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YZ250F Timing Help

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So I'm checking the valves on my 2009 YZ250F today. Everything was going smoothly until I went to set everything at TDC. I lined up the dots on the cam sprockets level with the head and made sure the cams were pointing out. I then checked it through the timing access hole in the ignition cover. But, I couldn't see the timing mark - it wasn't properly lined up. It was slightly ahead of where it should be. So when I lined the timing mark back up, the dots on the cam sprockets weren't level with the head, and the cams weren't pointing out quite right.

So does this mean my timing is off? This may also be why the bike was running so poorly when I got it, backfiring and sputtering. Any help would be appreciated!

These shots are with the dots lined up, but the timing mark not visible.

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Alright, thanks. This is new to me, so how would I go about re-setting the timing? Is a timing light needed? I will read up on it in the manual as well.

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No timing light

Remove the spark plug

Remove the cam chain tensioner per the manual.

Get the crank at TDC per the marks.

Move the chain on the cam sprockets to get them to line up

Re-install the tensioner

Rotate the engine slowly and carefully two revolutions (will be one revolution of the cames) and re-check the cam timing with the engine at TDC Do it again if you want to be 110% sure (I always do).

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I cannot get the 3 dots to line up with the head now when the crank is at TDC. One always seems to be slightly out of line. Does this mean my cam chain is stretched? The bike has around 25 hours...

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I have it mostly torn down right now so I can't start really start it, besides I would be a little nervous to right now. But before winter it ran like crap with no power and wouldn't even idle. I have the carb off right now and am giving it a good cleaning, but now seeing how the timing was off, I believe this is the real cause of my problems.

Anyway, before I took off the cam chain tensioner, the dots all llined up perfectly. After moving the cam chain around on the camshaft sprockets, I thought I had it right. I've fiddled with it for nearly an hour, but they simply won't line up, which has lead me to the conclusion that the cam chain has stretched.

Also, when turning the crank with the wrench (counterclockwise), the resistance slowly builds up then realeases abruptly, spinning the socket back clockwise a bit. Is this normal?

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Quote "Anyway, before I took off the cam chain tensioner, the dots all llined up perfectly"

Haven't you answered your own problem?

"they simply won't line up, which has lead me to the conclusion that the cam chain has stretched"

There is no way a cam chain will have stretched after 25 hours of use

"the resistance slowly builds up then realeases abruptly, spinning the socket back clockwise a bit. Is this normal? "

YES !! when turning it you are making the cam lobes press down against the valve springs and then when they go over the highest point of the cam they find it easier to speed up the rotation, this is easily combatted by 'not' using a ratchet and by using a 'T' bar to control to action.

Start again:busted:

Put the crank at TDC on compression stroke WITH the CCT installed then check the dots on the camshaft are lined up (they may not be exact but should be within 1/2 tooth). If it is a full tooth/link out of place it might have slipped a tooth and that would point to a weak CCT which would need replacing (there will be a 'manual' CCT on the market somewhere which would be better)

Then go and sort out the fuel problems, if the bike has been stood around a lot the minute holes in the jets may be 'clogged' up? For the cost of a new set of jets it may be better changing them. Also try changing the plug and cap as these are cheap and its good to eliminate things starting with the cheapest first.

Ian Scotson (scotty)

8 years ago my son raced a YZF250 in the UK :excuseme: and thats the reason for my forum name:thumbsup:

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You are never going to get the marks to align perfectly.

Turn the engine back a few degrees before TDC. Now rotate both camshafts back, so that all the slack is out of the front side of the chain. Using a rod or your finger to keep pressure against the rear guide through the tensioner hole, turn the engine forward to TDC. Now check your marks.

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Align the crank to the proper marks. Before you do the next steps you need a torque wrench for the cam cap bolts. Take the tension off of the timing chain remove the caps off of the exhaust, and intake cams, remove the intake cam 1st while taking the timing chain off by rolling the intake cam towards the front of the motor till you have enough slack in the chain to remove the cam. Next remove the exhaust cam and chain. Now reinstall the exhaust cam back in place in the proper position with the timing chain, there should be no slack on the portion of chain that runs to the crank on the front of the motor. This will be a trial and error method till you get the chain tight and the exhaust cam in the proper position. When that is done count 12 pins on the timing chain from the top dot on the exhaust cam sprocket, mark that 12th pin with white out. Now install the intake cam that white doted pin should end up on the top dot on the intake cam. Verify everything with photos in your manual. Install the cam caps torque to 10 nm this is very important. release the cam tensioner and everything should be correct. Rotate the crank with a wrench several times to verify everything is correct.

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You should be turning the crank counter-clockwise. This is the normal rotation of engine, and it will put the slack in the chain on the tensioner side. You can take up slack with your finger thru the tensioner hole ans the marks will be on.

Al least that are for my bikes.

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Alright guys, well I went ahead and decided to replace my cam chain. I got to the stator and removed it, and found a nice surprise on the back:

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The mark is a couple mm deep, and obviously caused by the cam chain. I don't think this would affect anything though, would it? Just another reason for me to replace the chain.

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