Exhaust Fabrication: Expansion Chamber

rek4385

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Nov 5, 2010
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Obviously I posted in the wrong section. Could a moderator move this to the appropriate section or remove it. Dont want to be any trouble.


Greetings,

Long time reader here, long time tinkerer shady tree mechanic.and with this being my 2 post on the site I hope this is the appropriate section. Im am going to try and not ramble :)

Application: 49cc zoom engine
Part to add: KX65 expansion chamber - 39mm header pipe size.

To make this a quick and an easy to read question. What is the best way to go about mating my exhaust port to this larger 39 mm pipe on the expansion chamber? FYI Ive googled and searched this site extensively. I find alot of pictures of some awesome fabrications but what are you guys using? Are there exhaust adapters? Where can i get these supplies of piping etc.? My current brainstorm is keeping my current flange, cutting my stock pipe and taking advantage of its curve for clearance issues.the pipe before the mufflers is approx 25mm . after I cut i will weld an adaptor on it but I cant find a 25mm to 39mm adapter size.

I think this question is descriptive enough. I am hands on and technical but lack exhaust technicality experience!
 

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ken murphy

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Sep 19, 2008
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turn your stock pipe upside down n cut it to match the first bend after the stock mount,I make my own gaskets as not to leak,these are leaky lil girls-lil china girls.
If you get that pipe dialed in you'll need a carburator mikuni works good but u will have to fabricate the flange i use a washer and copper pipe n alot of fab'n.wee..wee..shft.dnut:-||
 

rek4385

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Nov 5, 2010
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Pretty pumped to see all of your responses. I should of labeled the title of the thread " All Fab'ers rise".....loving it. The kiddies are sick which prevented a timely response. Thanks again.

MILD STEEL 1-1/2 in. DONUT - C76-560 at The Chassis Shop I know that these guy's make donuts in different sizes. You then cut the donut out where ever and re-clock it to your desired need. Don't know if that will help.
Wow,I want to ask "Where the hek did you find that?" Ive never seen anything like that.That helps to know something like that exists and not these gas bicycle engines. The donut is just begging to be turned into a potential piece of exhaust "art".

turn your stock pipe upside down n cut it to match the first bend after the stock mount,I make my own gaskets as not to leak,these are leaky lil girls-lil china girls.
If you get that pipe dialed in you'll need a carburetor mikuni works good but u will have to fabricate the flange i use a washer and copper pipe n alot of fab'n.|
Leaky little things ,my words exactly. Loud and dirty too.The EPA is loving it.In passing I have heard of mikuni carbs. Where can you get them cheap?I assume that the new volume/flow of the chamber will induce a lean mixture, a lot learner then what my stock nt carb can compensate for? Fab'n wee wee these little 2 stroke dirties are cheap, its the addiction of modfabn' which in turn requires more tools that gets expensive LOL.

Repeating it back to you:Ok so harvest the stock 2 bolt flange. Cut and fabricate the down pipe to match the angle of the chamber inlet pipe. I can take advantage of using copper pipe and fab'n large washers as flanges (I like that idea).

Rek4385 Where did you find that pipe? Just curious its growing on me a little.:D It looks like a pipe for one of these.

Thinking about shoving it onto one of these perhaps even after a little moding http://www.herdan.com/images/042374.JPG
That engine looks like a gem. slapping a chamber on there , oh our hearts delight.

I bought it from a guy on Ebay he says it came off of a kx65. The picture shown is not the exact brand. That picture was found via googling "kx65 expansion chamber" and then photo's. Ebay prevents me from saving the picture of the item found on the ended auction page and it is currently in the mail) Things will get interesting when a actually have it in my hands to evaluate. It appear large with a lot of volume. I am assuming the final outlet pipe will need to be small, this is the least amount to worry about , and that dialing it in will be a chore.

heres one of my up pipes
repost...your picture did not go through!
 

rek4385

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Nov 5, 2010
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http://motorbicycling.com/f51/expansion-chamber-resonance-25085.html
You might find this thread of interest it just sprung off too.

A member Camlifter gave us that swell link to the donuts. I thought you would like that..
Thanks for passing on that thread. A wealth of knowledge and information indeed. Including all the links you guys pass on, bookmarking them all!

I recieved my expansion chamber today and I am pumped...what a beauty it is. I am always pumped that the bend in it will work perfectly with my application. the only fabbin I will need to do will be to match in to a flange. I will some home need to fabricate a flange and make it fit. Not sure in how I will be able to do that for obviously the exhaust port is about 25mm and the chamber pipe alot larger.

So I am left looking around online for a supplier of flanges, hoping to stop by home depot saturday morning and see what I come up with there with piping and other supplies. Hopeing that I can do some brazing because I do not have access to a welder and brazing is cheaper. we will see. Ill try and post some pictures soon of the chamber to show you all what I am working with. Thanks again guys.....
 

culvercityclassic

Well-Known Member
Sep 27, 2009
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Culver City, Ca
I am not sure what happened to REK but we have so many options on this site for expansion chambers. Just look for a dealer and they can help....hint SBP...I ended up making my own but thats me.

Good luck... CCC
 

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,508
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Rek4385 Where did you find that pipe? Just curious its growing on me a little.:D It looks like a pipe for one of these.

Thinking about shoving it onto one of these perhaps even after a little moding http://www.herdan.com/images/042374.JPG
Hey Goat Herder, those Pro Circuit pipes work extremely well on Morinis!

And rek4385, it's pretty simple to fab an exhaust flange or just adapt the stock pipe flange to the PC pipe.
 

Dogtown Burner

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Sep 15, 2011
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MILD STEEL 1-1/2 in. DONUT - C76-560 at The Chassis Shop I know that these guy's make donuts in different sizes. You then cut the donut out where ever and re-clock it to your desired need. Don't know if that will help.
oh such a great idea! too bad they (and no one else apparently) make 1" donuts. 1.5 is pretty darn large for a 66cc exhaust. hmmm.. I too have a kx-60 expansion chamber, a bike, an engine, and a dream...

bummer thing is, after a lifetime of riding 2stroke racebikes, I only recently learned that the rocketship powerband those bikes have is due to the power valve in the crankcase, combined with the reed valve intake., and a team of japanese engineers spending years perfecting the combination of systems to achieve this result. I guess the china girl expansion chambers simply make a slight improvement in power, but no drastic change. still a bargain of fun for $150. No way around it, they're still fun.