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How To: Replace an Exhaust Flange
I recently picked up used Dasa pipe for my YFZ. Everything is great except the flange that bolts the header pipe to the head. It is bent like a 'smiley face' and all chewed up from the nuts. It looks like the previous owner, (who will remain nameless....) had a problem getting this thing to seal at the head, and maybe applied a bit too much 'Umph' when tightening things down. Or things worked loose, who knows.
This is what I have. I'm sure many off you have seen this before. Other than a bling factor and/or weight, I don't know why Dasa, (and others), made this out of aluminum. This is a 'clamp' basically, and is under a good amount of stress, along with extreme heating and cooling. Aluminum does not have the "memory' steel does so it takes the 'smiley' shape over time. This pic doesn’t do it justice, this thing was really warped.
Time to replace that flange. Now before you jump into this, one needs to have the following tools. You don't need to own them, just have access to use them. It can be done without some of them but then it makes the job really 'manual' and not worth the time. You would be better off sending it in the Mfg and have them replace it, or buy a new header pipe. But I am a tight ass and will usually try to fix things at least once before replacing.
A quick side note: I did not call Dasa to see if they would sell me just the aluminum flange. This would be easier if you do not have access to the tools or the skills required to make the flange. I also did not go to a muffler shop or even a racing shop to see if they had a flange of the correct dimensions. So you could try these routes first.
Must have tools:
A: 1-5/8 Hole-Saw a good one that doesn't wobble. Size is determined by your header pipe.
B: Drill bit for drilling the header bolt holes. I used 3/8" to match the original.
C: Bench or floor drill press, (check for chuck wobble!!) A hand drill cannot be held steady enough for this cut.
D: Dremel or other cut off tool with a handfull of cut off blades. (I used my air tool with Dremel blades as they are very thin & I managed to get it done with only one due to my steady hand and perfect control.
Makes life easer tools:
A: A bench vise
B: Hand held, floor or bench mount Band Saw,or Saws-All, (something to cut 1/4" or thicker steel)
C: A plasma cutter would work well too.
D: Bench grinder for shaping, can be done by hand but will look like it.
E: Bench sander for final dressing, same as above.
The Dasa Pipe is all stainless. The weld for the 'ring' is on the inside of the header, right at the outside edge. I decided to cut it with my air tool, right at the inside edge of the weld to remove the ring. (blue line) The idea is to cut just at the inside edge of the weld to free the pipe from the ring.
Note: I do not know if this is standard on all exhaust headers so yours may be welded differently, which would change the way you would cut it out. Or if you can cut it out. The face we are looking at on the ring must remain undamaged as this is what seals via gasket to the head. Any cuts, dings, scratches, etc. will allow exhaust gasses to leak. Not good.
The wall thickness is very thin, so be careful not to cut too deep. You want to cut just the pipe and not into the ring if you can help it.
I backed up both sides of the Dremel cutoff blade with thicker blades to keep it from flexing.
Before you start cutting you want to mark the original location of the ring. The ring needs to be welded back in the exact same position. If it is not then the header and slip-on may not bolt back up correctly, if at all. It doesn’t take much ‘shift’ here to really funk things up so mark it well. I traced a line on the back edge if the ring all the way around the pipe. I also marked three other perpendicular lines about 33 degrees apart, marking one of those with a letter to know I have it in the same orientation as before the cut. You can’t see the other two lines in this pic.
Once you made your cut all the way around, you can test to see if you are deep enough by trying to tap the ring off, all the way around. I did this a few times until I reached the proper depth, the first time it did not move at all, then one side just started to move, I continued cutting, then tapping slowly and it finally slide right off. If one side moves and the other does not, just cut a bit more where it’s needed. Don’t get all excited and start slamming away in the ring and tear the header pipe. Cut a little, tap a little, cut some more, tap some more, until it slides off.
If you do it right the end of the header pipe will look smooth and clean, like this.
Now slide off the old flange, gently hammer it out flat and you have you template for the new one. Some may ask, “ Why don’t I just put the old one back on after I hammer it out flat?” You could in a pinch, you could even flip it over too, but it will bend back into a smiley before too long, so just fix it right while you have it apart. Besides I don’t think you would get to do this more than once as we only have so much space to weld with, basically the thickness/depth of the ring. The new weld will be on the ‘fat side’ of ‘in the middle”. Any ‘deeper’, like a second or third cut would push things too far into the ring making it more difficult to weld back up. And it could possibly cause a fatigue failure down the road due to not having enough of the header pipe supported by the ring. In other words not enough of the header pipe is slid into the ring at the weld point.
Now on to Part two.......
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