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Stripped threads

Discussion in '348/355' started by Saint Bastage, Jan 29, 2008.

  1. Saint Bastage

    Saint Bastage F1 Rookie

    Jun 1, 2007
    2,548
    Connecticut
    Full Name:
    Lane
    My Major is nearly complete and I was just made aware of a problem that scares the crap out of me. I'd like your opinions please.

    It seems that some previous owner or mechanic crossthreaded or otherwise screwed up the threads for the transmission dip stick. They repaired that problem by installing a Helicoil. My mechanic had some difficulty removing the dip stick because the helicoil had broken and was spinning in the hole. As I understand the story now, the helicoil apparently cracked a thread at approximately the same depth as the dip stick plug "max reach" meaning that some portion of the coil remains in the hole and (hopefully) the remaining piece was removed, intact. The dip stick plug cannot reach those threads and was therefore replaced with a longer bolt to seal the box.

    Here's the fear...how can I verify that no smaller portion of the threaded helicoil has fallen in to the gearbox. I know I have to replace the 3rd gear synchro soon, but if there is a chance that a piece of coil is in that box, the car should not move, period. Just that little piece can change the job from a $5000 gearbox rebuild to a $25,000 gearbox replacement.

    Are helicoils made of ferrous materials? Will the magnetic drain plug hold any possible piece away from the gears (assuming if gets captured)? Is oil flow dramatic in those boxes?

    Next question...once the gearbox is disassembled (for the synchro job), what is the "proper" way to fix these threads? It seems to me that installing a small metallic insert is just stupid.
     
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  3. plugzit

    plugzit F1 Veteran
    Rossa Subscribed

    Dec 1, 2004
    7,348
    Redondo Beach, CA
    Full Name:
    Bruce Bogart
    If you pull the inspection plate off the bottom of the tranny, you should be able to see if there's any part of the helicoil in there.
    How to fix it? Kinda hard with the tranny in the car. If pulling the inspection plate gives access to the bottom of the hole, you could drill it out and rethread it a size larger, then clean out the aluminum shavings. Maybe risky, but an aluminum shaving or two left in is unlikely to do any damage. Okay, I didn't say that. Instead, pull the entire tranny, disassemble it, repair the hole by welding, redrill, rethread, clean it, reassemble it, etc. Things in the bottom of the pan tend to stay in the bottom of the pan unless you turn the car over.
     
  4. vvassallo

    vvassallo F1 Veteran

    Aug 4, 2006
    8,213
    Palos Verdes
    Full Name:
    Vince V
    Agreed. I wouldn't panic. Apparently, no one told that mechanic about helicoil usage - there should be for external use only, not engine internals for this reason. Drill and tap to next higher size, or larger and use a bushing. The odds of trans damage resulting from a miscellaneous HC part in there are pretty slim assuming it's not a sizeable piece. I assume that the dipstick still screws in meaning the errant HC piece is not that large.
     
  5. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    In my very non-professional opinion, flush the gearbox, install a time-sert, and fuggadabout it.
     
  6. Saint Bastage

    Saint Bastage F1 Rookie

    Jun 1, 2007
    2,548
    Connecticut
    Full Name:
    Lane

    What be that?
     
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  8. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    It's like a Heli-Coil, but stronger/better.

    http://www.timesert.com/

    I had never used one before --- until I stripped the threads on my oil tank. Tom Jones @ Sport Auto (Summerfield, NC) was incredibly generous and loaned me his kit on a 25-minute advance cry-for-help one Saturday. It was brainlessly simple to use, and extremely strong. Check out the page linked above to see how they work.
     
  9. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
    5,964
    Milton, Wash.
    Full Name:
    Jeff B.
    Might be a good idea at this point to remind the brothers to put a dab of anti-sieze compound onto the threads of the transmission dipstick while it is out. Those things have a reputation of being really hard to break loose sometimes.
     

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