yz timing question? which mark is TDC?

8 replies to this topic
  • yamahahahaha

Posted March 23, 2004 - 05:06 PM


When I open up the little view plug on my case to show the TDC mark I find two marks. There is an I or H type mark, then as I rotate the engine slightly there is a straight line right next to the I or H or whatever it is. Which of these marks is the correct mark to line up in the window?


  • tctrailrider

Posted March 24, 2004 - 02:57 AM


The I

  • jchantzWR400F

Posted March 24, 2004 - 04:38 AM


I second that....look for the "I" mark.

  • SXP

Posted March 24, 2004 - 04:48 AM


....or with the plug out, drop a thin screwdriver down the plug hole and watch it as you turn the crank - when the piston is at TDC, the screwdriver will be at it's highest point. Peek through the view plug hole and you should see the "I" mark lined up with the notch. This will happen every revolution of the crank, but the cams will be lined up for valve clearance measurement every other revolution.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • yamahahahaha

Posted March 24, 2004 - 05:06 PM


I have the service manual and the picture it shows looks more like a straight up and down line...like the one next to the I or H or what ever it is...They are so close together though....like and eight of an inch or so, does it even matter which is in the window?


  • jchantzWR400F

Posted March 25, 2004 - 03:55 AM


It actually says "HI" you will want to line the "I" in "HI" up in the window. The "I" will be straight up and down just like in the manual.

  • yamahahahaha

Posted March 25, 2004 - 12:40 PM


thank you very much....that is what I thought :)....I just wanted to make perfectly sure before I screwed something up...


  • Hamish

Posted March 25, 2004 - 07:44 PM


They are so close together though....like and eight of an inch or so, does it even matter which is in the window?

That 1/8" equates to about 5-10deg crank rotation, so in answer to your question, yes it does matter. Due to the fact that the piston hovers at TDC for a little while, the screwdriver method isn't very accurate. Try a piston stop and degree wheel to check it accurately.


  • Andrea

Posted March 28, 2004 - 07:40 AM


sorry but i have a page of dirt bike magazine where explains whether to put yz timing, and TDC is "H"



Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.