Nobody likes a noisy bike. Not only are they obnoxious to the ear, but bikes with poorly-packed or blown-out silencers are robbed of precious horsepower as their finely tuned exhaust systems cease to work at peak efficiency. But what if, your bike sounds like a bee in a biscuit tin, and no longer performs like it used to. Then it's time to learn how to repack your exhaust.
Remove the exhaust system from the motorcycle. This is easy, if you take a few thinks into account. All the muffler bolts get very hot. The constant expanding and contracting can cause fasteners fatigue and will dry out the threads. Spray some penetrating spray on the bolts before removing them. Dig all the mud and dirt out of the thread and fasteners before you start, while taking note of any gaskets you might need to replace as you disassemble.
For the second step you need to separate the silencer. Have a look at the muffler and work out how it comes apart before you start attacking it with a hammer. It should have either rivets or screws at both ends. When you have removed what you think are the right ones, hold either the muffler or the intermediate pipe in a vice and try tapping (careful) with a nylon hammer to see if it will budge. Often there's some silicone you to break before it will begin to move.
When you worked out how to get the muffler can open you can proceed in cleaning the core. The small holes in the perforated core need to be clean so the packing material can do its job, and there's a few away to do it. If you have a blowtorch, it's easy to burn the carbon out of the holes. As an added bonus, if it's a two-stroke, you get to smell the oil burning. Castrol R is the best. When it's hot enough, bang the core with a piece of wood and all the hot, dry carbon will fall off, but be careful not to dent it. Alternative, you can use a wire brush and a drill bit, but playing with fire is much more fun.
After the core is well cooled down and crispy clean you can prep for repacking. Inspect the body, core, end-caps intermediate pipe and fasteners. If the core or body is cracked, have it welded-up. Repair any damaged threads. Replace fasteners with stainless steel ones.
When everything checks out fine, you can start wrapping the packing. This stage is different for two-strokes and four-strokes. Because of the heat and naked flames that a four-stroke generates in the muffler, glass-fiber packing material won't last for more than a few hours. To counter this, first wrap the core in a single layer of stainless steel wool to protect the glass strands. Then use a long-strand fiberglass packing material you can get from some Do-it-yourself shops. We buy a 30m, 1.8m wide roll of glass packing for a couple of thousand Baht, which lasts for years. Some locally construction DIY shops sell fiberglass in smaller bundles of packing.
When refitting it to the can, use packing tape to keep all the packing in one easy-to-fit piece. We tend to pack tightly, as it lasts well and makes good power, but the tighter the pack the heavier the pipe. Slide the core into the can gently, twisting as you go. Getting the core to line up with the end-can be a bit tricky. Sometimes a wooden dowel (broom handle) is needed to line it all up. Reseal with high-temp silicon sealer at the ends so it's airtight, and then line up all the bolt-holes.
The last step is screwing it together. Mufflers tend to shake themselves to bits, so use some thread-lock to keep it all together. Replace and rivets you have drilled out with stainless steel once or use some really good stainless steel self tappers. It you refit with rivets do one at a time, but just squeeze the trigger enough to make the rivet hold, without breaking the end off. Then do the next one. Pretty soon you end up with a porcupine looking thing. Only when they are all in should you finish off the job by pulling the rivets up fully and breaking off the ends.More about the Exhaust Muffler Packing Materials.