07 250r. Having hard time shimming
  • Tm85cc07
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    07 250r. Having hard time shimming

    by Tm85cc07 » Thu Apr 28, 2016 7:24 pm

    I am new to four strokes. Just put a new head on and finding it hard to shin valves. When my engines is tdc I noticed the exhaust cam lobe is right on the small decompression lever in the cam. Is this right? Do you make your clearance while rocker is touching this mechanism? I also notice a very quiet click noise from this mechanism once the engine is turned to tdc. Any help is appreciated I must have tried shimming this head 20+ times and no luck
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    JimDirt
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    by JimDirt » Thu Apr 28, 2016 9:41 pm

    Welcome to the site !! \:D/

    Looking from the left side where the cam sprocket is , the slash marks (they look like this - -,one on each side of the sprocket) , need to be level with the head , the cam lobes need to be at the 2 O'clock position facing the rear of the engine

    Make sure that you have ALL 3 timing marks aligned , the left side small round plug in Timing Cover , , the slash marks on the cam sprocket , and on the clutch side the large round plug for the counter balancer marks , along with the cam facing 2 O'clock and you should be good , also make sure when you check the valve lash that the tower bolts are torqued to spec , otherwise the gap will be off

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    Weiser , Idaho
  • Tm85cc07
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    by Tm85cc07 » Fri Apr 29, 2016 3:29 am

    Thanks.... I do have the timing right. What I am unsure of is... At tdc, the exhaust rocker roller rests on the decompression lever after making a click noise. Do I need to check the backlash at this point? When all timing is aligned seems to be right on decompression lever.

    I ask this because once the rocker moves off of decompression lever backlash is much more.
    Thanks
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    JimDirt
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    by JimDirt » Fri Apr 29, 2016 7:50 am

    There is not a adjustment for the De-compressor ,(its a Auto-De-Compressor on that model) so no need to worry about clearance , the only clearance is for the Intake and Exhaust
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    Weiser , Idaho
  • Tm85cc07
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    by Tm85cc07 » Fri Apr 29, 2016 8:00 am

    Right. I understand that there is not adjustment for decompressor. However my question is.... When all timing marks are align, exhaust rocker is on auto decompressor. Therefore when it rolls off decompressor, backlash is much more.. Do I need to turn bike over so it is off of decompressor?
    Thanks
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    JimDirt
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    by JimDirt » Fri Apr 29, 2016 9:03 am

    As long as you are on the COMPRESSION stroke and the cam lobes are facing 2 O'clock (towards rear of engine) , then when all the marks are aligned there should be slight clearance on the rocker arm , if there is any clearance , so the rocker arm is NOT pushing the valve open which would indicate you are on the EXHAUST stroke then that is when you check clearance

    In other words you should be able to take hold of the rocker and wiggle it , it should not be tight enough to cause constant pressure on the valve stem when all the timing marks are aligned , so if the De-compressor is holding the rocker down on the valve stem , then something (timing , valve wear/shim size) is off , if the valve is excessively worn (usually the Exhaust valves don't wear as fast as the Intakes) , it will make the stem stick up farther which would lessen the clearance , which would necessitate a smaller shim ...

    But when everything is correct , there should be clearance from the rocker to the valve stem , and that is your only concern , if its not holding the rocker tight to the valve stem , then you should have clearance and should be able to get your desired measurement

    Make sense ??
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  • Tm85cc07
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    by Tm85cc07 » Fri Apr 29, 2016 9:10 am

    Yes. Totally understand all of that. I guess I am not making myself clear as to what my question is... Can we chat on the phone?
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    by Tm85cc07 » Fri Apr 29, 2016 9:43 am

    I have 50/50 raito of people telling me I have to adjust my valves when rocker is on auto decompressor lever ( when all timing marks are align) and the other people are telling me to turn engine so rocker is not on decompressor but rather the lobe
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    JimDirt
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    by JimDirt » Fri Apr 29, 2016 10:12 am

    Its not weather the rocker is on it or not , its the fact that the timing marks are aligned and there is a gap of some kind from the valve stem(where the shim is) to the rocker arm , the gap is determined by Valve Wear , and correct Timing Alignment , nothing else , the ONLY things that can alter the gap is Valve Wear or Timing Marks

    If the marks are aligned and you have no gap then the valve must be wearing and the shim needs to be replaced with a smaller one , and/or the valves need replacing and the seats cut , remember i said "as the valve wears" ?? , the valve face where it meets the valve Seat is what wears , it is the ONLY "wear item" in the valve train (with the exception of the valve seat itself and the Timing Chain) , as it wears the valve face becomes thinner , as it becomes thinner the valve Stem will stick up farther due to the wear of the face , which decreases the gap between the rocker and the shim/valve stem , which is why you have to adjust the valves in the first place

    As long as the tower is properly torqued down when checking clearance , then the ONLY movement of parts (due to wear) can be from the Valve Itself ,as the valve wears and the clearance is gone , then the valve sticking up farther pushes the rocker closer to the De-compressor which can not move as it is attached to the cam that can not move , so to simplify , if the valve wears it decreases the gap , the gap is determined by the timing marks being aligned and the proper shim size being on the valve stem and the amount of wear on the valve itself , which determines the size of the shim needed to keep the recommended gap , nothing else can change those settings

    The cam is stationary in the tower , it cant change the gaps , the rocker itself is stationary in the tower , it cant change the gap , the only "wear item" is the valve itself ( and the valve seat to some extent) , so the valve is the ONLY item (as long as the timing is correct and ALL marks are aligned when measuring)that can alter the gap , the De-compressor pin is retained within the cam , it can't make the gap tighter

    So no matter what , the gap is determined by the shim size , so basically if you have pressure on the rocker to allow it to touch the De-compressor pin , then it would mean the valve is wearing (or your timing marks are not aligned when checking clearance) and will need to have a smaller shim to correct the issue , or you are in need of a valve job , that's all it can be , the stationary parts have no relevance in the gap , only the valves wear does

    Did not mean to confuse you with my prior replies , hope that answered your question
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    Weiser , Idaho
  • Tm85cc07
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    by Tm85cc07 » Fri Apr 29, 2016 10:23 am

    I appreciate all of our input... Just spoke with someone who said to allow rocker to "click" past the decompressor and make adjustments then...

    I know the valves are good because I just paid $600 to have it redone. Now trying to shim new head

    When my timing aligns, rocker is on decompressor, there is clearance but when the decompressor opens then there is much more clearance
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    JimDirt
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    by JimDirt » Fri Apr 29, 2016 10:36 am

    I don't know how i missed the part about the "new" head , my bad , i am assuming you are using the "old" shim and that is why your having a issue with the clearance , but as long as the marks on the gear are aligned as i mentioned , then the gap should be able to be checked properly , if the sprocket marks are aligned then the De-compressor should not be touching the rocker (as long as the correct shim is installed) , the clearance AFTER the timing marks are aligned (once it moves in rotation) is irrelevant , all your concerned with is TDC , as this allows the valves to remain closed for compression , so when the gap increases because of the movement , its not a factor in the gap
    2020 CRF450R
    2006 CRF450X
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    Weiser , Idaho
  • Tm85cc07
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    by Tm85cc07 » Fri Apr 29, 2016 4:29 pm

    Thanks for the help I will let you know how it goes!
  • Tm85cc07
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    by Tm85cc07 » Thu May 05, 2016 5:21 pm

    When I shim my exhaust valves to proper clearance....turning engine over by hand and it stops.
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    JimDirt
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    by JimDirt » Thu May 05, 2016 6:21 pm

    it locks up ??

    If so , it has to be a timing issue , either timing chain slipped/worn , or tensioner is bad and sticking out and locking the chain
    2020 CRF450R
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    Weiser , Idaho
  • Tm85cc07
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    by Tm85cc07 » Thu May 05, 2016 6:25 pm

    New cam chain and tensioner. Is it possible the cam gear slipped? This bike blew on me in semi high rev. All my timing marks are spot on.

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