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    Thread: Crank Sprocket key sheared - salvageable? [pics]

    1. Member Legoguy's Avatar
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      05-09-2012 01:45 AM #1
      My crank pulley was wobbling and my timing kept drifting on me, and I finally figured out why -- the key in the crank sprocket sheared off, doing a little bit of damage to the crank nose. I actually figured this out when turning the crank by the sprocket bolt with a wrench -- it started to loosen just by rotating the engine by hand! It's my guess that the previous owner of this engine never torqued it right. I'm not 100% sure if my head/valves escaped this unscathed, but I do know that at some point the timing was at *least* 5 teeth (relative to the camshaft) off! I corrected the timing today before discovering this issue and the car ran fine until the timing drifted out of whack and the engine died again.





      Now, obviously I need a new crank bolt and sprocket, not too hard to get I don't think. The only thing I'm worried about now is if the wear on the crank keyway is going to cause failure again. As you can see in the pics, it definitely did chew up the lefthand side of the groove. I'm reluctant to use pins, since the other option at this point is to find a good shape 9A block and transfer my PL head onto it for (as I understand it) quite a nice performance boost - but quite a lot more time & effort.

      Opinions? Is my crank done? or should I just pin it?

    2. Member ps2375's Avatar
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      05-09-2012 02:13 AM #2
      For a repair in the car, pin it. I have in the past had to repair the same sort of damage, and I had someone add some metal with a welder and then I reshaped the key-way. But that was with the crank out of the motor, I suppose it could be done installed.

      And seeing the amount of rust colored powder in the pics, that could also be "normal" wear. The key gets hammered and rusts away.
      Last edited by ps2375; 05-09-2012 at 02:15 AM.
      Tradition is the art of making the same mistake repeatedly, on purpose.

      FS:MkI low back front seat upholstery(new)

    3. Member Legoguy's Avatar
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      05-09-2012 02:22 PM #3
      Yes, there was quite a lot of rust dust. Do you think I could get away without pinning it, just putting a new sprocket on and a new bolt and call it a day? Or do you think it might fail pretty quick with the nose of the crank like that?

    4. Member ps2375's Avatar
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      05-09-2012 03:54 PM #4
      The key is more for location than for drive. I would clean the snout of the crank, debur and put some red loctite (not a lot, but enough to cover the mating surface) and install a new sprocket and bolt and TQ to specs.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-10-2012 12:37 AM #5
      if you want this to never happen again, use the 1 way alternator pulley like the diesels use!

    6. Member Legoguy's Avatar
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      05-10-2012 04:49 PM #6
      I have the 6pt 10.9 steel bolt + 7mm washer versus the replacement which is a 12pt 8.8 stretch w/o washer - as I understand it, the 6pt/10.9 is *not* a stretch bolt. Can I reuse it? threads look healthy, just some residual rust from the disintegrated key notch. I'd honestly rather stick with the stronger steel bolt which is NLA from pretty much everywhere by now. I don't know why VW would have gone to 8.8 other than for cost savings - I hear a lot of horror stories of the 12pt bolts snapping.

    7. Member ps2375's Avatar
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      05-10-2012 05:21 PM #7
      I have never seen one break. My advice is go with the 12pt stretch bolt, I think it will hold better. I have no proof, just, that is what I think.
      Tradition is the art of making the same mistake repeatedly, on purpose.

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      05-10-2012 08:58 PM #8
      Quote Originally Posted by Legoguy View Post
      I have the 6pt 10.9 steel bolt + 7mm washer versus the replacement which is a 12pt 8.8 stretch w/o washer - as I understand it, the 6pt/10.9 is *not* a stretch bolt. Can I reuse it? threads look healthy, just some residual rust from the disintegrated key notch. I'd honestly rather stick with the stronger steel bolt which is NLA from pretty much everywhere by now. I don't know why VW would have gone to 8.8 other than for cost savings - I hear a lot of horror stories of the 12pt bolts snapping.
      bolts are not made specific as TTY bolts.. any bolt will stretch after you pass its yield point.

      its the torque spec that signifies a stretch bolt. because if you just torque a bolt to a regular torque setting, it wont hardly stretch.. (70 ft lbs)

      but, if you used a TTY torque spec for the bolt, then it will stretch once it gets past its yield point.

      44 ft lbs + 1/4 turn + 1/4 turn..

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