I really don't like it when I have to spend a bunch of time fixing something on the car that was recently working just fine. That very thing happened to me recently. One day, the car developed additional noise under the hood. I noticed it immediately after starting it up. I could tell it was an exhaust leak. After feeling around for a little bit, and only slightly burning my fingers, I felt an exhaust leak where the individual tubes come into the collector. Unfortunately for me, it was on the engine side, where I cannot get in with a welder.
Since I cannot stand the sound of an exhaust leak, I ended up spending quite a bit of time to fix it.
The pictures on the right were taken in reverse order (during assembly), but for clarity I'm going to present them as if they were for disassembly.
First, let me explain why I chose to keep the stock header rather than upgrade. Since I had to have everything apart anyway, it might have been logical to replace the stock style header with a better performing alternative. Well, given that most people report only modest gains at the top end, and that headers can be expensive, I felt it wasn't worth it. Also, the stock unit seems well built and designed, so fixing and replacing it seems to be a good alternative. Besides, I might have the opportunity to make it perform just a bit better…
To get at the header and heat shield efficiently, I first removed the air box, pulling it out of the way. I disconnected the air hoses from either end, took out the 3 bolts holding it in, and then slipped a flathead screwdriver into the loom retainer to open it and slip out the wiring. With that, I could move the box out of the way.
Then, I removed the 10mm bolts from the heat shield. Unfortunately, one of them snapped off. Upon later inspection, I found that this was a combination of being the wrong bolt (crossthreaded) and the heat-induced rusting. I had to tackle that later.
With the heat shield off, I could get at the header bolts. It's pretty easy to remove all of these with a standard socket wrench and a short extension. I also removed the three bolts holding the header flange to the exhaust pipe. Unfortunately, I found out that I could not remove the header from the studs without allowing the exhaust pipe to move side to side. This was restricted by a clamp that held the exhaust pipe to the bellhousing bolts. Upon removing the two bellhousing bolts, the pipe moved, and I was able to remove the header. Oh yeah… I pulled the oxygen sensor before all this too.
With the header out, I found the crack between two of the exhaust tubes. I cleaned & welded it. I also cleaned and welded for potential cracks at each joint. Given that the whole reason for this job was to silence a noisy exhaust, I couldn't put it back together without repairing the heat shield bolt. If I didn't fix it, the shield would likely vibrate against the headers, creating quite a racket. I first tried an ez out, but ended up snapping the tool. So I cut out the nut instead, leaving a gap. I then welded in a new nut of suitable size -- something for which I had a short enough bolt to thread in without hitting the header.
With the header out, I inspected the ports. The quality of the welds was good, but the bead extended into the port area, potentially blocking some of the exhaust flow. I doubt the obstruction has a significant effect on power. However, I did clean up the ports up a bit using an air die grinder and grinding bits, with the results shown in the pictures. I was fairly conservative, as I didn't want to reduce the strength. Anything I can do to clean up and make subtle changes to improve flow in and out of the engine is worth it, especially if it can be done with just a bit of time.
After that, I sandblasted the header & heat shield, blew off the excess sand, and put on a coat of silver high temp paint. It just makes sense to clean it up before putting it back together.
As a final touch, I replaced the oxygen sensor with a new one. At about $25 for the stock-style 1-wire sensor, it makes sense to just replace it. When reassmebling the header, I reused the copper gaskets that were on the car, putting a fine layer of high-temp silicon gasket sealer on them. However, I'm not sure if copper gaskets even require that to be reused. One trick when putting something like a header back together is to start all the bolts before tightening anything. This gives you some ability to move the system and line some of the harder items back up.
With that, I had everything back together. The leak is gone, everything is clean & painted again, the ports have less restriction (no, I did not notice any performance gain), and the oxygen sensor is new, which may increase my mileage. While it's a shame to have spent the mornings one weekend to fix something without adding performance, I did make up for it by improving subtly in a couple of areas.
