yeah some of these just don't play ball . seized bolts and nuts and the space is tight compared to alot of cars you'll work on.
i left my manifold on so had to take out the radiator for room to get the housing out.

 

To the OP- do you definitely have to take off the undertray to do this or can you get to the stock O2 housing bracket with it still on? I know I can unbolt the downpipe with the undertray still on.

Thanks!

 

Is it possible to use bolts (instead of studs) on all 5 of the 10.5 hotside's connections to the o2 housing?

 

So the answer is that you can only replace one of the studs with a bolt (the bolt showing in the pic below). Due to the shape of the o2 housing, it's not possible to replace the other one with a bolt. There's not enough space to thread a bolt through this hole.

 

I have my O2 fastened with 5 bolts and no studs. So, it can be done.

 

Is your o2 a dump? Maybe it's shaped differently, but on a Megan o2, it won't happen.

 

The trick is that 4 of the bolts can have the 17mm bolthead size whereas the 5th bolt(the lowest down) has the same bolt shaft diameter and thread but a smaller head size(14mm I think). Do you comprendo?

 

No mine is not a dumpster. It is an EBay O2 housing.

 

Do you have a part number for that particular bolt?

 

I pretty much explained it in my post #352. I used a non-Mitsu bolt that had a smaller head size. I fished it out of the Planter's Peanut tin can. It is the same shaft diameter and length but has a smaller head.