"Homebuilt" expansion chamber

Discussion in '2 smokers' started by dorkpunch, Jan 28, 2011.

  1. Valleyrider

    Valleyrider I Survived The '60s

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    #21
  2. svejkovat

    svejkovat Been here awhile

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    On the low tech, easy as can be, side I offer the baseball bat muffler. The local scrap metal yard charged me about three bucks per little league bat for a half a dozen of them one day. Figgur'd the tapered cone would come in handy for some welding project down the road. Years later I needed a muffler replacement on my Puch moped and spied the poor little buggers in the corner of the shop trying to look inconspicuous. I cut a couple of them up on a miter saw and welded them up. Took all of about two hours. (cutting aluminum on a standard compound miter saw with a non-ferrous blade... one more of life's simple pleasures!)

    [​IMG]

    They're little league 2.25 dia bats. Adult league 2.75 diam would have been better perhaps, but they weren't in the cards that day.... so there. The end actually does taper but is hidden on one more bat end which contains the silencer/packing

    It was a noticeable improvement on the stock job, according to my seat-o-the-pants dyno and about +5mph top speed (thrilling on a 49cc moped). But most of the fun was in just repurposing something for another job.... one of my favorite hobbiies.
    #22
  3. dorkpunch

    dorkpunch Oops...

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    Thats pretty slick! I love finding new uses for old junk. Have to keep that one in mind.

    Back to my build... Microbraking. I stopped in at a local metal shop to visit with the owner about a couple of things. We had him give us a quote for installing a new furnace and he had given me a couple of ideas of things to do in my class. Turns out he didnt have a way to roll cones either, and his slip roll was even bigger than mine, but he introduced me to "microbraking" Basically, you can roll a cylinder with a brake by bending a flat piece a few hundered times in very small increments. Same thing with a cone, just have to "twist" the lines.

    Here's how I do it- First either measure the length or figure out the circumference of whichever piece your working with. I like to start with the big side. Divide that number by the number of bends you want. For me, the circumference (length of the cone un-rolled) was something like 317 mm. I wanted to do 45 bends. Divide the two, that means I have to make a mark every 7mm. Use the dividers, and start marking.

    Kinda hard to see the marks, but their there:

    [​IMG]

    On to the other side. I want the same number of marks, but the circumference is smaller, so the distance between the marks is going to be smaller too. Figure it out the same way- length (circ.) divided by the number of marks, gave me like 4.8mm. Doesnt have to be perfect cause we'll tune it up with a hammer later.

    Second side marked:

    [​IMG]
    #23
  4. dorkpunch

    dorkpunch Oops...

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    Time to bend!

    Start it with the unbent metal to the back, line up the marks on each side, and make a TEENY bend. Slide the metal up to the next set of marks, repeat. Do this 45 times...

    [​IMG]

    [​IMG]

    Eventually it will start to look like this:

    [​IMG]

    In the above pic I was way overdoing the bends. Its kinda hard to judge but not to hard to fix- just clamp it in the brake and pull it out by hand. Its not a perfect science and again, I'm going to have to beat on it a bit anyways.

    All 45 bends made and some adjustments by hand:

    [​IMG]

    [​IMG]

    Not real pretty, but it'll get better. I hope.
    #24
  5. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

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    When using a slip roller, you grab the small end with a pair of pliers or vise grips to hold it back while the big end rolls through. It used to take me 2 or cones before you got it set right and then you would do a production run of 20 or 30 at a time. The finished shape was completed on cone shaped mandrels and a plastic mallet. I used to do hundreds of cones a day.....ugh.
    #25
  6. EvilClown

    EvilClown Standing by to standby for a possible disregard Super Moderator

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    Good stuff.


    :lurk
    #26
  7. dorkpunch

    dorkpunch Oops...

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    That would work but my slip roll is a 2" dia? Cant remember. The cones I'm making are smaller than that. It would probably work on the one I just made, but all of the others are teeny tiny. I'll have to give that a try though!
    #27
  8. dorkpunch

    dorkpunch Oops...

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    With the cone sorta rolled, its time to get the hammer out.

    A stake table comes in really handy...

    [​IMG]

    I dont really have a clue what I'm doing, just working it around the stake until it gets smaller, then work on the shape. Round is good, oval is not...

    [​IMG]
    #28
  9. dorkpunch

    dorkpunch Oops...

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    Time for some welding.

    [​IMG]

    Heres what I've learned so far about welding really thin stuff. I was hoping to do it with the 110 wire feed I have set up with gas, but its kind of a cheap welder and I couldnt get the wire to feed slow enough or the heat turned down far enough. Kept makin messes. I ended up using a Miller 110 wire feed with flux core wire. Flux core wire sure makes for ugly welds but they look okay once you clean off the slag and it seems to be penetrating great.

    Heres my tips and tricks for welding thin stuff:

    1. Make sure you get your two pieces of metal as close together as possible. NO GAPS or you'll be blowing holes, which are hard to refill.

    2. Tack it together a LOT. About 1 tack every inch or so.

    3. PRACTICE a bunch first. Welding flat in the center of a sheet is WAY different than welding a butt joint with two pieces of metal.

    4. Fill in between two of your tack welds, flip it over, and fill in another section on the other side. Go back and forth. Keeps the heat down and lowers the possibility of blowing holes in your metal.

    5. If you can, WELD DOWNHILL. The puddle flows down, it will make you move a little faster keeping the heat down and hopefully helping you to not blow holes in your metal.

    6. KEEP THE HEAT DOWN. For me, what this meant was that I would weld for about 1 second, pause for a second, weld for a second, pause for a second, all the way across the section I was welding. ON, off, ON, off, ON, off.

    I'm starting to get a lot better. Still get a couple of holes every now and then, mostly because my cuts and cones arent perfect and I have some gaps to fill. Gaps are hard to fill. :bluduh
    #29
  10. dorkpunch

    dorkpunch Oops...

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    I clamped the two ends together with vise grips and tacked the two sides together. On a couple of the other cones that were being stubborn, I was able to clamp them, tack them just at the ends, and then hammer them in on the stake table to close the gap. With the gap closed, then I finished tacking it together down the middle.

    [​IMG]

    aint pretty, but its done. This was the first one, the rest get a little better.

    [​IMG]

    The largest divergent cone and the belly all welded up. The belly turned out great, but it was about as perfect as you can get- straight lines, no gaps.

    [​IMG]
    #30
  11. dorkpunch

    dorkpunch Oops...

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    Now the real fun begins. Gotta join them two pieces together. again, if at all possible you want NO gaps. I had a few but it worked out okay. Test fit the two peices, if they are way off its pretty easy to grind one down a bit until they do fit nicely.

    I tacked one side, flipped it over, and while applying pressure (bending it together) I tacked the other side. Everywhere it was lined up nice I tacked it, everywhere it was a little off I beat it in as close as I could with the hammer, then finished tacking.

    [​IMG]

    Then like I explained earlier, weld a bit, flip it over, weld a bit more, flip it back...

    [​IMG]

    And sorta finished.

    [​IMG]
    Hopefully, by now you should have figured out that I have absolutely no idea what I'm doing. :lol3
    #31
  12. dorkpunch

    dorkpunch Oops...

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    Carry on.

    I tried the pliers and slip roller method, and it worked okay but it was pretty hard to get down. My slip roll is too big to get it even close, but it did work.

    [​IMG]

    End result:

    [​IMG]

    after beating it up on the stake table.

    [​IMG]

    Tacked together:

    [​IMG]

    Welded and attached to the rest of the pipe:

    [​IMG]

    [​IMG]
    #32
  13. dorkpunch

    dorkpunch Oops...

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    Now for the convergent cone!

    [​IMG]

    and attached:

    [​IMG]

    Starting to look like a pipe.

    Hey look! One of my welds actually looks half decent. :huh

    [​IMG]
    #33
  14. dorkpunch

    dorkpunch Oops...

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    Last pic for today- Finished the first divergent cone and attached it. Put a little twist in it, hopefully I guessed right and saved myself some work when I go to hack up the pipe and fit it to the bike.

    [​IMG]

    I think its starting to look pretty good if I do say so myself. I found a small chunk of pipe from a bicycle frame to use for the stinger, plan on getting it attached tomorrow. Then all I need is the short section from the header with the nut to attach it to the jug, and then the HARD part begins. Ug.
    #34
  15. McJamie

    McJamie STROMINATOR

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    Somewhere in my library ( a 12 foot by 10 foot shelf in the garage, full of motorcycle magazines, etc......), I have an article in a "Cycle" magazine on how to build and tune expansion chambers. I don't remember all of it, but I think it did say that having the fatter part of the chamber closer to the head pipe equals better midrange, so the opposite is moving it down means more top-end. I've never built a set, but I'm quite impressed with your work. Maybe even a little inspired.
    #35
  16. mike-s

    mike-s 2 squeaky wheels

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    Keep up the good work. I love these d.i.y. threads.
    #36
  17. dorkpunch

    dorkpunch Oops...

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    Thanks guys, but it probably looks a lot better than it is. I do believe that its airtight and my welds will hopefully hold up to the vibes though. I'm just hoping this will get the bike to be able to hold 55 mph semi-comfortably. :D
    #37
  18. dorkpunch

    dorkpunch Oops...

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    One last one for a while. At least, until the header pipe shows up. Added the stinger.

    [​IMG]
    #38
  19. markk53

    markk53 jack of all trades... Super Supporter

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    That looks way too small in the center, the stinger too large (MB5 had a handle bar end since the ID was near perfect), and the head pipe too long. I did an MB5 pipe using Gordon Jennings forumulas from the Two Stroke Tuner's Manual (or Guide, I forget which it was). The pipe let the bike rev like 12,000 rpm in spite of the ignition limiter they used to retard the ignition. It had a whole lot larger center than the one above, I'm thinking like abotu 3" or 3-1/2", but that was like twenty years ago, and a lot shorter tail cone (forget the proper terminology - convergent?).

    See if you can find the formulae necessary to figure out proper size OR find a similar size engine and measure up the pipe on it. The cone dimensions are critical to performance. Maybe one of the current scooter chambers might help give information for you. Carb size and other data come into play too.

    Here's an interesting site with some softwarehttp://www.buildandclick.com/
    #39
  20. markk53

    markk53 jack of all trades... Super Supporter

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    This looks a whole lot more familiar. I take it this was not that first attempt and I'm not imagining things.
    #40