YZ 426 Cam Timing Wrong in Manual ???

4 replies to this topic
  • NewfieWR

Posted June 03, 2005 - 06:43 AM


I just replaced the shift forks in my 426 & get to the cams....no biggy....so i thought :) .............followed the manual & cannot get good compression worked perfectly before the tear down.
What are the other dots without lettering on the cam sprockets ? :D lined them up in the middle, & had loads of compression :D ....but i may have flooded the bike or something, & like an ass.....screwed with the cams again thinkining that they were off timing :D .....never did get compression back after that.
Even done the 180 turn around on da cams :D
Must of bent the valves or something :D
I even removed the decompression all together :)

The manual is definately wrong....i've done loads of valves & stuff in my time :D


  • MAC426

Posted June 03, 2005 - 07:34 AM


To check your cams, you need to make sure your E on the exhaust cam is facing the exhaust port, and the I on the intake cam is facing the intake port. And simply align those two dots with the head surface. There are two dots on each cam ignore the inner two. They will sit slightly out of sight. To begin make sure you line up the TDC mark on the rotor in your sight window, those marks look different than the manual on my bike. Check your valve clearance, and you should be good.
In regards to the potential problem, you'll need to take your head off to be sure nothing is destroyed. Good luck.

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  • lumpy790

Posted June 04, 2005 - 09:17 AM


Properly time the cams and if it still has no compression take it to a shop & have a leak down test done.

  • Hamish

Posted June 04, 2005 - 02:25 PM


just what mac426 said.
After I did my gearbox, I reassembled my engine to have no compression also. I didnt disassemble the head, so it was still costed in carbon. I assume a bit of carbo came dislodged and was holding one of the valves open. I ran the bike for 5 minutes on a weak 2T bland and it was good as new :)

  • grayracer513

Posted June 04, 2005 - 03:14 PM


The manual is definately wrong....i've done loads of valves & stuff in my time

If you are using OEM Yamaha cams, the manual is absolutely correct. What do you think is wrong with it?

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