A 30 minute oxygen-sensor job on my 93 Civic has turned into a day long nightmare. Long story short I tried to take off my pre-cat oxygen sensor but didn't let the WD40 marinade long enough (or maybe it's completely seized), and I kept pushing until I twisted off the sensor, leaving the threaded piece stuck inside.

I've searched a bit, most people talked about using an extractor tool or welding a nut. I've tried the extractor tool (similar to EZ-out) but I didn't want to put too much torque; it just sortof stopped at a certain point and I suspect it won't go any more lest I crack the manifold or break my wrench; those threads you see on the inside of the sensor hole are from the tool. I don't have access to a welder or heat source. I've taken off the manifold already, thank god none of the studs broke.

At this point I'm considering taking it to a professional welder to weld a nut on, or else off to the junkyard to source a new manifold. But before I do that tomorrow, anyone have any other ideas on getting the stuck piece out?

Furthermore, does anyone have any experience with aftermarket exhaust manifolds? I'm not talking ebay headers. Local Autozone/Pepboys is selling OEM replacement part by Dorman and ATP, but reviews say that the port holes are too small, affecting performance. I'm running a D16z6, FWIW.

Pic of the disaster below. As you can see, not much to work with there.

 

could just drill it out.

 

Start looking for a new or used exhaust manifold or header (craigslist if you need it ASAP). Even if you remove the manifold and take it to a shop, they probably won't be able to get it out. Even with two adult males to provide torque with extended breaker bars, we could not get a frozen one out. We did shear it off at the manifold and ruin a socket in the process though. :\

Only option to save the part iself would be to have a machine shop bore & re-tap it.

 

Drill and re-tap.

 

Welp, an update:

So I had a brilliant idea to use a sledgehammer and hammer in a torx t55 socket into the hole. The socket was stronger than the o2 sensor metal, so the metal deformed and I had a beautiful star-shaped hole that my torx socket could bite on. Great success, right? Well, not really... After hammering in a T55 torx socket
Using a 1/2" breaker bar with the torx socket

I used a breaker bar to wrench on my newly formed hole and... no luck. That thing was seized in there real good. My torx socket itself started deforming and thats when I decided to give up. Maybe whacking in the torx socket just made it tighter, or maybe it weakened my torx socket, but whatever it was, it clearly wasn't going to come out.


So I ended up going to a junkyard. All the D16Z6s had cracked manifolds. Fortunately, I found a D16Y8 off a 97 Civic EX, and actually it turns out the manifolds are *exactly* the same. I had found conflicting info online that D16Z6 and D16Y* has different sized exhaust ports, but this seems to settle that debate. All the inlet ports were 35x45mm and the bottom holes also exactly the same, 25mm diameter.

Replacement manifold from junkyard. New one on top, old one on bottom
I bolted everything up and all now seems well, except that I now have a slight exhaust leak, probably because I didn't use new gaskets on the bottom two holes. I bought new gaskets to install, Fel-pro 60776, but does anyone known which side goes up?

Anyway thanks for the input everyone. I was hoping to get some miracle story about how the torx method worked (hence taking the pics) but ended up just replacing the whole thing. Hopefully this info might help someone else out there.