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Thread: Flywheel runout tolerance question

  1. #1

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    Flywheel runout tolerance question

    Just put on my Quicktime bell housing back plate and re-installed the flywheel. I torqued it down in increments in a star pattern. I put on a caliper and rotated the disc and took measurements. The photo shows the highest difference to zero. I took measurements at different areas of the flywheel with the same or smaller amounts.

    Is 2 thousands an acceptable runout? If not, how can I fix it?


  2. #2
    Senior Member
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    I would think that you'll be just fine.

    Have you checked the bellhousing runout? This is usually more of a concern.

    Jim

  3. #3

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    Jim

    Thanks for the quick reply. The bell housing runout is the next step.

  4. #4
    Senior Member Fixit's Avatar
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    .002 runout on a disc 12" in diameter is just fine... well within acceptable.
    John D. - Minneapolis 'Burbs

    1965 El Camino - LT-1, 4L60e, 4wh discs, SC&C susp.
    2013 F-150 Platinum - Twin Turbo 3.5
    2018 Mk4 Roadster - #9365 Build Thread

  5. #5
    Seasoned Citizen NAZ's Avatar
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    Intuitively I believe a .002" axial runout of the flywheel even at the point you're measuring is not a problem but that .002" is going to look worse when you measure from the point we normally measure for flywheel axial TIR. And regardless of opinions on this forum, mine or others, you should always reference a service manual for the real spec. Flywheel axial runout is usually measured from just inside the pressure plate mounting holes unless a manufacturer states otherwise. And you did debur and clean the mating surfaces throughly before mounting the flywheel? It only takes a small dirt or rag particle to affect the TIR.

    Consider that a crank flange axial runout limit may be .002" - .003" and then look at the ratio between the centerline of the crank and where that measurement was taken and compare that to the point the flywheel axial TIR is normally taken. You can see that where you place the dial indicator on the flywheel is many times farther from the crank centerline than the TIR measuring point on the crank flange. Therefore, you would expect the axial runout of the flywheel to be much greater than the runout on the crank flange. An inspec TIR crank flange axial runout could cause a significant axial runout of the flywheel.

    Late Edit: I should have also mentioned that if you simply turn the crank without holding axial pressure on it you could be getting an error in your TIR reading. The crank thrust bearing clearance can show up as additive to your axial TIR.
    Last edited by NAZ; 09-22-2018 at 08:44 AM.

  6. #6

    Ol Skool

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    Both axial and radial runout need to be measured as far from center as possible on the machined surface. Then mark where the radial is greatest from baseline. This will help when you do the bellhousing runout. The bellhousing also needs to be measured on 2 separate planes for both the mounting face and the bearing housing. Sometimes the powder coating needs to be removed on a Quicktime, not always though. The T56 style can be a little challenging also. I think Tremec likes .005" or less, but look it up on the tremec site if that's your tranny.

  7. #7

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    Thanks for the detailed information. Im not a mechanic nor am i a weekend mechanic. This is all a new adventure for me. Any information is helpful. In terms of the photo and measurements, this photo is not accurate. I did get the .002 measurement just inside the clutch plate mounting holes and I staged the dial at that measurement and location to just take the picture to ask on the forum. ( hope that made sense). I found out That measurement is within tolerance. Now onto the bellhousing runout. It was just out of spec and i ordered a set of the smallest .007 offset dowels. Well see how that goes. Thanks again

  8. #8
    Seasoned Citizen NAZ's Avatar
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    Good to see you are doing it right. Most would skip this step either because they didn't know better or because they just assume it will be OK. When you pay attention to the details your build comes out so much better. No shame in having limited experience -- we all start somewhere. You can be proud that you are taking the time and extra steps to make it right.

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