CRF250X can't rotate engine after valve shim
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    kiprock
    Posts: 4
    Joined: Fri Mar 06, 2020 6:25 pm

    CRF250X can't rotate engine after valve shim

    by kiprock » Sun Feb 28, 2021 11:39 pm

    Hello! Looking for some help here.. I just adjusted my valve clearance on my 250X and after re-installing my timing sprocket and re-engaging the tensioner, I can only rotate the engine 1.5 times and the piston hits the exhaust valve when I manually rotate the engine. I can tell because I have a long rod sitting on the piston and as it comes near the top, the exhaust valve is being pushed down and I cannot rotate the engine past that point. I have taken the timing chain off the sprocket several times and made sure the piston was at TDC and the marks on the timing sprocket are parallel to the engine case. but the timing is clearly way off! Almost like the timing chain is catching on another gear or something. Any advice? Thanks in advance!!
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    JimDirt
    Posts: 4406
    Joined: Sat Nov 25, 2006 6:31 pm

    Re: CRF250X can't rotate engine after valve shim

    by JimDirt » Mon Mar 01, 2021 11:13 am

    Most likely the cam lobes are facing down and it is 180 out , the lobes should be facing the rear of the head with the lobes pointing at around 2 O'clock when the marks are aligned , that is the only way that the valve would hit if all marks are aligned ....

    The cam lobes need to be pointing in the direction shown in the pic below .. (note in the picture where it says "Valve Clearance Inspection" , there is some arrows with a (2) and (3) that is where the lobes should be facing , back by the rear tower bolts)

    Image
    2020 CRF450R
    2006 CRF450X
    Image
    Weiser , Idaho
  • User avatar
    kiprock
    Posts: 4
    Joined: Fri Mar 06, 2020 6:25 pm

    Re: CRF250X can't rotate engine after valve shim

    by kiprock » Mon Mar 01, 2021 12:04 pm

    Thanks for your reply @jimdirt
    The lobes are facing back towards intake as indicated in the diagram/photo.

    Could it be that the chain is not centered on the gear below?
  • User avatar
    JimDirt
    Posts: 4406
    Joined: Sat Nov 25, 2006 6:31 pm

    Re: CRF250X can't rotate engine after valve shim

    by JimDirt » Mon Mar 01, 2021 4:54 pm

    You should have the timing mark in the round plug (shown in the page from the manual I posted) , the cam lobes facing back , and the lines on the gear , and the line on the flywheel (the small round plug on the ignition side) all aligned at the same time , if all those marks are aligned it should be correct , and in no way would a valve hit the piston , which is why I am saying it must be 180 out or at least several teeth .... but no matter what ALL the marks have to match up

    Could the chain have moved on the flywheel , yes , but there should be a little bracket that keep the chain from falling down , unless it got bent by letting the chain have excessive slack and turning the crank , then the chain will bunch up down below and bend the tab , and then the chain can fall off the sprocket , the only way to confirm that , is to remove the ignition cover , and try to see the tab located on the right side of the gear , but you would most likely have to remove the flywheel to see it , you might be able to see it if you look from a lower vantage point , but no matter where the chain lands on the crank gear , if you align all the marks , it should be in time , , you can confirm the chain is on the gear by removing the cam , and pulling on the chain , and trying to turn the crank , if the chain turns it , then it is good , but the chain itself is not a timing marker , it is only a means to keep everything in time , so its relation to the crank gear is not relevant as long as it is on it , if it is not on the gear then either the chain will be too loose , or you won't be able to get the chain on the cam sprocket because it will be too tight ..... so something is going on with one or more of the marks having to be off to get the results you are getting

    What I would do is start over ..... first align the dot/triangle on the clutch side , when those marks line up , then look at the small plug and look for the line for the flywheel , if that is in line , then align the cam lobes back and the gear marks level , and you should be good ..... you are doing this with the timing chain tensioner removed completely , then once all are aligned , install the tensioner and check the marks again , if all are good , then crank the engine over by hand with the kickstart and turn it several turns , nothing should hit , then set the cam lobes to the rear , and recheck all the marks , if all are still aligned , then button it all up and you should be good to go ....
    2020 CRF450R
    2006 CRF450X
    Image
    Weiser , Idaho

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