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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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    Dont know if this belongs here in old school, but since its for my '67 YL2, I figured this was as good a place as any.

    Little background. P.O.J. was my first ever motorcycle. Found it in a grain bin about 15 years ago. Finally got around to getting it road worthy for the first time ever last summer. Been puttering with it ever since. I needed something to do (yeah, right) and wanted to work on my welding / sheet metals skills and figured this would be a good project. My first attempt came out so-so. I used a free internet program to come up with the sizes for everything after I "blueprinted" my engine. Turned out like this:

    [​IMG]

    [​IMG]

    While it worked okay and I learned a ton about cones, oxy/acet welding, and expansion chambers, it wasnt all that great. I had a TON of power at a VERY high rpm, but it couldnt get to that high rpm in the top gear. So, here we are at the second attempt!
    #1
  2. Valleyrider

    Valleyrider I Survived The '60s

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    Not bad at all for your first attempt!!! Needs a more volume in the mid-section (about the diameter of the air cleaner) and a little shorter stinger. Maybe shorten the stinger by 1/2.
    I also like the centerstand spring!!!

    #2
  3. dorkpunch

    dorkpunch Oops...

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    I bought an expansion chamber design program, and it produced numbers more in line with what I though I should have from what I've been reading. Two stroke Tuning by Alexander Graham Bell- Excellent book.

    The program takes your info and spits out a sheet with lengths and diameters. It comes with a second program that will print to-scale cone layouts for you to cut and trace. Works great!

    [​IMG]

    Metal with the patterns traced on:

    [​IMG]

    Next step is to get busy with cuttin machines. I'm lucky- I teach metal shop at a junior high. A lot of these photos are going to be used when I write directions for tools, PLUS I get better at my job while practicing with the tools!:deal

    Cut the straights with my squaring shear:

    [​IMG]

    Cut the curves with this handy gadget:

    [​IMG]

    and Viola! The begginings of an expansion chamber.

    [​IMG]

    [​IMG]
    #3
  4. dorkpunch

    dorkpunch Oops...

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    That spring was what was holding the thing up when we found it in the grain bin. It didnt even have a rear wheel. :lol3 I've got a couple of other threads on this bike going- trying my hand at "writing", going through the history I remember of it. Also got one dedicated to the build last summer, but its nuthin like your Yam, thats a beaut!

    I think the new program I'm using will give me a lot better results. It says the stinger should be almost the same, but both the divergent and convergent cones are way bigger, and the belly is quite a bit longer too.
    #4
  5. Tosh Togo

    Tosh Togo Long timer

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    #5
  6. Abdelhub

    Abdelhub Blanco Trasho

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    That looks great. What is the name of the program? I like how you can just trace then cut.

    I got a few old two strokes that could use some exhaust work.

    only tough thing i see is maybe getting the cones rolled well (at least for me)

    Great work.

    Mike
    #6
  7. anonny

    anonny What could go wrong?

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    Cool stuff dorkpunch, new pipe looks way better already. :clap
    #7
  8. dorkpunch

    dorkpunch Oops...

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    The software is called 2 stroke wizard, bought it here: http://www.buildandclick.com/ it came with a 4 stroke header design program as well for $20.00. Was kind of a pain to install though. The cone layout software seems like you had to download seperately but it was free. I struggled with rolling the cones too, until I talked to a local sheet metal guy. Gave me a great idea called microbraking- you "roll" it using your brake. Pics to follow. :deal
    #8
  9. Ricardo Kuhn

    Ricardo Kuhn a.k.a. Mr Rico Suave

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    My friend JP Morgen from San Francisco makes many things, among them pipes for his own bikes.
    [​IMG]

    All TIG welded.
    [​IMG]

    [​IMG]

    Here are the Paper templates for that very Pipe.
    [​IMG]

    But after years of making them using such a laborious method he decide to investigate new methods and came up with a "Water forming" method to produce parts like this from just two parts.
    [​IMG]

    This are just scraps of pipes that did not come out "Just right" but he has build a few complete pipes already.
    [​IMG]

    Enjoy
    #9
  10. dorkpunch

    dorkpunch Oops...

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    I've looked at the hydroforming a lot, I would LOVE to try it but I just dont have the tools available to me. Not that it takes much- basically alls you need is a pressure washer... I've got a shop full of bench tools and no pressure washer, so this is how I have to do it. Good enough for now. Some day I plan on trying the hydroforming for sure though. Cool beans!
    #10
  11. FatBoyCrash

    FatBoyCrash Buckle up SpankY!!

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    Oh for the love of two wheels!!!:D:D MORE!! Don't stop now!! Especially with the 'how to roll up cones from sheet metal'.... !!!!! Does that software allow for bends in the pipe or just give best cone shape/size???
    #11
  12. dorkpunch

    dorkpunch Oops...

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    all right... one more quick post.

    I like to start with the simple stuff. On this pipe, that means the belly. Its just a rectangular piece of metal thats getting rolled into a cylinder. Easy peasy- throw it in the slip roll and crank it through a couple of times.

    [​IMG]

    [​IMG]

    Viola- one center section ready for welding!

    [​IMG]
    #12
  13. fishkens

    fishkens Long timer

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    Great post, as always, Ricardo. Thanks.
    #13
  14. Old fart

    Old fart Keen AG100 rider

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    I recon with that pipe yoo will have a 50 rev power band at 13,500 :evil
    #14
  15. Abdelhub

    Abdelhub Blanco Trasho

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    If im not mistaken in A. Graham Bell's book a pipe with shallow tapers will create a much wider gentler powerband. Usually for motocross, scrambles.

    The really steep cone tapers create a sharp impulse and a very narrow but strong powerband. (road racing)

    Lots of calculations needed, exhaust duration, exhaust port diameter desired rpm for peak power etc.

    Great posts. any more pics you can post are greatly appreciated. I have a villiers engined greeves with the original pre expansion champer exhaust and id love to make one for it.

    Mike
    #15
  16. racer

    racer Long timer

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    I rode the piss out of one those Yamaha 80 backin the 60's. Look around the swap meets and Ebay for a GYT kit. They were sold by Yamaha to hop up the engines. Usually had a, new cylinder, piston, carb and a new expansion chamber. I agree, the chamber is much too small. I've made a few for hill climbers and the converging and diverging cone angles must be steeper with a shorter stinger. Good luck
    #16
  17. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

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    I made expansion chambers for a living back in the early 70's. Here are a few of the very basics regarding pipe design:

    Longer and larger head pipe (the 1st section) gives more low end.

    Longer center section (non-tapered section, typically the second or third section) gives more low end.

    Longer smaller diameter stinger gives more top end.

    Use these basic facts to tweek your pipe to move your power band around.

    The combination of all of the parameters will determine how much power you make or how wide of a power band you get. Beware that you can increase or decrease a particular section to move the power, but at the same time you can reduce the total power made. Guys like Donny Emler (FMF founder) spend hours upon hours with hundreds of different configurations on the dyno in order to get a pipe that works well.
    #17
  18. dorkpunch

    dorkpunch Oops...

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    Now that is some great info right there. I think that about sums up everything I've found on pipe building so far in just a few words! Thanks!
    #18
  19. dorkpunch

    dorkpunch Oops...

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    Maybe I should have backed up a little further... You do need to know quite a bit of information in order to get anything useful out of the program. I'm no math whiz, but I think I could *probably* have done the calcs using Bell's book.... I went the easy way, bought a program, got the numbers, plugged 'em in and hit go.



    Here's how I got all the info I needed (taken from my other post here- http://www.advrider.com/forums/showthread.php?t=596268):

    What I needed was measurements between all the ports and the port sizes.

    [​IMG]

    Get some aluminum foil and roll it into a tube that just barely fits into the cylinder-

    [​IMG]

    Get a balloon (or in my case, a laytex glove) and some compressed air, stick the glove in the tin foil tube, and inflate-

    [​IMG]


    Kinda hard to see, but you can see the dent the glove made in the foil where the port is.

    [​IMG]


    Remove the now imprinted tin foil, and measure away!

    [​IMG]

    Final product, a doodle with numbers:

    [​IMG]
    #19
  20. dorkpunch

    dorkpunch Oops...

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    Man, I love sketchup.... Digitized my port measurements, heres what I came up with:

    [​IMG]

    Rainy day, so I played a bit more. Had the top end off to hone and re-ring, figured that was a good time to degree my engine. Here's what I came up with:

    printed a degree wheel of the internet, cut it out, and bolted it on to the crankshaft. Used a cheapo laser pointer set on the engine to light the degree, set the wheel to zero with the piston at top dead center. Kinda hard to see, but if you look close you can see the red dot at the 0.

    [​IMG]


    [​IMG]

    Rotated it through, noting the degrees that ports opened and also the duration. Had to take the cylinder and piston back off to see the intake to get the degrees for the rotary valve.


    Heres my digitized version. Not sure if its right, seems a little wonky compared to some that I've seen:

    [​IMG]
    #20