valve question: both exhaust are out by the same amount


4 replies to this topic
  • ams14

Posted February 19, 2012 - 03:57 PM

#1

Just checked the valves on my 06 yz450f. This is the first time I have done this. It's been about 30 hours since the last check (checked at shop by previous owner when a new timing chain was installed). Bike has about 200 hours on it, original valves, most (maybe all) have been shimmed in the past.

intake valves all look good, between 0.10 and 0.13 mm

Both exhaust valves seem to be around 0.15 or even a little less. Could something else (timing, etc) cause both valves to be out? Also, i could have messed up the measurement procedure, though it seems pretty straightforward.

thanks!

  • grayracer513

Posted February 19, 2012 - 06:58 PM

#2

Yes, timing can affect the reading, although it might affect the way the bike runs to a greater degree. Be sure you're at TDC and check the timing before you measure.

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  • ams14

Posted February 21, 2012 - 07:57 AM

#3

By 'check the timing' do you mean use the timing light or just make sure all the marks line up? The marks do line up, so one of the cams is definately not off by a link.

Also, when I am putting the cams back in and timing chain back on (with the tensioner removed), how do I know there is not slack in the chain on the forward side (non-tensioner side)? Do you just pull tight?

Do people ever mark the chain and cams with something to make sure they get the right spot back, and if so, what do they use to mark?

  • Dirk D

Posted February 22, 2012 - 11:04 AM

#4

Align the timing marks at tdc both cams will be facing opposits, punch mark on ex'st will be 9 oclock inl't at 3 oclock recheck then reshim back to specs............simmples so dont leave it too long tho...

  • grayracer513

Posted February 22, 2012 - 01:01 PM

#5

Also, when I am putting the cams back in and timing chain back on (with the tensioner removed), how do I know there is not slack in the chain on the forward side (non-tensioner side)? Do you just pull tight?

Yes. Roll the cam backward a little until the chain has no slack, then rotate the crank forward to realign the TDC mark if necessary.

Do people ever mark the chain and cams with something to make sure they get the right spot back, and if so, what do they use to mark?


Some mark the chain, but there's no way to be really certain that the chain won't move to a different position on the crank at some point, and if it does, then the marks on the chain would be wrong. A permanent felt marker works.

A useful trick to getting the second cam in the right place on the first try in a 450 is to first position the exhaust cam so that it's correctly timed and the slack is out of the front side run of chain. Then count 13 pins of chain from the mark at 12:00 o'clock on the exhaust cam and set the chain over the intake so that the mark that will sit at 12:00 on the intake is between the 13th and 14th pins. The cam will very likely roll into the correct spot on the first attempt this way, but ALWAYS double check the timing using the marks at 9:00 and 3:00, not those at 12:00.





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