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diy_a_muffler [2009/10/20 15:44] (current) created
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 +====== Making your own Muffler/ slip on from scratch ======
 +I started with a piece of 4" aluminum tubing which I squished between
 +two boards in the vise to a pleasing-looking oval.  Then I traced the
 +ends of the oval onto 1/2" 6061 aluminum stock and cut the end caps on
 +the band saw.  A little work with the disk sander and the end caps
 +matched the oval canister quite well.
 +Then (the scary part) I mounted my router in the router table with a
 +carbide cutter.  I fastened a piece of wood to the fence and advanced it
 +into the cutter so the cutter was finally exposed by about .1", with a
 +height of about 3/8".  I was then able to cut the rabbet in the end
 +caps, depth about .1" and height 3/8".  This rabbet allowed the outside
 +of the can to line up flush with the outer edge of the end caps.  Next
 +time I think I'll see about a speed control for the router.
 +Then I bored holes in the end caps to clear the 1.5" stainless tubing
 +used for the tail piece and the inlet spigot, inserted the end caps into
 +the canister and drilled the mounting holes for the caps.
 +I made two steel disks with center hole to match the OD of the tailpipe
 +and inlet spigot and welded them to the pipes, then drilled them and
 +tapped matching blind holes in the end caps.  I left about an inch of
 +each pipe extending past the disks inside the can.
 +I went down to the local muffler shop and had them cut me a piece of
 +1.5" steel tailpipe just short of the distance between the end caps on
 +the inside, then bell the ends for an easy slip fit over the spigot ends.
 +I wasn't enthusiastic about drilling 1000 or 1200 holes in the baffle
 +pipe, and the muffler shop's owner (a hardcore motorcyclist and former
 +racer) suggested I cut slits instead.
 +It worked beautifully.  With a carbide blade in my radial arm saw, I
 +adjusted the blade'​s height to about 1.3" above the table, then put the
 +baffle pipe in place and drew the blade across it making slits about an
 +inch long or so.  Twenty slits down the length, then rotate the pipe 120
 +degrees, twenty more, then rotate and cut the remaining 20 slits.
 +This exercise probably took about 20 minutes.  I'd have been drilling
 +for hours.
 +I took a punch and louvered the leading edge of each slit, but I don't
 +really think it made much difference.  Easy enough to do, though.
 +The baffle pipe was now a nice slip fit on the spigot ends inside the can.
 +I bought some fiberglass muffler packing from Cycle Gear (the 4 stroke
 +stuff, which is much denser and holds up better), wrapped it around the
 +baffle pipe and assembled the muffler.
 +A couple of brackets and Bob was my uncle.
 +Here'​s ​ picture:
 +This BSA single is painfully loud with a straight pipe but quite
 +civilized with this muffler.  I'd been using a motocross Supertrapp, and
 +when I changed to this one the sound level went down about 20db.  And I
 +had to increase the main jet three steps.  With a nice increase in power.
 +So the muffler is quieter and makes more power.  Just what I had in mind...
 +==== Written & designed by Jim Stewart ====
diy_a_muffler.txt · Last modified: 2009/10/20 15:44 by