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Thread: DKM Twin Disc Flywheel bolts backed out - Any thoughts?

  1. #1
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    DKM Twin Disc Flywheel bolts backed out - Any thoughts?

    My recent turbo setup had a pretty tough failure with a DKM twin disc clutch (DKM MS-006-005) and flywheel after about 500 miles. Red locktite used on bolts and torqued to 105NM / 77.5ft-lbs. Stock harmonic balancer. Do you guys have any ideas? Luckily, only the flywheel/pressure plate is trashed and not the crank.

    Car made 643whp/599torques. Never drag raced, never launched, no slicks. I'm now trying to deal with a shop and clutch company who both don't want to be shouldering any responsibility for this. Has this happened to anyone else? What might have caused this? I have installation failure, bolt stretch, and clutch imbalance as potential causes. Is there anything else? What is most likely?

    Bill

    knestrick flywheel.jpgknestrick disc.jpg
    Last edited by wgknestrick; 01-05-2021 at 08:56 PM.

  2. #2
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    Was there any early warning signs.? Vibrations or something else? I ask because I installed the same clutch in my car.

    Sent from my VS995 using Tapatalk

  3. #3
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    Absolutely,
    I was getting a "RRRRR" sound after every clutch in or whenever the engine got off load. I took it back to the shop twice for this noise and they originally thought it was a Vanos rattle from the VAC cams. Shop kept claiming it was a normal sound that M50s can make when cammed. Rarely, it made a horrible rattling at idle, but only made this sound like twice and then stopped. This being my first twin disc, I had a hard time discerning what sounds are considered "normal" and what are concerning. Twin discs have been reported to be slightly noisier than singles and just thought this was "normal".

    The sound was very hard to isolate where it was coming from as you couldn't hear it very well without driving it / loading the car up. Car eventually failed on normal stop/go driving and I couldn't shift into gears. Clutch wouldn't disengage either.

  4. #4
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    77.5 ft lbs = 105 Nm... I assume 1065 is a typo. Threadlocker fails around 450 degrees F. It's not impossible that putting that much power through a twin disc could have gotten the flywheel that hot. I would install new parts with new, clean and dry bolts and make sure the torque wrench is calibrated if it's a clicker type.

    Sent from my LM-V350 using Tapatalk

  5. #5
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    I’m also a bit surprised red failed too, but if the crank went over 450 I’m sure it would be discolored from that. I’m more inclined to think there was oil on the threads and/or they were not properly torqued.

    Just because bolts are new does not mean they are clean. Acetone wash the threads as well as the threads in the crank. I use a plastic lab bottle with a squirt nozzle on it. Wash and blow out with air a few times. Be liberal with the locktite and give it time to set up.

    You may also consider a higher grade bolt. Again, just because it’s new does not mean it’s good. I’m guessing those are 10.3 grade (similar to grade 8 sae); there is a sae grade 12 that is 14. Something I think in metric. Go someplace like McMaster-Carr and get high grade bolts. Heck spend the slight up charge and get MIL spec if you can, or a specialist like ARP. Another trick is to check the thread depth- you may be able to go with a slightly longer bolt than what you had. More thread contact means a more solid connection. Also more surface for locktite to work on.

    Finally, be certain the mating surfaces are clean-crank and flywheel. Again with the acetone and lint-free rags.

    This sucks but you have to be meticulous with these details, even more so with a radical engine.

  6. #6
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    Just because it's new does not mean it's good, right f'ing hell, it's with everything.

    She's built like a steakhouse but handles like a bistro

  7. #7
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    I think it was most likely due to an improperly imbalanced clutch/flywheel combo inducing fairly heavy vibration into the bolt flange area. Bolt tensile failure is not really possible with the way this connection is loaded and much less likely. Bolts rely on friction to prevent backing out, and constant cyclical loading from imbalanced rotating mass is enough to back just about anything out.

    https://www.youtube.com/watch?v=IKwWu2w1gGk

    This shows just how quickly a bolt can come loose and back out.

  8. #8
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    Have you check the condition of your 20+ year old stock harmonic balancer? Is the woodruff key still in place? How is the rubber isolator? I ask because you got clutch failure, but it could be other failure that cause the clutch to fail also. It could be insufficient FW bolt torquing.

    Other have run this clutch with no issue.

  9. #9
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    Quote Originally Posted by M3poseur View Post
    Have you check the condition of your 20+ year old stock harmonic balancer? Is the woodruff key still in place? How is the rubber isolator? I ask because you got clutch failure, but it could be other failure that cause the clutch to fail also. It could be insufficient FW bolt torquing.

    Other have run this clutch with no issue.

    This is great advice and true on the general DKM clutch experiences. Engine was entirely rebuilt at time of clutch install and IIRC, a new balancer was used, but having the shop double check. This was a no expense spared build. Bolts were properly torqued, Loctite applied, and torqued checked a 2nd time.
    Last edited by wgknestrick; 01-08-2021 at 10:23 AM.

  10. #10
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    I don't have good information from my install.

    I think their kit came with bolts that I used and a tiny bottle of loctite. I replaced the rear crank seal at the same time so there's a good chance it got a healthy spray of brake parts cleaner in the threads there.

    Mine has not come lose as far as I've noticed in maybe 1000 miles, but I also haven't gone back in there to check.

  11. #11
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    Harmonic balancer was re-used from my original 70K mile engine and was inspected prior to install. I do share some concern on it though.

  12. #12
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    Quote Originally Posted by wgknestrick View Post
    This is great advice and true on the general DKM clutch experiences. Engine was entirely rebuilt at time of clutch install and IIRC, a new balancer was used, but having the shop double check. This was a no expense spared build. Bolts were properly torqued, Loctite applied, and torqued checked a 2nd time.

    have you taken a look at the new collab between brembo and TRD on their new racing axles? Maybe your CV wouldn’t blow out so fast next time just a thought

    i mean if you put pictures up maybe we could help

  13. #13
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    Quote Originally Posted by Brentinpdx View Post
    have you taken a look at the new collab between brembo and TRD on their new racing axles? Maybe your CV wouldn’t blow out so fast next time just a thought

    i mean if you put pictures up maybe we could help

    I have no idea what you are talking about or if this is even the correct thread you are posting in. Thank you.

  14. #14
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    After a month of back and forth, I finally got resolution on this clutch today. All 3 parties (Comp Clutch, BPC, and myself) are splitting the replacement cost of the clutch since no concrete failure mode could be determined. It could have been the clutch itself out of balance (Comp Clutch/DKM), installation oversight (BPC), or an issue with the damper used in the engine rebuild (myself/BPC at fault). I'm upgrading to a VAC/ATI super damper to ensure this issue can't happen again. While I can't say I'm happy that this all happened, it is about as fair of a resolution as I could've hoped for. It's a shame that I'll probably never know what caused this.

  15. #15
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    Really appreciate for the update. It’s nice to know the outcome even though it’s not the outcome you’ve expected. Enjoy the journey.

  16. #16
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    Quote Originally Posted by M3poseur View Post
    Really appreciate for the update. It’s nice to know the outcome even though it’s not the outcome you’ve expected. Enjoy the journey.
    I just wonder if it was the damper all along that caused all my woes with destroying my S52 (oil pump gear falling off), and then this.

  17. #17
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    Did you get the flywheel/pressure plate balanced before installed? This is probably the source of your issues. (Friend had similar problems with his S52 after installing aftermarket clutch that was not balanced before installation)

  18. #18
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    We did not, but the DKM comes as a complete clutch/flywheel combo that should be ready to install. It does not state that it requires balancing in the instructions, and you usually invalidate the warranty doing things like that. Comp claims all these are "factory balanced", but we both probably have our doubts.

    Again, we are all speculating and that is what caused this to be drawn out for a month. We are installing Nordlock washers on the new flywheel bolts as well. These really should be used way more than they are.

  19. #19
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    If it's balanced there'd be balancing marks on the flywheel at least.

  20. #20
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    Quote Originally Posted by 5mall5nail5 View Post
    If it's balanced there'd be balancing marks on the flywheel at least.
    Agreed, if there were no match marks on the flywheel and pressure plate, it was not balanced.

    Have fun pulling all this apart again if you don't get the assembly balanced before reinstallation.

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