Rookie Mistake! What are my options?

Craig Roche · 04-21-2004, 07:51 PM

I needed to replace (or thought I did) the oxygen sensor on the catalytic converter and totally destroyed the threads. Is there anyway to fix this blunder or will I have to replace the cat? Please advise. I really screwed myself here!!

Jim Sims · 04-21-2004, 07:57 PM

Exactly what did you do? The bung is tapped with a spark plug thread; there are thread restoring taps for this thread type available. Is there a remanent of the O2 sensor in the bung?

klaucke · 04-21-2004, 08:02 PM

Depending on your situation...
tack weld a nut on above it or next to it to thread the sensor into,
heli-coil it,
retap the hole larger, get a bolt that size, drill through it and tap it for your O2 sensor,
remove your cat = gain hp (sorry to the greenies)

Eric Coffey · 04-21-2004, 08:02 PM

Sounds like a good excuse to buy a Euro pre-muffler!

Jim Sims · 04-21-2004, 08:05 PM

http://www.ctatools.com/catalogs/threadre.pdf

Craig Roche · 04-21-2004, 08:08 PM

Here's some photos. The threads on the cat look much better than the O2 sensor but I was thinking, how could the cat be ok with the threads so bad on the sensor??

Craig Roche · 04-21-2004, 08:09 PM

Jim Sims · 08:32 PM

I have been through this very experience; I suspect you have left the O2 sensor threads in the bung (inside the bung threads) in the CAT. Get something fine, sharp and strong and pick them out. You may need to use a thread restoring tap to assist the process. That's what I did and the bung threads were fine. Jim

VincentVega · 04-21-2004, 08:18 PM

You're fine man, relax. From the photo it looks like the O2 sensor is toast but the cat is fine. Jim's dead on with a pic or better yet chase the threads. No big deal.

Craig Roche · 04-21-2004, 08:22 PM

Hey Jim - Thanks for the link and also the encouraging words! How do I determine the size tap to get? Is it 14mm? ???

Klaucke - Thanks for the input, I hope I don't need to do that much! I would loose the cat!!

Jim Sims · 04-21-2004, 08:28 PM

I frankly can't remember; I used a two sided tool (14 mm and 18 mm) and used the side that fit. Measure the bung. You may be able to find the tool locally as they're rather common. Jim

brcorp · brcorp's Garage

Craig,

I may have the correct tap, if not Harbor Freight has them. Good for a couple of uses then the trash. I doubt you've done any damage to the bung threads. Do you have an O2 sensor to replace the old one? Let me know if you need some help.

Matt77Euro27 · 04-22-2004, 06:27 AM

If the threads in the bung are toast, go to a muffler shop have the old one cut off and a new one welded on. Should be cheap. It might even be cheaper than the tap.

18mm x 1.5 off the top of my head.

Matt

chrisp · 04-22-2004, 07:17 AM

You may want to start by getting a new O2 sensor and trying to screw it in by hand. I just put my back in last night and it screws in freely and only about 2-3 turns till it stops. Try this before you go through effort and expense to chase (clean) the threads.

Actually the way I would personally go about this is since this is not a strutural bolt and it doesn't hold anything together I would just screw it back in and leave it. Even if it's crossed threaded. You can always chase the threads later if you want to put a new O2 sensor in. I bet within time you will decide to disconnect you O2 sensor like so many others have.

Craig Roche · 04-22-2004, 08:45 AM

brcorp Bill, I sent you a PM

Thanks all for the input! Doesn't seem so bad now.

I'll do the "chase the threads" thing and I'll post the size.

Thanks again to all!!

klaucke · 04-22-2004, 04:54 PM

If you end up buying a tap, I recommend you spend a few extra dollars and get a good one, i.e. a Craftsman or Vermont American. I fine the 'made in china' type to destroy threads [as in open them up too big] because they are so cheaply made. Everytime I need a metric tap, I go out and buy a good one and add it to my set. Actually, I recently just splurged to get a whole set of good ones. This is one of the few areas where I actually spend the couple of extra dollars.

Also, if you get most of the O2 threads out of the bung threads with a pic, you can take a bolt of the correct size, cut about 1/4 of a pie out of the end, and use that as a "Polish tap"

Jim Sims · 04-22-2004, 06:34 PM

You don't want a thread cutting tap but a thread "restoring tap"; this is what the "two-ended" unit sold in the above listed link is. Jim

fred cook · fred cook's Garage

Go to your local NAPA or equivalent auto parts and ask for a double ended spark plug tap. It will have both 14 mm and 18mm taps so you can pick the size you need.

Good Luck!

Fred Cook
'80 911SC coupe