How To: Replace an Exhaust Flange

[ElderGeek]

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. Depending on how good you are will determine if you need to dress things up after the plasma cut.
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.......

[ElderGeek]

I picked up a piece of 5/16” steel at Industrial Metal Supply, cost two bucks for enough to make four flanges if I needed to. (My wife could not believe I did not have a piece of steel that would work. I was too.) I did notice the stock YFZ flange is steel and ¼” thick. It does show a slight bend so I went with 5/16”. It might be over kill so you could try ¼” if a quarter pound of weight is an issue for ya!

I covered the steel with painters tape so it’s easier to write on and used the old flange as the template and traced it out. For some reason I didn’t take pics before drilling but you can see below how I did it. This first tracing is a rough layout. The reason is when drilling with hole-saws, they tend to float around. This is due to the amount of wobble your drill press has and how well you can clamp the piece down while drilling. A hole cut with a hole-saw will always be bigger than the size stated on the hole-saw! Which is why hole-saws are not tight tolerance hole cutters.



As it turned out a 1-5/8” hole-saw is just a tad under the diameter of the header pipe. So a little float/wobble was acceptable. I clamped everything as tight as I could and used a lot of oil while cutting to help keep the cut smooth.



These were taken after cleaning up, there was a pile of shavings and oil when I was done.



How’s that for a smooth cut?



If you use too big of hole-saw or things float too much during the cut then you will not have enough ‘shoulder’ for the flange to catch the ring and hold it tight. The ring will try to squeeze through the flange hole. Double check this before you finish the first hole cut. Once the hole-saw has made a cut into the steel down past the saw teeth, stop and lay the ring on it to see if the size is going to work. The worst case is its too big and the ring can be pushed through the hole, time to find a smaller hole-saw or better drill press or vise, the better case is it’s a touch small but not more than a die grinder and your patience can handle. The best is its just right with enough shoulder.



Now we tape up the steel again and do a final layout. Cut the tape from the hole and lay the old flange on there. Align the hole to the flange keeping both holes centered. Then trace the outline and the two other holes, the sharper your pencil the better.

After tracing take a straight edge and mark a center line intersecting the center of all three holes. This gives you a visual to confirm things are straight and lined up. If you don’t like what you see, peel the tape and start over. You may ask; “Why didn’t we do this before we cut the big hole?” The center line will float due to the nature of the hole-saw cut. The center hole determines the location of the bolts holes. If we were doing this on a mill you could lay it out all at once.

I drilled the bolt holes then did another final ‘edge’ layout.
Here you can see I also scribed straight lines to make my rough cuts.



Rough cuts are done and ready to hit the grinder.



Now would be the time to ‘test fit’ the flange on the head to be sure the bolts holes are correct and it slides on the studs without a hammer. Any drilling or grinding will be a real pain after the ring is welded back on. To make things easier I didn’t grind away as much and made straight edges.



All dressed out after the belt sander. Ready for paint.



You could powder coat it. I went with high temp flat black.



Why did I make two? I always make two of these kind of things. The second one always turns out better. And I have a spare.



Now it’s ready for the welder. Don’t forget to slide the new flange on before your weld the ring back on. That would cause the header to turn into a very fast projectile or have a unique ‘race bend’ added to it!! Note in the pic below that my marks are not exactly true. It will be at weld time, you can bet on that!




On to Part 3......

[ElderGeek]

Welding is complete. I used Arizona Custom Machining to do the stainless welding. He was close by and only charged me $20.


The weld bead all ground down a smoothed as before. I didn’t go to the “Port & Polish” level of finishing, but it’s pretty damn smooth. When grinding and sanding down the weld bead be sure not to cut into the pipe. It’s very thin and any removal of material will weaken it. Just go slow and check it a lot.


Installed ready to run!!


So


So there it is. Shouldn’t have to worry about it ever again. Be sure to check the bolt torq after running a short while and ever so often after that. A loose or leaking header can cause valve warping. After a couple of good rides it should be good to go.

If you ever wanted to change out that bent up exhaust flange, now you know how.

[Jeremy]

Thanks Mike - posted to the home page - http://www.arizonaquads.com

[azkfx450rider]

good write up, although i dont have 1/4 of those tools haha! but hey a lot of people do, thats why its always good be good friends with a few shops

[Quadracer269]

Fantastic write up.... Good skills you have there also....

[ElderGeek]

Muchas Gracias!!

I have two others on how to lower you stock YFZ for TT racing the knobbie class. But it's kind of a mute point right now.

[EJS0806@aol.com]

Nice work just wondering though i have the full yoshi on my LTR and there are the welds for the heat shield. Should i cut them off to remove the flange? I cant get them past it and mine is bent like a U? any help would be greatly appreciated.

[ElderGeek]

Is this what it looks like?



If it is, you would still need to cut the pipe at the 'Step Up' section. So if that is the direction you want to go then yes, you would need to cut the heat shield mounts and the step up joint. I would bet the first section slides into the step up section. This keeps the inside of the pipe smooth with no restrictions. If you cut it and try to match how it was assembled at the factory, you will shorten the length of the pipe changing the 'Tune' of the pipe. If you butt weld it instead you will have a weld ridge, (if the weld is done correctly) that you cannot clean up.

Another reason I wouldn't go that way is you now have to weld the mounts back on. A good Tig welder should have no problem but the material is alot thinner. If a hole is blown through, you would again have no way to clean up the weld on the inside of the pipe. The other issue is you need to be very sure you weld the step up section back in the exact same position, (rotation, linear axis, and length) or it and more inporatantly the can, might not bolt back on the bike.

While doing it the way I did requires a dremmel tool of some kind to cut the the inside weld and then dress it out after rewelding, you have more material to work with as the collar will absorb a lot of the heat and you have less of a chance of messing up the angles of the system as a whole.

The other way is to take it to Terry Design Concepts, a Site Sponsor and I am sure he can take care of it for you.

[EJS0806@aol.com]

Thanks for the great help