Making my own muffler and need some advice

I am the very cheap owner of an 08 KLR650 and also a welder. I have shears, plate rollers, bending brakes and anything you can imagine at my disposal. On my commute home tonight I started thinking about how basic and expensive aftermarket exhaust's are. My thoughts were to use a thin walled stainless pipe as the outer shell. Make an inch and a half perforated inner pipe from stainless. Wrap that with a layer of stainless steel wool and then the rest can be a fire retardant material. At work I use a fire blanket called Refracail that takes a lot of heat. The front inlet cover can be welded to the perforated inner sleeve and riveted to the outer shell. The exhaust end can be slipped inside the outer shell and riveted also. I think it would be about $400 cheaper then an aftermarket exhaust and something I can be proud of. Mostly pride in how cheap I am. How long should I make the thing? It needs to be short enough to........umm how should I put this...... Leave work with it without looking like I'm leaving with a muffler? Not that I am a crook, it is all going to be scrap stuff out of scrap bins. But the less attention I get is for the best. Any input on this would be great and appreciated.:dllama

if it's going to be 400 bucks and your are making it out of scrap go get a used one off of Ebay for less then 250. At no point do i see 400 bucks for a muffler cheep. Now if you are just wanting to do it because you can and what to say you built it, go for it, the only difference i would do is buy 4-stroke packing instead of just something you have laying around, is cheep and it's what is meant to be in there.

have fun and good luck. and take pictures.

He did say $400 cheaper than an aftermarket exhaust. So I'd say he's up for $100?
Sounds like a good project for the money.

It would cost me next to nothing but my own precious time. I drew up a quick draft just to get the basics in order. The shell is drawn at 12" long and 4" in diameter. The inner pipe is at 1.5" should be fairly simple with hardest part being the location of material for the perforated inner pipe.

On some of the country roads I ride there are stop signs that have been blasted by shot guns...just sayin'

This isn't exatly DIY, but a whole lot easier and not horribly expensive at $11/ft or so. I built an exhaust tip for a XR650 with a smaller diameter piece of this and it is good quality stuff.

http://www.baronscustom.com/catalog...ml?PHPSESSID=b470fdf99b00a433e798d0b52c55a74b

yeah read that wrong. and a drill press a small sharp bit and some time you can make the inner piece. we did it once for a 2-stroke muffler. And again I say use the right packing. you'll only be out 30 or so bucks. I think


Edit. here's the cheep kind 9 bucks. http://www.rockymountainatvmc.com/p/44/54/207/905/-/4653/FMF-4-Stroke-Silencer-Packing

and here's the pricy stuff. http://www.rockymountainatvmc.com/p...-Premier-Multi-Layer-4-Stroke-Muffler-Packing

I've used the cheaper one a few times. it works.

I'm at work now and found some perforated aluminum in a dumpster. About 14x12. Perfect size. Now to decide whether to use all stainless for the shell and ends or lighter aluminum. Aluminum is a lot easier to work with but turns dull. Whatcha think?

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Also what size is the header pipe? I'm not near my bike tonight and forgot to check. I keep thinking 1.5" but not sure.

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Never dull will keep aluminum shiny.

Shiny/KLR

I'd look for a baffle design that doesn't need repacking. How often do you want to replace your bike's tampon?

As long as you don't have to do maintenance on your muffler (!?!), why not weld the ends? There are a lot of threads about rivets/screws coming out...

A spark arrestor might get you off a Ranger's hook one day...a straight-through Cherry Bomb won't.

I also need to find the mid pipe that runs from the aftermarket muffler to the stock header. Cheapness is key. Any suggestions?

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I can show you the guts of an FMF Powerline muffler if you like. They are mechanically baffled and looks like it will flow well (compared to a stock muffler)

Any exhaust shop will be able to do it, except the tube wall thickness will be about twice as thick as the stuff used for after market pipes. Here in Australia, stainless tubing is about 30 bucks/metre and a local exhaust shop charges 5 bucks for each bend, flare, reduce etc.

I'd like to see that.


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No worries. I will get some photos and post them later today.

Alright here's what I have so far. No pics yet but will after. I have the 4" outer shell made up and had the 2 end plates made out of 1/8" alum plate. 4.25 in diameter and an 1.875 hole in the centers for the inlet and outlets. I have my short end pipes all cut to length a need to weld them to the end plates. The inner rings the rivet the ends to the shell are made and waiting to weld. I also made the inner baffle with perforated alum. That was a feat to undertake. I had no way to roll the mesh to such a small diameter so I took a 1.875" od pipe and cut an 1/8" groove all the way down the center of it leaving about an inch uncut on each end. Then I slipped the 12" long perforated metal into the slot about a 1/2" and pushed on the pipe as I rolled the plate around it tightly. I rolled it until it was about an inch past the starting point then clamped it. I then used a cutoff wheel and cut lengthwise down the pipe where the mesh overlapped. Once it was cut I got rid of the extra and clamped the mesh around the pipe with hose clamps to hold the diameter. I will then tack the mesh to itself and slip the pipe out. Stay tuned. Once I get it off the property I can take some pictures of it before assembly.

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I think it's a big mistake to underestimate the amount of heat that will be applied to the front cap of the muffler. I think aluminum is not the best choice for that.

I have experienced how the rivets can cut through the exhaust shell and open up the exhaust from the header side. Lots of heat and backpressure.

For a DIY, I'd weld a stainless front cap to the stainless shell. I'd do my best to use a long-lasting dampening material. I've used stainless steel pot scrubbers with pretty good success. They don't insulate heat well, but they last way longer than fiberglass. If I were building an exhaust, I'd definitely put in a spark arrestor. Use rivets (or bolts, preferred) to hold the end cap on for periodic checks and re-packing.

Go to the junk yard. get a good stainless steel muffler. Make it to fit your bike

Wouldn't the exhaust gas heat melt aluminium?

Anyway, here are the FMF Powerline photos. It has to be shortened by a couple of inches to better fit my 90 model RS, which is why it's in this condition This version fits a Suzuki 400 quad and after looking at a few photos, it appears they use the same standard size muffler and change the mid pipe to fit all the models they are made for. (Polaris 800 looks the same size as a Yamaha 250)

Outlet end. Hole is 1.88" dia. Inner slotted pipe is 2.5" dia. There is an end cap which reduces the hole to 1.8" and has 3 threaded holes for attaching the end baffle, spark arrestor and outlet cap.



The inner pipe is blocked in the middle and there is stainless expanded mesh around that which squashes the black material against the outer case. Presumably it acts as a heat shield.



Close up of one half of the inner slotted tube



Inlet end.



Material covering, which was held in place by masking tape!



End baffle / restrictor thing for the outlet. 1.5" dia with 2 deep opposing slots and the deflector plate welded into the end.





Overall length is 16.5 inches, height is 4.7" and width is 3.4"

Cheers,
David.