fix it is replace the seats or get valves with shorter stems. But I don't think you can get short valves. So replacing the seats is about it.

Is the problem with all the valves or just a couple?

I had this problem with a Honda, the head was machined so many times that the new valves had zero clearance with no shims in. So we just had new seats installed.

  • missouri-man

Posted January 11, 2016 - 09:39 PM


That's what I was thinking. And. It's with them all. IV worked on alot of thes e and never had this problem. Any idea on changing the seat. Somthen a guy can do at home

  • grayracer513

Posted January 12, 2016 - 07:02 AM


Replacing seats requires the old seats to be removed first.  This is variously done by boring them out of existence, or a couple of different methods of pulling them from the head using heat and other equipment. The new seats ten have to be cut concentric with the valve guides.  A specialized job, to be sure.


How small are the shims? 

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  • missouri-man

Posted January 12, 2016 - 10:10 AM


1.72. And. With no shim just bucket I have .45 mm gap

  • grayracer513

Posted January 12, 2016 - 11:28 AM


Yup, sounds like the seats are cut too deep.

  • missouri-man

Posted January 12, 2016 - 04:59 PM


Any idea were I can get new seat. Will 450 seats fit?

  • grayracer513

Posted January 12, 2016 - 09:00 PM


Check with the local bike shops to see who they send their machine work to.  If you can't find someone local, there is Millennium Technologies and Engine Dynamics you can send out to.  Also Fast Heads. 

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