BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > DIY Guides > DIY -- Repair damaged thread with a HELICOIL

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      05-13-2012, 02:49 AM   #1

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Exclamation DIY -- Repair damaged thread with a HELICOIL

Vehicle: '09 E93 335i

Disaster! I cross threaded the mounting bolt for a M3 Guide Rod at my 3's Bearing Carrier!

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After a lengthly bout of execration, steely calm engulfed my wah.

I knew what must be done: Travel, to Napa Auto Parts, there to select a M12 x 1.5 [12 mm fine thread, blue pkg] Helicoil installation set.

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Returning to my ride $80 lighter - Amazon much less but preferred not to wait - angst caused beads of sweat to form.....it was a warm day.....and I had never done this before....

First things first. Verifying that my mount bolt was spinning freely, this job did not require drilling out the threads. Some jobs do -- but my bearing carrier threads were completely stripped out.

I removed the bolt - had damaged threads near the tip which crunched & munched all bearing carrier threads going through. Only when the bolt was fully 'threaded' in did I find it could not be torqued! Nothing left to torque against.

Ran a cylindrical magnet through the hole - came out with a large ammt of shredded thread, leaving the hole more or less clean.

I inserted my tap into an Irwin adjustable tap socket, Home Depot, to cut threads into which the Helicoil will thread:
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Name:  [01] 12 mm Tap with Irwin Holder.jpg
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The tap supplied is of the self-guiding type. Just start it in the hole....

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....and ratchet until the tap has cut all the way through:

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Then, the Helicoil, shown here with plastic install tool and threaded metal shank to thread the Helicoil into the hole:

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Drop a Helicoil tab first into the plastic installer....

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Insert the threaded shank....

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Turn shank until a thread or two is exposed. Tab should be at the tip:

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Blow compressed air through the hole w/newly cut threads to remove debris.

Insert Helicoil tip into hole to be repaired and, holding the plastic installer with a wrench, turn the shank, thus threading the Helicoil into the threads you've cut for the purpose:

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When the Helicoil's fully installed, thread the shank out, leaving the coil in:

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The tab can be punched off, or left in for the bolt to snap it off as I did:

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When the mounting bolt's ratcheted in, it threads into the Helicoil which is designed to press against the threads cut with the tap. Result: Successful repair - a new bolt torqued normally to 100 N/M +90

I used Permatex 81343, Ace Hardware, on the threads.

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Job done!

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TIP: Love my GearWrench electronic torque wrench plus angle....

Last edited by CALWATERBOY; 03-22-2014 at 07:05 AM.
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      05-15-2012, 02:46 PM   #2
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Solid write-up! I stripped a water pump bolt on my old SR20 build. After I changed my underwear I used one of these kits, problem solved.
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      05-15-2012, 02:49 PM   #3
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Drives: 2010 335i Xdrive
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Garage List
Great write up!
2010 E90 335i Xdrive| Titanium Silver Metallic | Black Leather | Premium, Sport, Nav, Cold | Steptronic | matte black grilles | Cyba scoops | pinstripes | Rear Fog Mod | Clear Reflectors | WeissLicht AE |More to come...|
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      05-17-2012, 05:27 PM   #4
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Drives: E90 335i LCI
Join Date: Mar 2012
Location: Irvine, CA

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Great write up. Hopefully I will never have to use it. I think having to re-tap/thread a bolt hole (especially a hard to reach one) has to be one of the most disappointing, aggravating and frustrating things ever!
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      04-17-2013, 07:56 AM   #5
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Thanks for this! I did the same stupid thing this weekend. I had to drill out my hole though. The hardest part was sourcing a drill that would fit in there! I did the other guide rod which is harder to access. Luckily 5 trip to home Depot later, I found the perfect drill. Also, 31/64" is the correct drill bit to use. Don't expect to find that at Home Depot or Lowe's either.
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