Before I do something I regret...

Discussion in 'Airheads' started by 2GbeemerLUV, May 18, 2012.

  1. 2GbeemerLUV

    2GbeemerLUV Bavarian Motor Pie

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    Trying to gain a fuller appreciation for my machine and how it works, I popped off a valve cover to try and see what that adjustment looks like. Following my clymers, I found tdc on the compression stroke and took measurements: 0.01 intake and 0.02 exhaust. Perfect as expected- this machine was resurrected only but a year ago, more accurately, less than 1k miles ago.
    Upon further inspection, where the measurements were right, the OT mark on the flywheel was about 1.5 cm north of the middle of the window. "hmmm, ok, advance the flywheel so OT is dead center and remeasure" in this position, there is no free space at all, everything is pressed tight.
    What are the indications?
    Should the adjustments be redone with OT centered or is it within a tolerance?
    Does this tell me the timings off?
    Am I crazy? Am I making any sense?
    #1
  2. ignatz72

    ignatz72 call me iggy

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    Sounds like the bike was timed for full advance rather than static/idle. I had to do the same for my GS so that it would run correctly.

    But I set my valves according to centered TDC mark, not adjusted for the altered timing.

    Others may chime in differently but my bike is happy according to plug readings and performance.

    *EDIT* Never mind, AW and HG picked up on the issue better than I did.
    #2
  3. Airhead Wrangler

    Airhead Wrangler Long timer

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    Try turning it over 360 degrees to the "next" OT mark. Then see if they're still tight.
    #3
  4. hardwaregrrl

    hardwaregrrl ignore list

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    Check your pushrods at TDC and see if they turn. That's an easy way to figure out which side is ready to be checked.
    #4
  5. 2GbeemerLUV

    2GbeemerLUV Bavarian Motor Pie

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    Are you saying I may have the opposite cylinder on compression instead of the one I'm "adjusting"? So 360 from where I'm at and check for free spinning pushrods? Aka: pushrods will only spin on comp stroke for that particular cylinder?
    #5
  6. ozmoses

    ozmoses Ride On

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    Yes, that is what they mean.

    Also, I(we) asume your given measures are .10/.20 mm?

    otherwise- .004/.008.
    #6
  7. disston

    disston ShadeTreeExpert

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    The pistons are traveling in and out together. Have both valve covers off. Turn engine over and the side that the intake valve has just closed on is the side you adjust when it reaches OT. Turn another 360* and adjust the other side.

    Ozmoses is right. The figures you gave are incorrect. Try not to make this kind of mistake. It can lead to regrettable expense.
    #7
  8. 2GbeemerLUV

    2GbeemerLUV Bavarian Motor Pie

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    Sorry, typo. Correction: 0.1/0.2mm was measured- thank you. (noob)

    Also, "opening" is when the intake valve is travelIng into the cylinder, right? So "just closed" is when the intake valve appears the longest? (noob)
    #8
  9. zenduddhist

    zenduddhist Been here awhile

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    I believe it's the opposite. When the intake valve is travelling away from the cylinder it is open. As it closes, it will be moving towards the cylinder...

    Someone verify?
    #9
  10. disston

    disston ShadeTreeExpert

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    The valves are normally closed until the cam shaft acts on the valve train and opens any of them. When a valve is closed on a solid lifter , not a hydraulic lifter machine, there is valve lash. This is the space we measure with a feeler gauge between the tip of the valve and the tip of the rocker. The valve is closed when it will not flow and the valve face is on the valve seat. When the valve is open it will allow flow of gas and or liquid. When a valve is open there is no lash, a feeler gauge can not be put between the rocker and the tip of the valve, the valve spring is compressed.

    On the 4 stroke engine there are two Top Dead Centers per combustion cycle. Only the one at the end of the compression stroke has both valves closed and both can be set. The intake valve will open with the movement of the intake rocker on the intake stroke, the piston is traveling down and the valve opens to let gas in. Just before the piston starts back up the intake valve closes, The intake valve should be entirely closed on the compression stroke and the exhaust will not open till the end of the power stroke so both valves are closed for most of 2 of the total of 4 strokes of the engine. That is they are closed for half of the time. It actual practice there is a lot of overlap and the valves take time to make all this motion but for the purpose of setting the valves use TDC after the intake valve has closed.

    This is assuming that you are turning the engine in the direction it normally travels during operation. Looking at the front of the engine with the cover off the engine should turn clockwise.
    #10
  11. disston

    disston ShadeTreeExpert

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    The comment about the valve being closed when the valve is longest was correct, I think. The Buddist guy was wrong.
    #11
  12. ozmoses

    ozmoses Ride On

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    Think of the valve as, well, a valve or perhaps a door. Open is open, closed is closed.

    Opens into combustion chamber. Closes at (in) the head.

    Take a length of coat hanger, or stiff wire & insert into the spark plug hole; as the piston rise in the bore it will push the wire ahead of it. When it stops pushing, this is TDC for that particular cylinder.
    #12
  13. bmwloco

    bmwloco Long timer

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    TDC

    .6 intake, .8 exhaust.

    Rotate and repeat.

    Thusfar, it has worked for this monkey. YMMV.
    #13
  14. ozmoses

    ozmoses Ride On

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    Fixt, as they say. No offense, I just want the OP to have apples to apples.

    We know what you mean.:deal

    So, OP- what's the deal? Nice day to ride...
    #14
  15. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    But it HAS to be TDC on the compression stroke, NOT on the exhaust stroke. Any ole TDC won't work...
    #15
  16. 2GbeemerLUV

    2GbeemerLUV Bavarian Motor Pie

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    great stuff folks, and its all making sense- THANK YOU!!

    just woke up, tuned my own valves last night.

    ozmoses, i think i will in fact, violate my cylinder with a coat hanger, then take a ride on this perfect day.
    #16