Muffler/Expansion Chamber - Making One

No Problem

I daresay the patent office would giggle...

I had a thought - happens, in spite of swigs.

Instead of test ride, I will put engine on bike, get it running hot at idle and just push the silicone hose over the exhaust pipe to denote decibel change, if any, and if I can tell. (I have one bad ear and one that is still suffering from flu symptoms.) And, will not be tempted go for a spin on the winter road sand/salt laying around waiting to kiss me bum and get another "farging" cold because I was a stupid "icehole." - quotes from Johnny Dangerously.

That way, will have early answer and then watch basketball and swig.

Will also note if silicone hose can take the heat at the exhaust port...may be easier to clamp a hose on the port than the 3/6 elbow now using, but, even so, that change would alter current connections to keep muffler under engine, so will not alter this version. I already heated it a number of times.

I also will have to determine if the thing creates an oil drip problem. I do not want to pollute any more than I am and do not want oil dripping on anything under engine that might be hanging on the aluminum bar stock rack I will be installing on that side to match the one on the port side...see pic of current rack.

The engine hangs over all on the starboard side, and I recently noted a very slight bit of oil on the engine cage, which may be from gas mix that spilled etc. No oil on me bananas...

Keeping Up Suspense

I decided to go with copper mesh as sound absorber. I do not believe the can will get hot enough to melt the silver solder or mesh.

Copper mesh is way easier to locate than SS mesh and cheaper. Seems it is used as rodent protection.

Using "loquin's" advice on how to construct the baffles - the "Swedish Muffler" construction, abbreviated. Will archive with pics.

But, unfortunately, looks as though we are going to get 5 inches of snow and cool weather (UGH!) for a few more days, so the test will have to wait and the garden prep continues. Yard covered with trimmed tree branches...

Looks like we're working on them about the same time then. I've got aluminum mesh as the inner tube, and fiberglass mesh around that.

Using 1.5" EMT conduit for the outer shell, with half inch EMT on the inflow and outflow.

The silicone tubing from Daves Motors seems to be holding up fine on the last attempt. (That last attempt's still on, but hasn't lived up to my expectations.)

If I just hadn't ran out of Oxy on the torch, it'd be finished now!

Muffler Construction Pics

I put the muffler together and attached it to the running motor and it did reduce the sound sufficiently to make it worth it, at least to this point. Let's say the exhaust was tempered to a low mutter instead of a high putter. It adds a pound or so to the overall weight.

Ran for half hour or so. Rig was not hot. Some exhasut stillexcapes from very small opening where pipe and screen are attached to stock can, and sound as well.

Sooooooooooo, It is worth it?

NO! The difference in sound vs the work and having more stuff to worry about makes it a dubious proposition. Regardless, below is the process. Simple is best...Nevertheless, am going to run it over the next few days at speed with muffler, then with just long hose, then stock.

I suspect what the outcome may be...Live and learn.

As indicated, materials from copper plumbing pipe. See previous pics. Silver solder. Black high temp hose from Dave's. Vise, torch, large pliers, heavy gloves, number of appropriately sized ss hose clamps.

I obtained copper mesh from here: http://www.brewhaus.com/ $13 scoots. It is used for condensing booze in stills. Lots of mesh. Use excess to keep rodents etc from house or sell to another muffler nut.


The system is assembled so there is about 1/2 inch of pipe extending from one end and 6 to eight from other tail end, which can be trimmed later, if necessary. Review pics to get better idea.

1.) Center pipe is measured for can area slits to permit exhaust to be muffled with cutting wheel used to open slits into pipe at one end, length of the enlarged portion or can. Remove flashing etc; test to make sure the two reducers will move over pipe.

2.) Clean all solder surfaces, flux - I used liquid flux.

3.) Place wood dowel into core pipe with a bit extending above. Will keep mesh from crushing copper inside chamber when stuffing.

4.) Do by sections. Position one end cap in place and cut off about two inches of mesh to wrap around core. Pack space between core and outer wall with mesh. Keep adding mesh until even with top, tight, but clear edge for 1/16 so connector will fit. Can all connections with silver solder solder last.

5.) Add middle connector and mesh tightly, right to top, but keep mesh from outer edge a bit for end cap fit.

6.) I did not take pics of this step, and should have. Place a piece of copper pipe into the end cap, so it protrudes from both ends. This will serve as dowel and guide for installing last piece.

Stuff the end cap as before, allowing say 1/8 inch to 1/4 inch of mesh to protrude, so it will go into center piece when pushed into place.

7.) Place the copper pipe/end-piece over dowel and push or hammer into place. (I used the over sized assembled "T" in pics to drive the pieces together. Adjust the main piece in the vise so the main piece is supported in position from bottom, so it will not move when end piece is positioned.

When in place, with about 1/16 overlap, sections can be soldered.

All that is left to do is attach hoses and hang.

Will show that portion next. It might be possible to place large metal retainer for bolt surface without removing the cage, otherwise, protective lower engine cover must is removed by removing two screws on either side and unsnapping from top section.

I plan to use large washer or metal plate-bracket to anchor to inside cage to spread out the pressure and use a bike bracket or metal strip, connected to muffler via hose clamp, angling the exhaust as desired - Tanaka engine cage is angled with rear down, so its angle must be reversed by the bending or aligning the hanging bracket for horizontal position straight to rear. Of course, one can do this with a 45 degree elbow in tail pipe section, but adds weight and extra work.

Pic of Center Tube

I thought I had posted this one but not so.

The center tube, surrounded by the mesh.

This is one section of the slits, I did two sections, complete length of the "can."

The openings require a dowel, when the mesh is installed, so the mesh retains its shape, does not occlude the main channel or crush the copper sides ofthe strips and keep main thrust of exhaust gas moving direct...

Got mine finished yesterday, also. Will post actual construction photos in the next couple of days.

It is the classic "Swiss silencer" approach, used with airplanes, as Switzerland has VERY strict anti-noise pollution laws regarding airplanes and airport zones.

Essentially, the swiss silencer is a long aluminum tube. Inside this is a roll of fiberglass cloth. (Used in fiberglass airplane or boat hulls) Since I'm looking for a lower-cost solution, I'm initially trying it with fiberglass window/door screen. Inside that is a tube made of stainless steel screen/wire cloth. Since stainless steel screen is hard to get, and is expensive, and the only places I've found that carry it have a minimum order that would be enough to make 20 or 30 tubes for bike mufflers, I decided to use aluminum window screen for the inner tube of the silencer. If it works out, Fine. If it breaks down quickly, (but, the muffler works) then we can move to a steel or stainless version.

For the main body, I used 1.5 Inch thin-wall EMT electrical conduit. Inflow and outflow tubes are .5 inch EMT conduit.

The wire/fiberglass screen dimensions are based on a 12 inch long outer shell. Per the swiss silencer article, the silencers for small aircraft are 1.2 to 1.5 meters (4 to 5 feet) in length! If we assume that the aircraft use a 2 inch exhaust, scaling this same length down to a 1/2 inch exhaust yields 12.5 to 16.5 inches. The metal screen is the same length as the outer shell, The fiberglass screen is 3/4 inch less than the length of the outer shell.

Cut the aluminum/stainless screen to 12 inches by 4 inches. Fold the long edges 180 degrees and flatten, using a ruler as a guide, approximately 1/4 inch from the edge. This is to protect your fingers from the sharp cut wires.

Roll the aluminum screen into a tube shape. wrap it around a 12 inch long section of 1/2 in conduit. Using thin flexible steel wire "sew" the outer edge of the screen in place to form the tube. With the conduit still in place, loosely roll an 11-1/4 inch strip of fiberglass screen around the inner mesh tube until you have an inner core which will just slip into the outer shell. I found that an 84 inch screen-door replacement screen was just the right length. (so, a 3' by 84 inch screen door replacement roll will make three, 12 inch silencers.) Temporarily place a rubber band around the inner core assembly and set it aside.

The ends caps are the challenge. As it turns out, sticks of conduit can be joined together with either compression fittings, or with a steel slip coupling which uses set screws to hold it in place. An example slip coupling is shown in the first pic, below. Note the conduit stop that is pressed around the fitting - you will cut the fitting in half along this stop. Be sure to use a steel coupling, and not a cast aluminum or zinc coupling. Buy three 1-1/4 inch steel hole plug (ref second pic below), and drill an approximate 5/8 in hole the center of the plugs. (Note that a 1-1/4 inch hole plug just fits inside a 1-1/5 inch EMT slip coupling! This is because the hole plugs are designed to work with thick-wall, threaded conduit.) The holes should be drilled in all three of them, but, one will be used as a centering jig. The holes should allow the inflow/outflow tube to just slip through. Next, insert one of the hole plugs into the cut end of one half of the slip coupling, and braze/weld the hole plug into place. (tack one side, then the other, as the plug will warp up otherwise.) Repeat for the second half of the slip coupling.

Next, slip the third hole plug into the open end of one of the slip coupling halves, but do NOT weld/braze this one. Insert the inflow tube through the welded end cap, and on through the centering jig, about 3/4 inch. Now, weld/braze the inflow tube to the previously welded cap. Be SURE not to weld to the centering jig. As before, tack two sides before completing the weld. Remove the Centering jig, and repeat with the second half of the slip coupling and the outflow tube.

Now, it's time for final assembly. Remove the rubber band, and slip the screen core assembly inside the 1.5 inch outer shell. Carefully insert the inflow tube, which projects out beyond the end cap, inside the wire cloth and slip the inflow cap fully into place. Securely tighten the two set screws. After I test the unit, I plan on adding a pop-rivet to the opposite side of the silencer to make sure it won't come off. Then, if I ever need to replace the core, it will be easy to drill out. Repeat for the outflow cap assembly. And, you're done.

You should be able to use conduit hangers, or hose clamps to support the silencer. Ref the third pic, below.

I'll be testing the silencer soon, and will report back on it's effectiveness.

My Final Words on Project

Not worth it!

Simple is best...change is insignificant. Perhaps connecting directly to engine port, without the stock box, might produce improvement, but is likely too much trouble also.

After all, these are simply motored bicycles, not race machines, etc.

Simple is best.

Amen for this boyo!

AHEM... If it ain't broke, don't fix it especially applies to the exhaust. If you're not trying to make it quieter, don't try it. If you're not pushing 4+hp, don't try it. You will be sadly disappointed with the time you've wasted.

Hold on there, cowboy!

I temporarily hooked mine up last night. Even with the end of the silencer pointed right at me, it reduced noise levels significantly (I don't think it was cut in half, but it is significantly less,) and the tone is definitely lowered. It seems like most of the high frequency stuff is just gone. I AM going to order some of the fiberglass cloth and try it as well - I believe it will help even more. Now, with the sound levels reduced, I did notice that there was a fair amount of sound coming through the walls of the existing muffler on the engine. I don't know if anything can be done about that, though...

I believe your silencer had two issues, Hive.

• First, I just don't think it was long enough. On the light/ultralight aircraft, they're 4-5 feet long. If you keep the same relative dimensions based on exhaust diameter, that would be from 12.5 to 16 inches in length. At 12 inches in length, mine could actually stand being a little longer.
• Second, the copper mesh you used can't absorb the sound energy - the individual strands of copper are too thick (and thus too rigid.) In the swiss silencer, the woven metal screen isn't used for silencing - it's just used used to form the exhaust airway (and keep it open), and to retain the fiberglass 'cloth' which actually deadens the sound. (Since the fiberglass is very flexible, and "loosely wrapped," the individual fibers can vibrate, and as they do, they absorb sound energy)

One thing I noticed on the swiss silencer web-site is that the silencer is open at both ends. This would cause the sound that is left to be diffused more, rather than being focused again at the outflow of the silencer. That's another area for future investigation. I believe after trying the silencer with fiberglass cloth replacing the fiberglass window screen, I'll drill a series of small holes around the perimeter of both the end caps.

My Failure

Loquin's observations are very likely spot-on.

I chose not to have lots of stuff sticking out etc, and just wanted to see if it would work. It does take out some high sounds, but not really so much that it is worth it and to keep it on the motor. More stuff to fail...

As to using glass in stead of the mesh. That is also try. I have lots glass around and may figure out something for next year.

For the smaller T33s and similar motors, like Sparky suggests, the higher cc motors are the ones that need the quieting.

Back to golf and yard work...