yz400f rebuild timming

2 replies to this topic
  • fridder

Posted October 19, 2005 - 09:14 AM


I'm rebuilding my 400f (1999) after a major melt down. In the process of putting it back together the timming chain came off of the lower sprocket I thought it was no big deal but now I cant seem to get the prick marks on the cam sprockets to line up with the deck of the head when the timming mark is within the viewing window. If I move the chain on the cam sprockets one tooth Im too far on the timming mark and when I move the chain back I'm too early on the timming mark. Is their a difference between moving the chain on the cam sprockets and moving the chain on the lower sprocket like it would give me a smaller amount of ajustment to get the prick marks on the cam sprockets to line up with the head deck and the timming mark at least closer. Is it beter to have the timming mark lined up before the cams get to the proper location or have the mark be past. Also is it possible that with the meltdown I should be checking the woodriff key on the timming gear shaft, maybee thats why Im having such a hard time with the timming.

Thanks for any help
matt toledo ohio

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  • 93gt

Posted October 19, 2005 - 10:16 AM


Maybe your timing chain is stretched. I didnt see that you bought a new one, so this could be the reason its not lining up just right.

  • grayracer513

Posted October 19, 2005 - 10:31 AM


You can confirm TDC by running a stiff wire probe down the spark plug hole. Also, be certain when timing that the slack in the front run of chain is drawn out by pushing in on the chain tensioner. Rotate the engine and the cams slightly backwards from TDC and then roll the crank forward. Bear in mind that the timing marks will not line up perfectly under normal circumstances, and you have to look at them and visualize what it would be like for the mark to be one tooth in either direction from where it is.

As for the timing chain, it should be replaced just for maintenance. You did do that, right? It's not too late.

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