Muffler Repack Project

How To Dismantle and Repack A Mild Steel Exhaust Sports Muffler.

Motor cycle enthusiasts have long had the luxury of re-packable sports mufflers. But it appears that re-pack sports mufflers for the car enthusiast are not so common, or readily available… at a reasonable price.

Over the past few months the writer has been investigating the possibility of sourcing a stainless steel re-pack muffler for the Lotus elan S2.

After several fruitless searches, one or two companies offered to custom build a re-packable stainless steel muffler to suit the elan, BUT, OMG the price!! Ridiculous to say the least… so the interest kind of waned…

But the re-pack thought never left my mind, and it was still piquing my curiosity, because the Aussie made mild steel Red Back exhaust muffler fitted on the S2 elan had become very raspy and noisy, quite annoying while driving around town and when on a long trip… and certainly not enjoyed by the wife as a passenger.

At the end of this article you can watch a video under varying driving conditions showing the different exhaust noise at different rev ranges. 

While surfing the web, we stumbled across an interesting post on the lotuselan.net forum about re-packing a “sealed” stainless muffler fitted to an elan, so naturally we read and book marked that page as a point of reference, because it seems the elan poster had gone down the same road  for the very same reason… where the muffler had become ineffective, I.E. far to loud.

We then wondered, was it possible to cut, shut and convert a factory made mild steel muffler to a re-pack design…Would it still work OK?  Or would it fall apart when cut open? What will we find inside when it is finally opened…

With the exhaust system still on the car, we tapped the underneath of the muffler with a screw driver handle, it sounded hollow and tinny as though the packing had disintegrated and disappeared out of the rear tail pipe.

It was time to get to work and cut the old muffler open…We had nothing to lose.

Understand that the muffler being converted was en everyday run of the mill Australian Made Red Back mild steel straight through sports Muffler – this brand of muffler (And many others) during manufacture are produced with thick rolled joining seams along one side of the barrel, and on each end… they are a bit on the ugly side, but then, that’s mass production for you.

I really admire the look and style of a hand built stainless steel re-pack muffler, and if all goes well with this project, there will be another exhaust project happening in the near future – IE, building a re-packable design stainless steel muffler for the elan — but for the time being, we have the original Red-Back sports muffler to work on.

The first thing to consider with a muffler repack project was to source a suitable repacking material.

A search on the net found a local web site site called Australian Thermal Technologies, distributors for a product called Acoustafil PTX Infil Muffler Filler or packing, and according to the size muffler on the elan, we required a piece of material 400mm wide, by 1 Metre long – The price for the Acoustafil at the time of the project was $54.50AU.

I am happy to give these guys a free plug.
Australian Thermal Technologies – 44 Castle Circuit Seaforth NSW Aust – Mob: 0403753944. The owner John is a really helpful bloke.

Acoustafil is a specially formulated cutting edge muffler repacking material.

On closer examination, the material is more like a blanket in its construction, having several lines of stitching spaced about 30mm apart along it’s length, which helps to keep it bound together, the outer edges are also sewn or selvidged, which is of great advantage when packing the muffler as we will explain later.

Acoustafil does not seem to have any bad fibre loss during handling either, so it wont, or should not irritate while being handled. But it’s probably still wise to wear a face mask, just to keep the OHS police people happy.

A Warning To DIY Muffler Cutters – From here on in, the job gets stinking filthy – Inside of every old muffler is a very large amount of burnt original packing material dust and old packing fibre, along with a ton of black as the Ace of spades carbon particles – Keep Your mask on for the cutting – separation and cleaning of the muffler – You have been warned.

Because we don’t normally ever cut open old mufflers like the Red Back Muffler, we were not exactly sure where to cut the outer skin. So we decided not to cut to close to the end.

The cut off blade mounted in the angle grinder makes quick work of the thin outer metal muffler shell. The cut off blade is not large enough to cut the inner tube as well, but the hacksaw made short work of it, as shown below.

The quickest, easiest way to cut the muffler is to use a hand held 4″ angle grinder fitted with a 1mm abrasive cut-off blade, the cut lines are carefully laid out on the outside of the muffler, required for accurate cutting with the angle grinder, it is important to cut neat and square, cut the outer shell with angle grinder right around the perimeter, then use a hacksaw fitted with a new blade to cut the inner pipe.

Clamp the muffler and or exhaust system while cutting to avoid accidents. (And yes Please WEAR your eye protection safety glasses).

When the muffler was cut open, the old packing was found to be very loose and it had diminished considerably, so is it any wonder that it was acting as an echo chamber and not as a proper muffler.

After the cutting operation is complete, make sure to remove all of the jagged edges and swarf left from the cutting action, a dremel, die grinder, or half round hand file will do the job.

The muffler has been in service for about six years, and to be honest, the sound became louder as it approached the two year mark, and it is easy to see why from the look of the old packing material.

It was a filthy job removing the old packing, which was done out in the open with the wind blowing the crap and dust away.

The muffler and the end cap, with old packing removed and the muffler cleaned with a wire brush, de-greaser, high pressure washed, then propped vertically against the outside workshop wall to drain and dry out in the hot Aussie sun.

Make special note of the extension piece of tube (Photo Above LHS) which has been welded to the inner pipe of the main muffler body, the extension piece is designed to slip into the end cap pipe to secure and hold the pipe when the parts have been assembled.

The next few photographs are going to illustrate how the muffler is converted into a Re-Packable muffler, which will also mean that it could be taken apart again in the future to re-pack again.

The photo above illustrates the inner sheet metal (0.9mm- 0354″) Cold Rolled sheet seal flange being rolled into an oval shape… is best formed with sheet metal rollers, but with a bit of manual work, could be formed around a short length of water pipe of the correct diameter.

The sheet metal rollers shown above are nothing fancy… they are about one hundred years old!!

The two muffler parts above is where most of the work is involved. Note the notches cut into the flange edge of the end cap, this is a bit of a cheat method for fixing the rolled inner seal flange to the end cap… When the inner sheet fits snugly into the end cap it is spot welded.

Once the tack welds (Which are not the neatest by the way) have been cleaned up, the end cap can be trial assembled into the muffler body to make sure they will actually slide together.

At this stage it is essential to trial fit the end cap to the muffler body, making sure that the inner seal sleeve does in fact slide into the body of the muffler, if the fit is to tight rework the inner metal sleeve until a nice sliding fit is achieved.

If assembly problems arise later after the muffler has been packed, it will become frustrating when trying to assemble and seal it all up.

If the fit as acceptable and the end cap can be easily pushed in, and pulled out again, and the two parts mate up neatly, then the next step is to drill three or four holes for 1/8″ sealed pop rivets at an even spacing on each side of the muffler body. (See Later)

NOTE: Sealed end or capped pop rivets must be used for final assembly and to hold it all together. (See later).

Now the fun begins, looking at the amount of filler material and what looks to be a small space in the muffler body, the thought is that it wont all go in… And what is the best way to get the material into the muffler?

First off, cut and roll a core of manilla folder card board, the core ID needs to be slightly larger the the internal muffler pipe. With this oval muffler, we rolled about 2.5 to 3 layers onto the cardboard core, then cut the remainder off with a pair of sharp scissors, and put the off cut aside for now.

Roll the Acoustafil carefully onto the card board tube, then gently push and work the packing into the muffler body, make sure the acoustafil goes all the way into the muffler, a portion will protrude, but the end cap will cover that when assembled.

Once the packing is pushed fully home, reach in and grab the cardboard tube with your fingers and gently pull it out, then discard, because you wont need it again.

The next step is to cut several strips from the piece of Acoustafil that was left over, the strips will vary from 80mm to 100 wide, and may have to as narrow as 60mm. These strips are to pushed into each side or narrow part of the oval shaped muffler.

At the beginning of this article when describing the Acoustafil, mention was made of the selvedge edge, well, the sewn edge is very handy when inserting into the muffler, because a a stout piece of wire with a hook bent on one end can be used to push each strip the full length into the muffler…. easy peasy, lemon squeasy, as they say.

Making good progress, we are into the final stages of the muffler re-pack project, all we need to do is to slide the end cap and push it fully into the main muffler body and we are pretty much done. Take note of the guide tube, which is just a short length of smaller Dia exhaust tube, and the sole purpose being to stop any of the packing material to becoming snagged between the inner pipes when they slide together, that is all.

Carefully push the end cap into the muffler body, it should be a firm hand push sliding fit. Make sure to use high temperature RTV sealant between the muffler body and the inner sealing flange of the end cap. Blue or red RTV will be fine.

It is essential to use only sealed head pop rivets, as they will not allow any leakage, the job is almost done.

The muffler is now repacked, re-sealed, re-painted and ready to re-install back into the car, the job as it turned out was not all that difficult to do.

Of course we still have the test drive to do, and cant wait to do that just to see what the difference is going to be like.

My tip is that the noise level out on the open road will be less, but we should still have a nice round and full sounding exhaust note under hard throttle – We will learn the truth after the re-install of the muffler and exhaust system.

OK, here we are looking underneath the rear of an S2 elan… different from standard isn’t it. Yes, very different. This is the system we have used for many years to support the muffler and exhaust, and has proved to be excellent.

The boot floor was remodelled many years ago to accommodate the long sports muffler. It previously had the ridiculous S2 exhaust pipe and twin side by side configuration muffler setup, but after losing the exhaust two or three times, it was time for a redesign, and this what it now consists of.

The flexible rubber mounts are Mini 850 exhaust hangers and they work like a charm – The brackets etc, are the product of the writers hand fabrication work.

If you are elan purist, you wont like it – but that’s OK, your allowed to, but I will take solid reliability and ease of installation over crappy exhaust design any day.

So there you have it fellow Lotus owners, that is how an ordinary Aussie made Red Back mild steel muffler was converted to a fully re-packable muffler.

And now it’s time for an actual road test… So we did an open road test with the hard top on, and another run with an open cockpit, and see what the difference is… Below is a GoPro video/audio recording so that you can listen to the exhaust note.
There is no recording before we did the work…but believe me it was loud.

The exhaust sound as it stands now, still provides the typical twin cam Lotus wail under hard throttle but goes fairly quiet on a steady throttle setting, I think I can put up with this for now.