Make (bend) a header pipe??

[sodhead]

Maybe some of you machinist or engineer guys out there can enlighten me,,

I’ve been tinkering around with a project of putting an XR75 engine in a KX80 chassis. I’ve got the frame and engine mounts worked out pretty descent, and with a little creative intake and exhaust plumbing, I got it going. I’ve ridden it several times, and it seems like this engine/chassis combo works pretty well together.

I used the original XR75 pipe to make the exhaust system. To route the pipe where I needed it to go in the new frame, I cut it into several pieces, then welded the pieces back together in the orientation I needed. This did work, but obviously not a real smooth flowing affair, and it is a bit of an eyesore.

I was thinking, if I had a good way to bend tubing, I could make a nice flowing, contiguous header pipe that goes all the way back to the muffler. Also, I might be able to use tubing slightly bigger than the original XR75 pipe and let it breath a little easier. I’ve been experimenting with one inch electrical conduit, but the benders for that size are pretty limited in the arc of the radius of bend. Obviously, to make a pipe for a bike, it needs to be a fairly tight radius bend to come out of head then make a 180 degree turn to snake to the rear of the bike. The benders I am fiddling with don’t even come close. I also tried spring type benders, but the pipe just ends up kinking. How the heck do they bend tube to those tight radius curves found in bike exhaust headers??

 

[dave186]

Have you tried a mandrel bender like good exhaust shops use? They dont kink the pipe if you have a mandrel for that size of pipe. Talk to a muffler shop, they should be able to help.

 

[Rich Rohrich]

With light gauge tubing I've had pretty good luck filling the tube tight with dry sand capping the ends of the tube and using heat to facilitate making the bends. As Dave suggested mandrel bending is the best solution if you can convince someone local to do it for you. You can also talk to Aircone 702-566-1077. They can make up anything to your spec for a reasonable price, or talk to Burns Stainless 949-631-3184 if you want to go full metal trick.

 

[sodhead]

I did think about an exhaust shop. I'll check to see how small of tube they can work with.

Rich, what exactly is "light gauge tubing" (not electrical conduit, or black gas pipe from a hardware store obviously) and where could I find some?? I would like to experiment around with the sand/heat idea a little.

Thanks for the feedback guys!

 

[jmics19067]

light gauge tubing would be refering to thin wall pipe

Pipe and tubing are classified as being different even though they are the same shape. Most of the differences is that pipe is measured by inside diameter and by bursting strength<strictly related to something flowing inside > while tubing is measured by outside diameter wall thickness and the physical characteristics of the shape, size ,and material for structural construction.
I would have no clue as to what conduit would be considered since it really does neither. For your intentions most exhaust shops buy straight tubing to make exhaust pipes.
If you feel like waiting J.C.Whitney Co sells mandrel bent tubing in different sizes and shapes thru their mail order magazines. ie 180degree bend, 3"radius, 1 3/8" tubing or 90 degree bend, 6 "radius ,1 1/2 tubing. You will have to weld on the straight sections but atleast you wont have a kink in the middle of the bend from bending or cutting at an angle and welding back together

 

[sodhead]

Yeah, I saw that exhaust tubing in whitney too, but as mentioned it only goes down to 1 3/8" ID. The stock pipe was smaller than 1" ID, so I was thinking 1" ID would be nice.

I'll go to a local shop tomorrow and see if they can do it. How small of tube does a typical shop's mandrel bender go anyway?

 

[jmics19067]

unfortunately an automotive exhaust shop probably wont have anything small either.

there is a company called MCMaster Carr that handles all sorts of differrenty materials and tools. There is one in Elmhurts Ill dont know how far away that is from you but...

mailing address is
po box 4355
Chicago, IL 60680-4355

plant location
600 County Line Rd
Elmhurst, Il 60126-2081


Sales Ph # (630) 833-0300
fax (630) 834-9427

They will have the tubing you need but they probably wont have it pre bent.

 

[Luke Davey]

Sand packed tubing!!

What Rich said works very well, I have seen my uncle make several exhausts for old Triumph bikes by packing the exhaust tight with sand and sealing the end . This stops the pipe from collapsing os kinking, also helps to heat the tubing with OXY.

 

[David Trustrum]

If you want to go welding crazy you can cut straight tube on a few degree angle & rotate it 180 to create a bend. Repeat in a lot of steps to make it a smoothish bend. Sections can be done & smoothed out on the inside before welding together.

I’d plug for the muffler shop but doubt they would have tubes that small so try a gas fitter or something.

Also the XR75 will have a somewhat modest output, but that’s cool, however I would stave away from increasing the header diameter, as unless you have done serious work to the engine you are more likely to just loose midrange with little benefit up top. Stock size is likely to be optimum for the small ports.

 

[SFO]

I have a local tube bending shop that has a cnc internal mandrel bender.
If you have a similiar shop locally you can hound them for scraps.
Seamless ss tubing bent at the minimum radii...
And cheap cheap...

 

[sodhead]

Just got off the phone with a buddy of mine who works in a shop that makes livestock gates and fencing. I thought they only worked with square shaped tube, but he says they use round stuff too and that their bender can bend one inch round tubing.
Anyway, I'm going to go there tomorrow evening (his boss said we can use the shop after hours) and were going to experiment a little.

I'll let you know...

 

[MikeT]

I'd ask the exhaust shop how small a tubing they can get. You might be surprised, plus you won't have to worry about the gage because it will already be right.

 

[sodhead]

Yeah, in addition to my experimenting, I plan to call some shops (exhaust and machine) to see what they could do. In addition to my quest for an exhaust for my project, this is also an oppurtunity for me to tinker around and hopefully learn something.

Thanks for the warning on pipe size David. I knew not to go too large on the size, which is why I felt the typical 1 3/8" automotive type exhaust pipe wouldn't work. The stockpipe size for the XR75 measures about .995" OD, so I thought a 1" ID would be perfect (just a little bigger as I plan on some future orders from Powroll). ;)

So that I use the correct terminology when I talk to the guys at the shop(s),, if a bend is say a 4" radius,, does that mean if it were bent into a 360 degree circle, it would measure 8" in diameter (diameter = radiusX2)? And if this is correct, would it be 8" in diameter from the inside edge of the tube to inside edge, or outside edge to outside edge?

 

[jmics19067]

I believe your 4" radius bend would be 8 " from center to center of the pipe

but if you tell them how you measured it it really shouldn't matter. ie outside to outside. also you can take them the pipe you made and just let them use that as a model with the only difference is just being a smooth bend.<what I think I would try first>

 

[sodhead]

Thanks.

The current pipe that I made is routed a little different than what I plan to do with the new one. I've found a little better way to route it.
That does give me an idea though,,, I could get some soft smaller copper tubing and bend it exactly how I need it, then I could take that to a shop and aske them to use it like a template to make a pipe out of steel tubing and in the size I desire.

 

[David Trustrum]

I was going to suggest real stiff wire for a template, but if you can bend the tube ok. Also when bent the tube shrinks a little so you want to tell them the diameter you want after being bent.

 

[sodhead]

Well, this is what we came up with using the bender at the livestock fencing shop my buddy works at. Didn't turn out too bad. That bender is pretty old and the dies are pretty worn, so we had trouble with crushing and kinking of the pipe. The sand trick did help alot. Couldn't get as tight a bend as I would have liked coming out of the head, but it is better than the pipe I made by cutting and welding. We actually had to make this pipe in two pieces (because of limitations with the bender) and weld them together. The seam is the spot that has been ground on about in the center of the picture. I'll probably continue to experiment with the sand and heat method and see if I can get one bent on a little tighter yet.
And yeah I know guys, the plastic, tires, etc. are junk on the bike. As soon as I get the mechanical details all worked out, I'll make er pretty.

 

[jmics19067]

wow that looks great if you ask me. If you are still in experiment mode I would suggest taking the fork springs out and run the front suspension and steering thru all of its possiblities. I have a kx80 frame here also that i am looking for an xr engine for. heh if I ever do get it together I am sure to look you up for some insight!

 

[David Trustrum]

Seems to fit the bill.
You might want to make a heat shield near the seat or it may burn through the side-cover or the rider’s thigh.

 

[Pantaz]

The tubing is best bent using a mandrel bender. This uses an insert placed inside the tubing, which is pulled through during the bending, thus eliminating any reduction of the inside diameter.
Look in your yellow pages under "Tube Bending" and/or "Fabricating".
If you don't have any luck, send me a private message and I'll be happy to help you out.

-- Mike

 

[sodhead]

I called around town today to see what the local shops could do. The exhaust shops say the smallest pipes they work with are 1 3/8 (too big).
The machine shops say they can bend the smaller tube sizes, but they all say they cannot bend a radius as tight as I am wanting.

An older gentleman that I work with told me he used to make dies out of hardwood by turning them on a lathe. He would then pack the tube full of sand and bend it around the die. Considering the results I was able to achieve using the LOOSE fitting dies on that old bender at my buddies shop, I'm thinking if I made a die with a nice tight fit, I may just get what I'm looking for.

Its pretty interesting to hear how people used to do things before the hi-tech tools and machinery we have today were invented. And I find it equally interesting trying those techniques and methods and finding that they actually work!!

I have been reading about mandrel benders. They definitely look like the tool to use to make those perfect bends. But, a little distortion in the bend would be acceptable to me if I could get the radius and shape I want. If in the end I find I just can't do it myself, I guess I'll go on a hunt to find someone with a mandrel bender.

I know, I know.. I'm stubborn. But the fact is, I'm having fun experimenting around with this, and I am learning alot trying.

I’ll keep you posted on my progress.. hopefully it will be “progress”! ;)
Well, I guess my next step is to find a big ol hunk of some type of hardwood…

 

[demographic]

I worked in a fabricating shop a few years ago and we bent thinish pipes into park benches using the dry sand with plugged ends and oxy torch method with pretty good results. I just have to say that this thread is one of the more informative ones that I have read for a while