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strange flywheel wear pattern, '91 348

Discussion in '348/355' started by TomPDX, Apr 28, 2008.

  1. TomPDX

    TomPDX Formula Junior

    Mar 28, 2008
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    I searched for a thread on this, but perhaps my problem is unique. My '91 348 TS is in for a major. The bellhousing had oil contamination, due to a failed o-ring, so the clutch is being replaced. The problem is that the flywheel is worn and "heat checked" on only one half. It is like looking at two different flywheels photoshopped together. My mechanic, and his machine shop guy, have not seen this before, and that worries me. The other wierd thing is that the allen-head screw that locks the clutch assembly nut in place came unscrewed, causing damage to the small cover (with the cavallino). Any ideas on what could have caused the strange wear pattern? Any effect from the allen screw backing out? I'm sorry I don't have a photo of the wear, but trust me, it looks like two halves from different cars. Thanks brothers!
     
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  3. ernie

    ernie Two Time F1 World Champ
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    Any pics???
     
  4. TomPDX

    TomPDX Formula Junior

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    #3 TomPDX, Apr 29, 2008
    Last edited by a moderator: Sep 7, 2017
  5. Miltonian

    Miltonian F1 Veteran

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    Tom, I think the only way you could get damage like that would be if you installed the rear cover (with the Cavallino) while the central hex screw was backed out from the ring nut. There is supposed to be a fairly substantial air gap between the cover plate and the ring nut / hex screw. If the hex screw just worked loose, I can see it rubbing on the rear cover, but I don't think it would cause that big crack in the cover. Strange damage.

    I'd be most interested to see the unusual wear pattern on your flywheel.
     
  6. Miltonian

    Miltonian F1 Veteran

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    #5 Miltonian, Apr 29, 2008
    Last edited by a moderator: Sep 7, 2017
    This may be hard to understand, but I think this is what happened. Look at the color diagram. I think someone failed to screw the hex screw (yellow) into the ring nut (orange) before they installed the rear cover (brown). This has two effects. First, because the hex screw is actually hitting on the cover, it prevents the cover from seating all the way down against the bellhousing. That would be OK if the cover was JUST a cover. But the cover has a second function. It also seats the flywheel support bearing (blue) into the bellhousing (pink). Look at the joint between the bellhousing and the cover plate. If those two are not fully in contact with each other, then each time you push in on the clutch, that bearing moves backwards until it hits the cover plate. In other words, the entire rotating clutch assembly is moving back and forth. The bellhousing remains stationary, because it's bolted to the transmission case, but inside the bellhousing, the clutch itself is moving, which destroys the set-up height and sends everything out of whack (hence the abnormal wear pattern on the flywheel).

    Who did your last clutch job?
    Image Unavailable, Please Login
     
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  8. mseals

    mseals Global Moderator
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    Jeff,

    JEEPERS! Did you draw that up?

    Excellent post... and the mark of a real, true professional... care to make a trip to Kuwait for a week or so???

    :D

    Mike in Kuwait
     
  9. TomPDX

    TomPDX Formula Junior

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    Miltonian - I have seen your excellent diagram before in attempting to research threads related to my problem. I've also seen some of the back and forth regarding the function of hex screw. You are right, it is a little difficult for me to follow, but I think I understand. According to my mechanic, however, the cover was properly installed. He believes that the set screw was not properly tightened, and slowly backed out over who knows how many miles until it contacted the cover, then backed out the rest of the way causing the damage. But I think your theory still holds up, right? Because once the set screw had backed out, it would allow the clutch assembly to move back and forth even if the cover plate was properly secured. Is that right? (Although not as much as if the cover was not secured. I don't know who did the last clutch service. Most of the prior service was in the SF Bay Area, but I don't recall seeing a clutch service.
     
  10. Miltonian

    Miltonian F1 Veteran

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    If you look at the relationship between the flywheel, the bellhousing, the bearing, the ring nut, and the cover plate, there is no way that the clutch assembly can move back and forth unless that bearing isn't properly located. And if the cover plate was indeed installed correctly, then the only way the clutch can move back and forth is if the bearing is the wrong width. Otherwise the bearing is absolutely clamped into place. For now, I stand by my guess/hypothesis. The nuts securing the rear cover may have been tight, but was the rear cover actually tight up against the surface of the bellhousing??? Or was it jammed against the hex screw?

    No, I didn't make that drawing, I just colored it for clarity.
     
  11. TomPDX

    TomPDX Formula Junior

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    I see what you are saying. I didn't take the thing apart, so I can't say if the cover was properly secured or just up against the hex screw. But now I do see how that - and only that - would allow the bearing to move. Of course, I will have more info when the verdict comes in from the machine shop. If you are right, I may be less likely to be in the market for a flywheel. So I hope you're right! Thanks.
     
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  13. PAP 348

    PAP 348 Moderator
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    After seeing this pic, I reckon that the centre hex nut was left wound right out. They forget to screw it in, then put the cover on using the 4 nuts to pull the cover in, cracking it. :):)

    I could be wrong here, but I dont reckon that the hex bolt being left loose, would un-wind into that cover and cause it crack like that. Of course it would have the mark in there where it has been rubbing, as you can clearly see, but I dont think it would have cracked the cover. :):)

    If the hex bolt did come loose and wound out there being stuck and not able to fall out of the hole because there is not enough clearance, then I would think it would just sit there and eventually wear a hole in the cover. It is only cast that little cover. It would not have taken long. The same time, the hex bolt head would have been wearing down. But not by much, as its a steel bolt, not sure of the grade though? ;);)
     
  14. 2NA

    2NA F1 World Champ
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    PAP 348 and Miltonian are right. The screw might vibrate out until it contacts the cover (I really doubt it though) but there would be no way it could exert any real force against it. The last person in there did that.
     
  15. TomPDX

    TomPDX Formula Junior

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    Of course, if it did wind out, or alternatively, was barely in contact with the cover when the cover was tightened, it would unscrew itself completely once it came in contact with the cover (when the clutch was spinning in the "unscrew" direction). I think that the steel hex screw unwinding against the cover (it's just pot metal) would certainly be able to cause the cracks. And I may be giving the dolt too much credit, but you would think he would see the cover cracking as he tightened up the 4 securing bolts!
     
  16. PAP 348

    PAP 348 Moderator
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    Yes, you WOULD think that. :D:D

    Ive seen some rough sh*t in my time, so I wouldnt be suprised mate. :(:(
     
  17. ernie

    ernie Two Time F1 World Champ
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    Like a three legged coal mine donkey????????

    :p :D :D :D :D :D
     
  18. PAP 348

    PAP 348 Moderator
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    :p:p
     
  19. TomPDX

    TomPDX Formula Junior

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    Turned out the flywheel was improperly machined. Thankfully, it was serviceable. It has been machined back to Ferrari specs and is ready to install. I should get the car back early next week - just in time for some great Northwest weather!
     
  20. No Doubt

    No Doubt Six Time F1 World Champ
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    Cool! Plus the bonus is that machining the flywheel took a little bit of weight off of it. You should love the way she runs now!
     
  21. PAP 348

    PAP 348 Moderator
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    Good to hear you will have it back on the road soon Tom. :):)
     

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