Honda XR600R valve timing question

Discussion in 'Thumpers' started by WantToRideMoar, Jul 6, 2013.

  1. WantToRideMoar

    WantToRideMoar Been here awhile

    Joined:
    Apr 12, 2012
    Oddometer:
    337
    Location:
    Mesa, AZ
    I've got the Clymer manual for my new-to-me 1993 XR600R sitting here in front of me, and a task for myself after experiencing some hiccuping power while on the highway this morning.

    I'd get intermittent failure of the bike to deliver power on a combustion stroke, at 5500 RPM and higher. This resulted in some stuttery cruising on the highway on the way to a ride this morning.

    I've owned this bike for a little over a year and I've so far focused my maintenance tasks on tires, oil changes and a speedometer install. Never been into the engine itself thus far.

    I can find TDC by inserting a chopstick through the sparkplug hole and watching it rise/fall as I cycle the piston from the left side of the motor. I see the intake valves rise during one cycle and the exhaust valves rise on the second cycle.

    My Clymer manual says:

    I've rotated the engine probably 7200 degrees so far, and the rockers have no free play. Unless I don't know what "free play" means.

    What is meant by "free play" in the rockers? Them sumbiyatches are tight and have no rattle to them at all.
    #1
  2. whisperquiet

    whisperquiet Long timer

    Joined:
    Aug 24, 2007
    Oddometer:
    1,200
    Location:
    62298 in lovely corrupt/bankrupt Southern Illinois
    If the rockers have any free play at all (at TDC), you can feel movement as the rocker should have at least some clearance between the valve stem, the rocker arm, and the camshaft on which it rides. Here is a good tutorial on this:

    http://www.4strokes.com/tech/honda/setvalve.asp

    Your valve clearances may have closed completely up and have no "free play".
    #2
  3. CycleDoc59

    CycleDoc59 Wrench Rider

    Joined:
    May 24, 2006
    Oddometer:
    984
    Location:
    East Virginia
    The manual means that on one cycle, TDC occurs
    at "overlap", where the intake is closing while the
    exhaust opens. This is not where the valves can
    be checked. On the next cycle (engine rotated another
    180 degrees), TDC occurs at the top of the compression stroke,
    so both valves are closed. (air shoots out of the plug hole
    during this stroke, making it fairly obvious)

    At this point there should be a bit of play at each
    valve rocker, and where valve clearance is checked
    and adjusted if necessary.... If there is no free play
    at all, the valves cannot fully seat resulting in loss
    of compression, plus dirty and/or burned valves and seats.
    #3
  4. WantToRideMoar

    WantToRideMoar Been here awhile

    Joined:
    Apr 12, 2012
    Oddometer:
    337
    Location:
    Mesa, AZ
    K, now I'm confused.

    Linked article says:

    I have no freaking idea how anyone is supposed to rotate the engine with the kickstarter and micro-manage lining up the T-mark through the sighthole on the opposite side of the bike... Why would you write a how-to as weird as that rather than using something simple like a freaking wrench so you can sight the T-mark? What am I missing? Seems you don't have any business adjusting valve clearance if you don't have a socket wrench.



    And there is no rotating slowly... something is springloaded in there to force the thing to cycle hard through TDC after a certain point. I can't freeze it at the T-mark.


    I'm going to give it another try tomorrow morning... there was no play in my rocker arms at either of the TDC positions so I may have messed up and timed on the exhaust stroke. I don't know, it was 100+ degrees out today while I was doing this and I drank about a gallon of water while working.

    Just to be sure I understand...

    1. Pick the TDC stroke where the intake valves have opened and the compression stroke has happened, not the TDC stroke where the exhaust has just happened and the intake is about to.
    2. Try to center perfectly on the T-mark. Somehow. Even if the bike won't let me.


    However, CycleDoc, you said:

    Doesn't it need to rotate 360*, not 180? The T-mark should always be an indicator of TDC? Can the T-mark drift off TDC and need to be recalibrated?

    And.... assuming I did do everything right today (too hot right now and second guessing myself), would valves with insufficient clearance cause the skipped combustions I was experiencing on the highway at 5500 RPM?
    #4
  5. mcma111

    mcma111 Long timer

    Joined:
    Jul 17, 2007
    Oddometer:
    14,860
    Location:
    San Francisco,Ca.
    Did you get my PM?
    #5
  6. WantToRideMoar

    WantToRideMoar Been here awhile

    Joined:
    Apr 12, 2012
    Oddometer:
    337
    Location:
    Mesa, AZ
    mcma111, thanks for your advice and conversation yesterday. Really appreciated.

    All done with the valve clearancing now. Going to take it out in a little bit here to ensure the problem is resolved, run up and down the highway a bit to see if the stutter is gone.
    #6