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help identifying a valve shim size...

Discussion in 'XJ Technical Chat' started by noah scott, Apr 21, 2022.

  1. noah scott

    noah scott Member

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    Got the ones that were out of spec documented... this one is fine, but i'd like to figure out what it is for when it DOES go out of spec, I can get it replaced.
    they're all MMs, so if it's a Y285 shim, it'd be 2.85 mm, right? so i can just take my calipers?

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  2. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    I would say that is pretty illegible.

    It's OK to leave it a mystery for now I think. As long as it is in spec it's fine. Knowing would be nice, but whattaya gonna do? Unless you have a micrometer laying around.
     
  3. Huntchuks

    Huntchuks Well-Known Member

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    Yes, shims need to be checked with a micrometer, not calipers. Calipers are not accurate enough.
     
  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Calipers are accurate enough, and have enough resolution, if the goal is to measure the original size. When new (and even when quite well used) the shims are the same thickness edge-to-edge. The only place that they can possibly wear is in the center where the cam lobe rides on the oil-film. A micrometer only measures at the relatively small contact patch of the pins. A Caliper measures along the relatively long edges of the caliper jaws, allowing for an edge-to-edge measurement of a shim.

    OP,
    Long story short; use calipers to measure the shim thickness. Shims are hardened and don't wear significantly. They get changed long before that can happen, because of valve seat recession which is why the shims need to be changed so the valve clearances can be adjusted back to specification.
     
    Timbox and hogfiddles like this.
  5. Huntchuks

    Huntchuks Well-Known Member

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    Considering the difference between a 190 shim and 170 shim (skipping 180) is still less than .001" and calipers only measure to .0005" depending on how much pressure you exert, I don't use calipers even though I have four sets.
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Micrometers are pressure sensitive too. User error is not reason to avoid using a particular tool.
    Also, why are you using SAE scaled calipers to read Metric parts?
     
  7. Huntchuks

    Huntchuks Well-Known Member

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    Just using inches as an example. My three digital calipers measure in SAE and Metric and my dial calipers only in SAE, of course. Mics are not nearly as pressure sensitive since they have the knob that spins after the correct pressure is applied. A much better measuring instrument even if you need to convert the measurement to metric. There is a reason calipers round to .0005" or .01 MM, before human error is introduced.
     
  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    There's nothing wrong with using wither calipers or a micrometer to measure shim thickenss.

    +/- .02 mm is accurate enough to do the job, especially since shims for our motorcycles are only made in 0.05 mm increments.
     
  9. Huntchuks

    Huntchuks Well-Known Member

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    Original shims were 0.01 mm increments. You can still have them made to .01 mm. I did for my X.
     
  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The airhead shim chart has increments of 0.05 mm listed. Yamaha and Len sell in 0.05 mm increments. Most of us have airheads.

    This discussion has gotten hopelessly pedantic.
     
  11. Huntchuks

    Huntchuks Well-Known Member

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    Pull original shims and see if they are all 0.05 mm increments. Measuring gaps with feeler gauges is sloppy itself, so I prefer to not add error by measuring shims accurately.
     

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