Monday, 10 October 2011

Downpipe replacement: modifying the new pipe

While swapping out the old, rusty downpipe on the WRX STi I discovered that Subaru, in all their trickery, decided to make a small change to the exhaust oxygen sensor in the different years and models of their otherwise-ubiquitous turbo engine.

Note in this pic how there is an opening in the old pipe for an oxygen sensor, and none in the new pipe!



A bit o’ grinding and a spot o’ welding should cure this.


Another issue to be solved is the rather stubbornly unremoveable exhaust temperature sensor in the old pipe. Pictured here is the offending piece, as well as my righteous indignation:



No matter the method (PB Blaster, wrench, socket, vice grips, blow torch) it would not budge. Rust had sealed it in. No matter - the nice thing about parts you don’t intend to reuse is that you can cut the bejeezus out of them!

I really love my angle grinder :D

A few more cuts:


I really love my angle grinder :D

Some delicate cutting (so as not to damage the sensor):


And voila! Liberation!



Yes, it would have been much easier to just buy a new sensor. Didn’t you catch the part of this blog where I’m ridiculously cheap? Also, it’s another hard-to-find Japanese part.

In trying to get the sensor out of its old home I snipped the wires, thinking I could just solder them back together later. As it turns out, this isn’t copper wire and can’t be easily soldered. Twisting the wires together and thoroughly heat-shrinking them repaired my hasty cut.

Okay, so now the sensor is free - but since the hex drive got stripped to hell when I was trying to remove it, how on earth will I ever get it threaded into its new home? I’ll tell you how: Welding!

A giant nut from my collection of giant nuts is welded to the old, stripped sleeve on the sensor.

Now, on to that oxygen sensor.

The heat shield from the old pipe was drilled and ground until it was free:





…and the same was done to the new pipe:



Oddly, though the new pipe has no oxygen sensor hole (lovingly known as a “bung”), it does have a spot reserved in the white insulation for one.

Old bung gets cut out (I love my angle grinder):



A bung hole (tee hee) is drilled in the new pipe and we’re ready to weld the bung into the bung hole!





Done!

Heat shield from the old pipe gets reattached to the new one:



…and the new pipe is ready to funnel exhaust gases out to the back of the car as it was meant to.

Alright! The new pipe is ready. Time to reinstall. As Haynes is fond of saying, “reinstallation is reverse of disassembly” (or something to that effect).

No, Mr. No-Touchy was not any more fun being put back in than he was on the way out.

Done!

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