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Old 01-28-2011, 06:16 PM   #1
dorkpunch OP
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"Homebuilt" expansion chamber

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:





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!
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Old 01-28-2011, 06:20 PM   #2
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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!!!

Quote:
Originally Posted by dorkpunch View Post
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:





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!
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Old 01-28-2011, 06:22 PM   #3
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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!



Metal with the patterns traced on:



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!

Cut the straights with my squaring shear:



Cut the curves with this handy gadget:



and Viola! The begginings of an expansion chamber.



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Old 01-28-2011, 06:25 PM   #4
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Quote:
Originally Posted by Valleyrider View Post
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!!!

That spring was what was holding the thing up when we found it in the grain bin. It didnt even have a rear wheel. 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.
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Old 01-28-2011, 06:33 PM   #5
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If you haven't already seen it, this will help for all things involving ring-dings- The two-stroke tuner's handbook


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Old 01-28-2011, 06:55 PM   #6
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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
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Old 01-28-2011, 08:29 PM   #7
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Cool stuff dorkpunch, new pipe looks way better already.
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Old 01-28-2011, 09:11 PM   #8
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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.
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Old 01-28-2011, 10:16 PM   #9
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My friend JP Morgen from San Francisco makes many things, among them pipes for his own bikes.


All TIG welded.




Here are the Paper templates for that very Pipe.


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.


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


Enjoy
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Old 01-28-2011, 10:22 PM   #10
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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!
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Old 01-28-2011, 10:36 PM   #11
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Oh for the love of two wheels!!! 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???
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Old 01-28-2011, 10:42 PM   #12
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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.





Viola- one center section ready for welding!

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Old 01-28-2011, 11:03 PM   #13
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Quote:
Originally Posted by Ricardo Kuhn View Post



Here are the Paper templates for that very Pipe.



Enjoy
Great post, as always, Ricardo. Thanks.
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Old 01-28-2011, 11:21 PM   #14
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Quote:
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I recon with that pipe yoo will have a 50 rev power band at 13,500
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Old 01-29-2011, 08:07 AM   #15
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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
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