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Yz250f timing off. Help

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Tore bike down to check valve clearances, bike runs great. When I check with a feelers gauge I can't fit the

.10mm gauge in, the biggest I can get is the .04mm and I can't seem to get my timing marks "I" and the marks on the cam sprocket to line up correctly am I doing something wrong pls help. Timing mark on flywheel "I" set at TDC and piston is all the way up. Marks on both the cam sprockets are pitched towards the back of the bike.Any help would be appreciated.

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Are you on the third "line" on the flywheel?  Looks like the cams are off 1 tooth.

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I'm on the "i" line right after the "h". I'm confused cause if they were off 1 tooth it should run like garbage but it runs great besides some small issues when restarting the bike while its hot but that's a different issue for another day lol

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ok, you may have some timing chain wear then.  I think I would advance so the cam marks line up as they should and then check lash otherwise time to shim the valves.

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My original goal was to check the valve lash but can't find tdc to be 100% sure of clearance from where I'm at now the exhaust is at .18mm and the intake is .04mm. If that's correct then exhaust is ok but intake is
.06mm too tight

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yes, exhaust is good, but intake is off.  Try advancing until cam marks are correct and recheck lash.  Chain is either worn or timing off 1 based on the picture (which may be deceiving my eyes).  I just checked a friend's bike and the outside intakes were fine but the inner was at .05mm which required a new shim.  Bike pretty much ran fine except for slight difficulty on cold start.

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Would the bike still run good if the cam were each off by 1 tooth? And no your eyes are not deceiving you marks are off by 1 tooth but I didn't know if it was an error on my part or something fishy in the motor

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The flywheel can spin on the crank if the woodruff key is missing, worn, or broken.  Does the chain feel tight?  Can you pull take tension off of the tensioner and see if it is at its limit?  The timing chain is cheap - like $20.  Maybe cheap insurance to replace.  Tensioner is more expensive, around $60 from memory.  You would also need a flywheel puller.  I still would advance slightly where cams are at proper location and see what lash is at.  I'm thinking you will still see them out of spec.  If you have to pull the cams to re-shim then I would change chain too.

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Chain feels tight tensioner also feels tight and I don't think it's a missing or broken flywheel key but it never hurts to check. I'll try advancing the cams and re checking the lash and if they need to be re shimmed I will take your advice on the chain but I'm still confused on how it would run while being 1 tooth off timing I feel like I'm doing something wrong. Anyways thank you for your input I really appreciate it, I will let you know what the verdict is when I figure it out

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With the tensioner you want to make sure it is not fully extended.  If it is then you know the chain is at its limit.  Pull tensioner and count the number of rotations it takes to fully retract.  Then re-install (you have to use screw driver to hold rod out.)  Slowly count the number of rotations you allow the rod to extract before it stops.  If you are at the number you counted then you know it is at its full extracted position.  There is also a maintenance procedure described in the manual where you ensure it has smooth operation, etc.

As for being off one tooth and still running - I would assume there is slight tolerance to timing.  Bike may not be running as well as it can.

 

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I'd be impressed if it runs better it has given me no issues and I've run it through it's paces. Raced a 400ex awhile ago and got him by about 3 lengths which impressed me but then again it all comes down to the rider in my opinion. I will keep you updated and thanks again for your help

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It will run one tooth off on the intake... but not the greatest and will back fire...

where do you find a timing chain for $20.00???

cheapest timing chain I can find is $60-$70..,

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It runs good only issue is it's hard to start if it stalls when it's hot. When the bike is at TDC off the flywheel the cam sprockets do not line up with the head surface they are 1 tooth off it seems but the bike runs great? Is this even possible

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1 hour ago, Yakattack said:

It will run one tooth off on the intake... but not the greatest and will back fire...

where do you find a timing chain for $20.00???

cheapest timing chain I can find is $60-$70..,

Partzilla.com and there are probably cheaper sources for my 04 yz250f

 

TimingChain.PNG

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You guys are playing with a loaded gun.  Keep on playing around and your gonna have a major motor catastrophy.   Correct the problem!

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