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Did you know that most pipe manufacturers expect you to repack the mufflers from time to time? Didn't think so. Because these mufflers use fiberglass (or something similar) as a packing material while stock systems employ solid steel (or titanium) baffles, they don't last forever like the OEM pieces. (In fact, even the original mufflers will degrade over time, with the moisture from combustion eventually corroding the internals with broken baffles being the most common result.)
Fortunately, changing the packing material is nothing to sweat. Check with the muffler manufacturer; most offer special repacking kits that include everything you need. This one, from Two Brothers Racing ($19.98; 800/211-2767 or www.twobros.com), includes the repacking material plus replacement rivets and even the correct drill bit for removing the old rivets. In addition, you'll need an electric drill and a "pop" rivet gun. (See Tool Crib, page 93, for our recommendations on riveting tools.)
Remove the muffler from the bike and place it on a clean surface. Follow the directions for your muffler, but generally you will need to gain access to the packing by separating the muffler body from the inlet end cap (1). Insert the drill bit--this is a #30--into the drill and fit a drill stop if you have one. If you don't have one, wrap tape around the bit (2) approximately 10mm from the tip. This will prevent you from drilling too far into the muffler body.
Carefully drill out the rivets (3). Usually, the rivet heads will pop off first, leaving a bit of the rivet body still in the hole (4), but don't worry about that. You can come back later and remove the rest of the rivet. If there's a retaining strap (as on this Two Brothers Racing pipe), remove it.
Sometimes the end caps are a tight fit into the muffler body, so some gentle persuasion with a plastic-head hammer may be in order (5). Wearing gloves, gently pull the end cap from the muffler body (6). If you get fiberglass strands on your skin you'll be a very unhappy camper, so be sure to wear gloves and consider a long-sleeve shirt, too. Remove the packing material and discard.
Tightly wrap the new mat around the core (7) and test-fit the wrap in the muffler. Most kits come with more material than you can use, so don't be alarmed if there's excess. Secure the material with strips of masking tape (8). Yes, the tape will eventually burn off, but you really want the material held tight to the core as you reassemble the muffler. You may need to trim excess mat from the end of the muffler with a razor blade (9).
Before you reassemble the muffler, check the rivet holes in the sleeve and end cap for burrs and cracks, and shake out the old bits of rivet. Insert the new rivets and pull them (10). Check to make sure the rivet head is flat with the surface (11). Wipe the outside of the muffler with mineral spirits to keep the oil from your hands from etching the metal and don't be concerned if the pipe smokes for the first few miles; that's normal. Now, doesn't that sound better?