DIY (sort of) hydraulic pipe expander

[djb25]

I have another thread where I'm starting to detail the process of turbocharging my 2.7l 911, but this post is about the hydraulic pipe expander I "made" or "hacked together" today.

Anyway, part of the plan for the car is to build my own (simple) exhaust system. I've ordered some mandrel best stainless tubing and stainless mig wire. I'm not looking to make anything amazing, just something functional. While planning the exhaust, I realized that being able to slip-fit the pipe before welding would be very helpful and make the process much easier.

I started looking into these things:



Unfortunately, every pipe expander I found had horrible reviews. It turns out that all the non-hydraulic expanders are really only good for pushing dents out of pipe. There is a Lisle version that has decent reviews, but even that seemed like it would be a stretch to use on stainless pipe (ha!). It seems that to really do it right, you need a hydraulic expander. Unfortunately, they're expensive. It would be significantly cheaper to buy a complete exahust than to buy a hydraulic expander.

Then I started thinking about a DIY hydraulic expander. It seemed simple to do, only you would need a hydraulic cylinder that pulls in rather than pushes out. I had no idea where to find something like that, so I did a web search. And yep, it's been done before.

So all the credit goes to this guy on the Honda forum: https://honda-tech.com/forums/welding-fabrication-53/diy-exhaust-tubing-expander-3020990/

Basically, you get a Harbor Freight hydraulic punch driver kit:



And an exhaust pipe expander like shown above (the Honda guy bought the nice Lisle kit, but I'm going to try the Harbor Freight $19.99 version).

Putting it together is pretty simple. The hydraulic cylinder is hollow. It is actually threaded inside, 3/4"x18 (I think - whatever the standard 3/4" fine thread is). Unfortunately, the pipe expander rod is 12mm, so they don't mate up and a 3/4" threaded rod is too large for the expander. Initially I was going to turn down a 6" 3/4" bolt, thread the turned down end, and spin a nut onto it. But after looking at things for a bit, I decided to just use the rod that came with the expander.

This thing:



I chucked it up in the lathe and turned down the long hex end so that it would fit all the way through the cylinder.



I took the cap off the bottom of the cylinder and used the nut that came with the expander:



A little note about the bottom cap. It is there to hold in a fairly strong spring. That's how the cylinder retracts when you release the pressure. So when you remove the circlip holding the cap on, it will explode. Fortunately, I had it facing away from me and no one was mangled or killed, but the circlip is gone. The cap and the spring hit the ceiling and came straight down, but the circlip may still be in the air somewhere. Just an FYI in case someone wants to try this.

Anyway, here's the final product:



Exhaust pipe should be here tomorrow, so I'll update this with my success or failure.

Incidentally, you don't really need a lathe to do this. A 7" 9/16 bolt or a 7" piece of all thread would probably work just as well, and be faster and easier. Unfortunately, I didn't have anything long enough. Honestly, something 1/2" would probably work as well.

[16Volt]

Interested to see the results.

[Dmitry at Pelican Parts]

+1 thanks for sharing! If you have any other DIYs that you're planning on doing, please take a look at the link below. If we publish your work, we'll give you credit and 10% off your next order. Please let me know if you have any questions!

DIY Project Expert Submission

[Tippy]

Curious how you like it.

[RarlyL8]

Hate to bust your bubble but the first time you use that to expand a standard thick exhaust pipe the metal slats held together by those O-rings will break. Those cheap Asian manual pipe expanders are made of the most brittle metal I've ever seen.

There is a guy on the internet that sells a similar gizmo that is more robust. It's a few hundred bucks but the videos look like it would work well for the garage DIY guy.

[djb25]

Originally Posted by RarlyL8

Hate to bust your bubble but the first time you use that to expand a standard thick exhaust pipe the metal slats held together by those O-rings will break. Those cheap Asian manual pipe expanders are made of the most brittle metal I've ever seen.

There is a guy on the internet that sells a similar gizmo that is more robust. It's a few hundred bucks but the videos look like it would work well for the garage DIY guy.

Well, the expander was only $20 from Harbor Freight. If it breaks, I'll just get the Lisle expander. It's a bit more expensive, but it works the same way.

[RarlyL8]

Great idea, I was just throwing in my $0.02 to save you some curse words later on (guess how I found out). If you can find a more robust expander you're golden.

[djb25]

Well, I got a chance to try out the DIY expander tonight on a piece of 2.5" stainless exhaust pipe.

Drum roll...

It sort of worked. It expanded the pipe a bit, then the bolt stripped the threads out of the nut. Popped right off the end. So... failure number one.

The holes in the expander are 9/16". I didn't have any 9/16" bolts long enough, and I didn't have any 9/16" all-thread, so I used whatever was laying around. Turned out I had a piece of (I think) 7/16" all thread (it might be 1/2" or possibly even metric, I'm not sure). That worked even better, noticeable expansion in the pipe. Then... BOOM! Stuff shot all over the garage. After the smoke cleared, I found this:



It actually pulled the all-thread apart. I had double-nutted each end to avoid the threads pulling out... but apparently it was too much pressure for the lowly piece of all-thread. I have no clue what grade I was using there, but I'm guessing it wasn't anything great. Minimum tensile strength of a 1/2" Grade 2 bolt is 10,500 lbs. 7/16" is 7,850 lbs. So even if it was grade 2, that's some pretty serious force.

It's late, so tomorrow I'm going to bore out the ends of the expander to fit a piece of 5/8" all-thread. That's 16,700 lbs for grade 2, or 27,100 lbs for grade 5. Probably the best option would be to get a piece of hardened 9/16" threaded rod. Or, even better, use the Lisle manual pipe stretcher kit.

On the positive side, it can be made to work. The other problem is that the expander is about 4.5" long, much longer than necessary. Unfortunately, if you put the expander in partially, it will make a cone. So you have to stretch a 4.5" section of pipe, or else put a scrap piece to make up the difference. That's a lot of pipe to stretch. If you could stretch a 2" section only, it should take quite a bit less force. Again, the Lisle is a better design and better suited to this.

Unfortunately, I only need to stretch one piece of pipe to finish my exhaust, and it really isn't worth it to me to spend $200 on the Lisle tool.

[Tippy]

Thanks for the data

[djb25]

Another update on this -

I went ahead and bought the Lisle "pipe stretcher" kit. This is what it looks like:



Item 17350. It was $170 on Amazon.

I received it today, and I have to say, it is a very, very nicely made tool.

It actually has a tapered roller bearing on the driven side of the bolt, which makes me think it probably would work very well as-is, using an impact gun.

The really crazy thing is that the Lisle tool and the Harbor Freight tool both use the same thread and thread-pitch - 3/4" fine thread. They're practically made for each other.

I should get a chance to try it out tonight. I may make a replacement for the disc with the taper bearing - no sense in risking damage to the bearing.

I should note that this is the Lisle "Pipe Stretcher". Lisle also makes "exhaust pipe expanders," which I believe are more for removing dents from muffler claps and such, like the rest of the cheap expanders.

[boosted79]

Neat idea but why not just take the piece you need expanded to an exhaust shop? $10 and you're good to go.

[djb25]

Originally Posted by boosted79

Neat idea but why not just take the piece you need expanded to an exhaust shop? $10 and you're good to go.

Ha. I live in the middle of nowhere. Closest exhaust shop is about 45 minutes away. The local ones closed down years ago.

[djb25]

Okay. It works!

Turns out that stainless steel pipe is pretty difficult to expand (who knew?). I tried to just expand the pipe cold, but it would only go so far. So I pulled out the torches and heated the pipe cherry red, popped it on the stretcher, and pumped away. Worked great. In fact, I overdid it and ended up with a pipe slightly over-stretched. But it will still work.

[djb25]

In case anyone is interested, this is the only additional part needed - a piece of 3/4"-16 all-thread approximately 6" long.



I didn't have any all-thread that size, so I took a 6" long grade 8 bolt, cut off the head, and threaded the other end. Everything bolts right together.

And here's what I have been working on, turbocharging my 2.7l:

[boosted79]

Neat