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Muffler Reconstruction – Part II

February 20, 2009

In the last post, I had just bought the stock 1098s mufflers.  Now for the deconstruction / reconstruction.

Stock 1098s Pipe (1 of 2, of course!)

Stock 1098s Pipe (1 of 2, of course!)

The first thing you notice with these mufflers is that they have a series of rivets around the front (engine) end, and the rear end (the exhaust cap).  I decided to attack the front end first.  The rivets drill out quite easily – the only thing to worry about really is that you don’t use too big a bit, and enlarge the holes.

Drilling out the rivets

Drilling out the rivets

Once all the rivets are drilled, they need to be punched out of the hole.  I used a small nail punch and a hammer – they really only need a slight tap.

Punching the rivets

Punching the rivets

The next step is to use a wide-bladed screwdriver placed up against the lip of the cap that you want to slide off.  Then, carefully, a few taps at a time on each side, hammer the cap off.  Again, if you’re careful and patient, it won’t mark the cap, and in no time, it’s off.

Killing the Cat

Inside this cap is a steel cylinder, and inside that, the catalytic converter.  Now these things are essential for the road, ripping all sorts of nasties out of the exhaust.  As you can see in this photo, they’re essentially a whole lot of very fine metal, honeycombed into the cylinder.  Sort of like a heavy duty foil of some sort.  If you hold them up to the light, you can see through them.  When the exhaust runs through them, the thin metal foil heats up to red-hot, and burns the bad stuff to a powder.  All good stuff, but just a little too restrictive for race mufflers, so they have to go.

The Catalytic Converter

The Catalytic Converter

The problem with this is – they’re an absolute bitch to get rid of!  The foil is welded or glued to the sides of the steel cylinder, so they don’t tap out easily.  After experimenting with the first muffler, I decided that the best way to get rid of them was to cut the cylinder in half, shortening it.  Then, the theory went, it should be easier to prise / tap this thing out.

Use an angle grinder with a cut-off wheel to cut the cylinder in half

Use an angle grinder with a cut-off wheel to cut the cylinder in half

Once the cylinder was cut, I decided to tap out the cat, using my old wide-bladed flat screwdriver, and a mallet.


I started bashing away at the cat, screwdriver pushed through the exhaust pipe end, and mallet swinging madly.  Nothing!  It wouldn’t budge at all.  More bashing.  Still no movement.  It was then that I noticed – I’d punched the screwdriver right through the steel cylinder wall!

See the nice hole? D'oh!

See the nice hole? D'oh!


A change in tactics had me using a fine flat-bladed screwdriver, prising the glued cat material off the walls.  I worked my way around the cylinder as best as I could, then used a large socket on the end of a socket extension rod, pushed through the exhaust pipe, and whaled on that mallet again!

Dead Cat!

Dead Cat!

T’Other End

Using the same technique as above, I then drilled and punched out the rivest from the cap end, and tapped the cap off the outer cover.  Once it was out a little way, I then tapped from the engine end, and the whole tube slid out.  You can see that sandwiched between the inner muffler tube and the outer skin is some muffler packing material.  It was intact, and in good order, and I decided that I would try and save this – for both insulation and sound quality reasons (didn’t want a tinny, harsh sound).

The deconstructed muffler

The deconstructed muffler

Once apart, the end cap had to be removed from the muffler.  The best way to do this is with an angle grinder and a metal cut-off wheel, although you could also use a Dremel if you were patient.

After cutting the cap off, you can see that the cap has a skinny tube that fit inside a hole in the rear baffle.  What this means is that the exhaust gasses have to flow from the engine end, through the catalytic converter, to the rear of the muffler, then back through a hole to the middle section between the two baffle plates, and then back through this skinny tube to the exit.  Too restrictive!

The baffles.  The tube goes up that centre hole.

The baffles. The tube goes up that centre hole.

The easiest way to fix this problem was to cut off the tube.  I’d seen some people who attacked this by completely removing the tube from the cap, and enlarging the exit hole.  However, I decided to keep a small section of the tube in place for the moment.

The end cap, with the tube cut off

The end cap, with the tube cut off

One final thing I needed to do was to remove the bits of the rivets from the end cap.  Once you punch them through, they are stuck inside the end cap, and there’s seemingly no way to get them out.  However, if you look closely at the design, you’ll see that one of the holes is not used by a rivet – the one where the stainless steel bands on the two mufflers join together.  So, using a larger drill bit, I drilled this hole out, and shook the rivets out.


The next step was to weld the cap back on to the muffler tube.  This should be easy!  I actually went down to the hardware, and bought a cheap arc welder.  Now the last time I welded at all was in technical studies classes at high school!  Woah!  It’s not that easy, as it turns out.  The muffler material is really quite thin, and the arc welder was blowing holes into it with great abandon.

I turned the amps way down, and decided to just tack the cap into place.  This was a lot more successful!

Chris's Crappy Welding

Chris's Crappy Welding

The final step was to get some muffler putty, and work that in to the gaps left by the welder.  This stuff is amazing – but you do need to make sure you wire-brush the area well before you use it.  It also helps to wet the area, which helps the putty work into the gaps, and helps it stick to the metal.

I left that to dry overnight, and came back the next day for the finale!


The final step was to slide the muffler back through the fibreglass, and rivet the caps on. That wasn’t quite as easy as it sounded – the first few attempts had me ripping the fibreglass matting.  I then decided to get an old plastic shopping bag, cut the bottom out of it, put that inside the outer case, then slide the inner case through the bag.  That worked well, and the bag was easy to remove once the muffler was halfway in place.

Then, a little muffler putty around the cap end (overkill), and it was tapped into place until the rivet holes lined up perfectly.  The final step was to put the exhaust end on, and again, a little muffler putty, and a few taps, and it was all good.

The very final stage was to rivet the caps back on.  This was easy – the only thing to watch out for is that the exhaust cap end can only take very short rivets – so make sure that you have the right ones.

Modified mufflers on - and originals on the floor

Modified mufflers on - and originals on the floor


There were a few little hiccups along the way, but all in all, I had a good time out in the garage with the tools, and was very pleased with the result.  The sound is superb!  I have taken a few short videos of before and after, and in the next post, will link to these.

I’ll also put them to good use very shortly – trackday coming up!!!

3 Comments leave one →
  1. Hilary permalink
    February 20, 2009 4:41 pm

    Great detail – I was riveted! Excuse the pun, but I seriously enjoyed reading about it. Now if I could only hear/see it. Nice pics too. Enjoy your next track day!

  2. February 23, 2009 11:15 am

    hey. I weld like that! looks like chicken crap. But great job on the muffler. Hope it holds together for the next race.

    Reminds me of the kawasaki project you helped me with back in High School. However that muffler had no baffles at all – it was just a tube that shot flames and smoke out.

    • spotcom permalink*
      February 23, 2009 8:51 pm

      There’s nothing wrong with pipes and flames! (Who needs mufflers… LOL)

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