Dial Indicator Reading Help Please

Discussion in 'The Garage' started by scootertrog, Apr 13, 2013.

  1. aftCG

    aftCG Been here awhile

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    Also wrong adding in the 1 from the small dial because it isn't past it yet. The OP either rotated to zero with quite a bit of preload or the indicator is junk, as you'd expect that needle position from around .9 on the main dial, not just past zero. Either way, it's only total indicated runout that we're intereste in here.

    I concur, it .0055"

    Also, setting zero at the lowest point is valid because you're measuring total indicated run out that way. Setting it at a medium "datum" would still give the same numbers (assuming you zeroed with some preload and watched for the negative values), but what you did is spot on.
    #21
  2. Beezer

    Beezer Long timer

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    if we're gonna pick fly shit out of the pepper it's prolly .0056 :rofl

    and if you got .013 on the other it's out. question is.... is it a thickness issue? (doubt it), bent rotor... mebby, or can the rotor be shimmed true

    has the rotor been off? if so maybe a removal & cleaning of the hard points will get you back in limits

    put it on a plate of glass & see if it's bent
    #22
  3. scootertrog

    scootertrog Been here awhile

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    Thickness is about .4mm, well within spec. Rotor has not been off, it is about 4-1/2 years old. The rotor pad area has been scotch-brited and cleaned, and the bobbins rotated freely and cleaned. The rotor carrier bolts are really tight, but at this point it wouldn't hurt to take the rotor off and check it on a plate - seems I've done just about everything else anyway, lol.

    Just to be clear, I set the dial travel about 1/2 way into it's range before contacting the rotor, then rotated the dial face to zero when the lowest spot on the rotor was found, thus the measurement you see in the photo is total runout.

    Thanks everyone for your input! :clap
    #23
  4. LuciferMutt

    LuciferMutt Rides slow bike slow

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    What in the fuck are you talking about?

    EDIT: Nevermind...
    #24
  5. troidus

    troidus Long timer

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    4mm I could believe, but .4 sounds a little thin.
    #25
  6. scootertrog

    scootertrog Been here awhile

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    Yep, you're right, my screw-up there, lol. All these ......... and mmmmmmms get to me after awhile. :D
    #26
  7. lnewqban

    lnewqban Ninjetter

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    I would make more than one measurement (radius-wise) and also would estimate the difference between extreme deflections rather than setting the dial to zero.

    Your hand can introduce an error in the support while twisting the marker to zero.

    Your measurement is above the limit only 0.030 mm, which is nothing.
    I believe your pulsations are not due to that but to bad disc surface, bad pads, frozen parts, etc.

    Use a micrometer to determine the rotor parallelism and to measure rotor thickness.
    If the rotor thickness is below the minimum thickness, it must be replaced.

    Ten rotations of your dial are one inch.

    Dial's specs:


    <table class="data-table" id="product-attribute-specs-table"><tbody><tr class="even"><th class="label">Graduations</th> <td class="data last">0.001 in.</td> </tr> <tr class="odd"> <th class="label">Indicator type</th> <td class="data last">Dial</td> </tr> <tr class="even"> <th class="label">Range per revolution (in.)</th> <td class="data last">0.1 in.</td> </tr> <tr class="odd"> <th class="label">Resolution (in.)</th> <td class="data last">1 in.</td></tr></tbody></table>
    #27
  8. scootertrog

    scootertrog Been here awhile

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    The indicator set-up was a clamp-on type, the clamp was attached to the bottom caliper rib and seemed to be pretty steady. I know things need to be steady here, so I tried my best. I am confident that I got a good measurement.

    That's what I thought too, but pads were new-ish, removed and sanded with 200-grit to exposed fresh meat. Carefully re-bedded per Galfer's instructions. Disc is clean enough to eat off, lol. Brake calipers were completely taken apart and cleaned as well. Did a complete re-bleed of fluid. Also double-checked the fork mounting heights to make sure they were equally above the top clamp. The ONLY suspect anomaly I have found thus far is the run-out measurement.

    Thickness is very close to original spec and still good. I've got a replacement set of rotors on order, I'll update this thread on the results of installing them.
    #28
  9. Beezer

    Beezer Long timer

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    rotor bolts are probably in with a thread locker so some heat is in order.... also an impact if you can lay hands in one
    #29
  10. H96669

    H96669 A proud pragmatist.

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    Yes to the micrometer. I did one like that a couple years ago, sure found it uneven in thickness. Caliper readings were "in specs" but they average over an inch or so.The micrometer way is much better.
    #30
  11. GH41

    GH41 Been here awhile

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    I wouldn't trust the HF anything to be accurate!!!! GH
    #31
  12. Motomantra

    Motomantra Registered Lurker

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    Rotor run out reading with a dial indicator may be inconclusive due to the rotor designed to float on the buttons.
    Try taking a plastic hammer to the high side of the rotor to see if it shifts. Tap, tap lightly so as not to create any more damage.
    #32
  13. slidewayes

    slidewayes slidewayes

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    +1
    #33
  14. MCMXCIVRS

    MCMXCIVRS Long timer

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    The correct measure as some have stated is ~0.0055" (the tenthousanths is a best guess using that dial indicator).

    However, rotor runout is unlikely to cause pulsation on its own. Runout may cause the brake lever to have too much travel on initial application as the wavy rotor pushes the pad further back leaving excess clearance that must be taken up when the brakes are applied. If you are sensing pulsing, then the problem is thickness variation (also refered to as parrallellism) at various points around the circumference of the rotor. While a fairly large amount of runout can be tolerated (as indicated by the specs), very little thickness variation is acceptable, usually less than 0.002" - 0.003". The variatins in the rotoir thickness cause the pads (and thus the brake lever) to move in and out to follow the rotor.

    Use a micrometer (calipers will not work very well for this as they cannot measure a small enough area on the rotor faces) to measure the thickness of the rotors at multiple points to determine if they are all the same or very close in thickness. Also, look for obvious high spots that might indicate hard spots on the rotor caused by overheating.
    #34
  15. scootertrog

    scootertrog Been here awhile

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    Update - Received replacement rotors and problem solved. :)
    #35