Here's what I've tried so far:
1) 22mm crows foot
2) penetrating oil
3) 7/8" O2 socket
4) Engine warm w/socket
5) Engine warm w/socket, w/1/2" drive
6) Engine warm w/socket, w/1/2" drive, breakover bar AND 2 foot pipe extension!

On the last attempt the socket just slipped and rounded off the damn O2 sensor.

Now that I've probably screwed it up any suggestions?

 

Well if it is a bad o2 (well its probably not worth using now its stripped), get the craftsman stripped bolt sockets. BUT not sure if they make one that big. My one set I don't think had one that big, but look around maybe another company makes them, or maybe a different kit from CM. They work wonders, and only about 15-20 bucks. They will bite into that rounded bolt and get it out. You will need the o2 warmer, then engine warm to get it off. I did. Torch it red. Mine wasn't rounded.
Mine was bad sensor so it didn't matter if I wrecked it.

 

you need a pipe wrench for plumbing work. remove the pipe with the sensor and put it in a vise. working on old cars is fun. :/

 

At this point the O2 isn't working so I don't care about it. I already tried slipping a regular deep socket over it but it wasn't deep enough and I can barely get to the thing while on the car.

That stupid O2 socket probably flared out under all that torque allowing it to slip and round the corners off the O2. I think it's time to pull the whole manifold off. I have a huge pipe wrench once I get the manifold off and on a bench (assuming I can get the manifold bolts off). Man this is a hassle.

 

use a torch to heat it up first

 

it would be kinda crappy, but you could always weld another o2 sensor bung in and leave the old one where it is.

 

I too tried everything to get it off, nothing worked. This is what I did; I used a hammer, broke the sensor off leaving just the nut on, and had my impact gun on it for like 1 min., then that bitch came off smoking. Good luck.

 

Try grinding the sides down on the nut part, then torch it, then get a big vice grips on it.

Or try welding something to the nut part.

 

remove header, then use pipe wrench and a BFH

 

yeah dude. remove the downpipe or header...

 

ding ding ding

 

Smoke a BIG joint and you will forget all about the Screwed up O2..(chuckle..where's the food?)
Sounds like you should use a O2 Socket??

 

1) Place pipe in vise attached to sturdy work bench
2) Torch til red hot (heat cycle it as many times as you like)
3) big honkin pipe wrench w/ 5ft pipe

Wear safety glasses during #3, because pipe wrenches are made of cast iron/aluminum. The wrench may break (read explode) from an idiot jumping on the end of an 8ft pipe...

 

If you can't/don't want to remove the manifold, I've got another idea

Spray it down with PB Blaster before going to bed
The next morning, spray it down with PB Blaster before going to work
When you get home from work, spray it down with PB Blaster a third time. Wait 30 minutes, then attempt to remove the O2 sensor.

The O2 sensor in the Cosmo downpipe was being very stubborn when I tried to remove it. After trying to muscle it out and finding the whole 20B engine moving on the mounts, I did the aforementioned trick using a 7/8" closed-end wrench and 13/16" wrench hooked onto the end, open end to closed end (for more leverage). The piece of pipe I used before had bent under the load, was too small to fit over the open end of the 7/8" wrench and too long to maneuver under the hood.

But since yours has rounded off, better break out the vise grips and clamp them on super-tight. Next time, remember the anti-seize