A two stroke exhaust pipe

[2T Institute]

I like designing and fabricating two stroke exhaust pipes. I think the average amount of welding in a pipe is 4-5metres. Usualy weld on 19Amps 1mm electrode.
Before anyone says "that's fantastic":rolleyesI'm not looking for fanboi approval as there are plenty better than me at this caper.
I wil in the future be looking to fabricate a Ti pipe and would love some input on purging these types of shapes, if anyone has experience with Ti welding

[PatrickW]

How do you go about figuring out the shape and size of the expansion pipe? Also, where do you source your Ti sheet?

[jrscgsr]

Welding titanium you'll need a trailing purge and a gas lense for your tig torch with the biggest size cup you can get and the pipe internally purged as well. Weld it on as low a heat as possible to avoid an excessive HAZ. Fit up of the joint to be welded will be critical as well. If you've never done it before I would suggest you practice on some scrap first.

[2T Institute]

I snap any suitable scrap off evilpay, and the design is arrived at by a study of the cylinder and intended useage factors.Then you crunch numbers with a simulator.

I have been told to run a purge line to the trailing shield also??? The internal purging gets more difficult as the pipe starts to take shape, as it's not possible to fill the voids.
Yes practice makes perfect.
Thanks for the assistance.

[On fire most of the time]

First, I claim no Ti welding experience...but I will parrot something I heard here from someone that I am fairly confident, knew what they were talking about.

Use cardboard (or something else, simple and easy) as your "cap" and leave a small hole in the end without the purge tube. That would allow flow, and would not result in trapped air that could contaminate the backside of the weld.

Good luck on your project, and post some pictures of it!

[DDM powersports]

I have never built a Ti system from scratch. I have repaired a couple of 4 stroke systems. We did some checking around and the best set up I come up with was to put it in a small sandblasting cabinet. Then purge the whole thing & have a piece of scrap inside. Then start on the scrap when everything is good move over to work piece. Good luck!

[2T Institute]

I'll get some pics together. I would need a big cabinet, an ebay seller has 'bladders' for filling voids for back purging. A wee bit expensive so I'll have to find an el cheapo way of doing it.

[Jigantor]

When you purge the container make sure you have allowed ten times what is required by volume so there is no air left. Remember that argon is heaver than air.
When doing your practise welds if you are getting a silver or slightly straw colour keep going, if blue stop as you still have air.
Also only weld an inch in length, let cool and weld another inch in length, this will help if you have a size 12 cup.

Nice work on the steel pipes.
I have noticed that road bikes have started passing the pipes underneath the frame like back in the seventies so they lower the centre of gravity. Old idea but still works.

Ji

[spotsineyes]

Ten times, really? So if your cabinet is eight cubic feet, you are going to use eighty cubic feet of argon before you even strike an arc?
The last project that I purged with argon was a surge tank for fuel, about five gallons. My super-scientific way of knowing that all of the air was displaced was this: I situated the tank so there was a fitting at the bottom, and that is where I introduced the argon. I taped a couple of other fittings shut, and had one open at the very top of the tank. I screwed in a hose barb with a length of 1/4" rubber hose, which I held by my ear. When the tone of the hissing changed, I knew I was good to go. Seriously!


On dirt bikes, the reason the pipes are above the engine is obvious, to keep from getting smashed. The reason that road bikes started running their expansion chambers above the engines was to lower the center of gravity. If the pipes which weigh nothing are above the engine, then the frame can be designed to lower the engine. Moving the engine has a big influence on c of g, moving the pipes would make almost no difference.
This trend started many years ago, and years after the bike pictured in the first post was in production.
Well, maybe not too long after that bike was made.

[Jigantor]

Hi Spotsineyes,
So was your last purge job welding titanium ?

Ji

[spotsineyes]

No, it was stainless, and the gas was inside the tank, not inside a welding chamber. I was just trying to offer an alternative method to determine when all of the air is displaced. It seems so wasteful to use ten times the volume of your welding chamber. Try it, it surprising that air coming out of a pipe, and argon coming out of a pipe, make a different sound.

My only experience welding titanium was when I fixed a cracked muffler cap from a Yamaha Y450F. I removed the cap and cut a strip of it off from the part that goes inside the muffler body. I then had a piece of welding rod that was the same material that I welded. I then put the cap into a cast iron frying pan, and ran my argon from my TIG torch into the pan for what I guessed to be a long enough period. I then repaired the crack in the open pan, and everything was going well. Then right at the end of the weld, I bumped the pan and it fell on the floor. That part of the weld turned into white powder. The rest of the weld was a straw color.

The point is, it is my opinion that you don't have to be surgically sterile or be scientifically oxygen-free to weld titanium.

[spotsineyes]

Unless maybe for rocket ships or nuclear power plants.

[Jigantor]

Hi Spotsineyes,
Yes I totally agree.
Those chamber manufacturers are the ones that suggest ten times per vol.
I actually wonder if you repair a Ti dirt bike header weather or not you need to purge the pipe at all.
Dirt bike pipes don't last long enough anyway.

Ji

[spotsineyes]

Hi Spotsineyes,
Yes I totally agree.
Those chamber manufacturers are the ones that suggest ten times per vol.

Wow.

I actually wonder if you repair a Ti dirt bike header weather or not you need to purge the pipe at all.
Dirt bike pipes don't last long enough anyway.

Ji

I would guess yes. As bad as stainless "sugars" on the back when you don't purge, I imagine that Ti might not even flow without purging. Of course, I don't know, though.

[Jigantor]

I have been waiting for a Ti header pipe to come in so I can test this.
I have Ti filler rods, Ti grade 5 plate and a size 12 cup ready for the job.

Most exhaust shops here tell blokes that it can not be fixed, then talk them into making them a new header out of SS.

Ji