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"Homebuilt" expansion chamber

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

  1. dorkpunch

    dorkpunch Oops...

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    Yup, the pipe on the bike in those pics was the first attempt. The pipe I'm building is the 2.5 attempt, and its freaking HUGE compared to that first pipe. Had 2 MB5's for a while, fun bikes!

    The first attempt was designed with some web flash applet thingy. This second one I did buy the build and click 2 stroke software. Seems to work great, really like the cone layout printer thingy that comes with it!
    #41
  2. oregoncoast

    oregoncoast Smells like Bacon

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    Great thread...and I don't even own a 2-stroke anymore.... :wink:
    #42
  3. markk53

    markk53 jack of all trades... Super Supporter

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    We had them back at the bike shop. Used the WFO expansion chambers that only slightly improved things, but were obnoxious loud. I cut one up and made it to the Jennings forumulae. It didn't have much punch down low, but would rev for ever in spite of the ignition.

    One guy had the trick though, he cut the cradle out of a CR80 chassis with the engine still in it, welded it in to the MB frame - can you say 70 mph wheelies?
    #43
  4. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

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    When using the pliers on the slip roller, the pliers need to be up against the rollers. You grab the edge of the sheet metal and you hold the bottom of the pliers against the rollers and feed the sheet metal through the pliers letting it slip through the pliers a little at a time. Grabbing the end of the sheet metal and holding it back is the hard way.

    Uggg! Drop the mig welder and use a gas torch with a 00 tip. Tack the end you plan on starting with with both edges touching. At the finishing end, leave a very small gap which will close as you get there. Don't use rod and just fuse the two edges together. You shouldn't need to put any additional tacks in the middle of the seam. The gas welded seam can then be lightly tapped out with a metal finishing hammer. Do not use a metal hammer when shaping the cones, use a wood, leather or plastic mallet for a "dead blow". Most of getting the ends round is done by hand bending the cone into shape around the anvil without the hammer.
    #44
  5. supershaft

    supershaft because I can

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    Did you have one of those smaller than normal mixers and stuff to go with that 00 tip? A friend does and says it makes all the difference in the world. I can weld up pipes pretty slick with TIG but have not figured out how to do it as your are describing with gas and I don't have access to a TIG right now AND need to weld up an exhaust. Last time I used gas I ended up using heat sinks to stop it from warping. Any suggestions?

    No one has mentioned metal grain. I was taught to work with it. I think it does matter when bending sharp bends for brackets and whatnot.
    #45
  6. dorkpunch

    dorkpunch Oops...

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    The first pipe was done with oxy/acet with a 0 tip. Worked, but not pretty. I'll have to pick up a 00 and give it a try. Wire feed has been WAY easier for me- less set up time, less gooping of filler, and less holes. I quite like playing with the oxy / acet though.

    Great info on the pliers trick and the hammers, I'll give that a try on the next go around. Thinkin dual pipes for my John Deere Liquifire. :evil

    I've wondered about grain too... It seems that it bends a lot nicer in certain directions. Anyone have any insight on this?
    #46
  7. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

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    No worries about grain on 16 gauge sheet steel it is just a simple roll that isn't that tight. We would start with 4'x12' sheets of 18 gauge, no concern for grain was ever considered. Once the slip roller was set, you would crank out about 100 cone runs with only minor adjustments (1/8 to 1/4 turn of the adjuster) as you progressed through the run. Once you got it down it would only take a couple of cones to get the set up right and the hammer and anvil we only used to dress the lead edge that didn't bend due to the space to the rear roller.

    The trick to the gas torch on sheet metal is to get in, get it hot in a hurry and get moving. That's why simple fusion without using filler rod works so well, you move pretty fast, prolly at least twice as fast as with using filler rod.

    The small Victor torch was the most common used.
    #47
  8. supershaft

    supershaft because I can

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    Thanks. I have made quite a few systems with 20 gauge and that seems plenty heavy enough to me. Is that part of my problem with gas? BTW, your advise makes sense. I will try faster.
    #48
  9. RecycledRS

    RecycledRS Along for the ride

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    I would add that it helps to use a very low tip angle to the work (and the 00 tip). It seems to help help pre heat the metal ahead and reduce the heat directed at the puddle area giving you a bit more leeway.
    #49
  10. dorkpunch

    dorkpunch Oops...

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    This is why I love the internet... I have no idea what I'm doing but I'm learning a lot!

    Header showed up. Man this new pipe is HUGE compared to the first one...

    [​IMG]

    Gotta figure out how to stuff that pipe under this teeny little bike.

    [​IMG]

    Thinking I'm going to run it out to the left, curve it back under the motor (most of this header is getting wacked off)

    [​IMG]

    And then running it along the bottom of the swingarm on the other side. Gonna try and build some rearsets for it to while I'm at it.

    [​IMG]


    Should I be worried about riding the bike without the skid plate / engine frame support? A lot of the "street" versions I dont think had anything there.
    #50
  11. RecycledRS

    RecycledRS Along for the ride

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    The general rule of thumb is that when you get the pipe right there is no way you can get it to fit the bike (Gordon Jennings). Not an exact quote.
    #51
  12. FatBoyCrash

    FatBoyCrash Buckle up SpankY!!

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    :clap:clap:clap
    #52
  13. anotherguy

    anotherguy Long timer

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    When you calculated length did you include the head pipe you're attaching? If not the pipes going to hit too high and have more overrev than you have RPM.

    From ErlenbachRacing To make turns in sections without reducing the section length. cut the section at half the angle and
    rotate 180deg to make the turn. More cuts at smaller angles make for smoother turns.
    #53
  14. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

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    Oh buddy, you have no idea how much time I have spent trying to get Jennings derived pipes to fit. Many times we built pipes that didn't fit other than to just run on a dyno. Back in the 70's a friend of mine built pipes for Bultacos, which had a frame and fiberglass panels that made making a high pipe all but impossible. His solution was to design a "Snake Pipe" that wrapped around on its self, with the entire pipe in front of the engine. On 70's DKWs we used to make what we called "Fish Pipes" where the cones were flattened to about 1 1/2 to 2 inches thick.

    I have a question regarding your head pipe. Did your design include that length of head pipe? Your pipe look really long, and it looks to me that with your 2 stage front cones, the first cone could actually be considered to be a "Tapered Head Pipe".
    #54
  15. RecycledRS

    RecycledRS Along for the ride

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    I can still remember making a snake pipe for a 400 Maico. I cut and cut and welded and welded. Took a couple of days solid work but it taught me two things. One- never do this again, and two- having the pipe end in front of the rider was very loud. It looked good at the time though.
    #55
  16. supershaft

    supershaft because I can

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    I have noticed that just about all the new chambers have tapered head pipes. Even four strokes have highly tapered pipes now. Stepped up right out of the shoot and tappering this way and that all the way back.
    #56
  17. anotherguy

    anotherguy Long timer

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    Help spread the useful power out. Little short things with big fat bellies. Allows reasonable port sizes/time area numbers and good piston life that accompanies that.
    Not mine-it was for sale last I heard.
    [​IMG]
    #57
  18. markk53

    markk53 jack of all trades... Super Supporter

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    They've been that way for years. With the advent of stamping the bodies, it was even easier. The early Bultacos had the cones start fairly early, short head pipe, made up of rolled cones. The Japanese bikes of the 70s came with stamped steel far more elaborate and internally very smooth cone sets. They were tapering virtually from the cylinder on back. Stamped chambers were like manna from heaven from a cost stand point. A really well built chamber built from rolled cones can be a work of art and have a few dozen welded/brazed joints.
    #58
  19. markk53

    markk53 jack of all trades... Super Supporter

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    Those wrap around pipes were also called "Snail pipes" for obvious reasons.
    #59
  20. markk53

    markk53 jack of all trades... Super Supporter

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    One interesting finding Jennings mentions was the fact that the stinger could actually be inset into the inside of the chamber - an innie! They found little if any difference when the stinger was slid back into the chamber.
    #60