Removing Dents From A Pipe : 2 Methods

[oldgeek]

First I should mention that while there are dangers using this method to remove dents from a pipe, I think it can be done safely with care and experience, at your own risk, of course!

Also I don't recall who on this forum told me this could be done, but it was here that I heard about it.

I made 2 block off plates for the pipe. 1 of the plates has a fitting for my nitrogen tank. I made gaskets to seal the plates to the pipe from a section of bicycle inner tube.





It was hard to take decent before and after pictures, and they don't really show the damage or repair very well. The damage was pretty bad across welds and seams and flattened on the smaller section of the pipe in 2 places.











I hooked my nitrogen regulator to the fitting on the plate to check the seals for leaks. The seals were good, however there was a 2" split in a weld that I didn't know was there. I decided to try fixing the dents without fixing the weld, but I learned that was a waste of time, it only opened up the split more. I then decided to try and weld the seam up with my ox/acty torch using the only filler rod I had handy, flux core mig wire. I have never done anything but braze copper with a torch, so this was new to me. It went rather well after I got the heat adjusted right, and got the hang of it. I had several pinholes pop up while blowing the dents out that I had to stop and repair. After getting the pipe pretty well sealed up, I started heating up a dented area cherry red with the torch, then I reached down and cranked my nitrogen regulator to about 150lbs watching closely as I continued heating the dent. I could see the dent pushing out, and it was fairly easy to control the temp. The dent only moved when it was really, really hot, the moment you remove the torch it stops moving. I ended up using just over 200lbs of pressure on the nitrogen regulator to push the dent out of the smallest section of the pipe. I would think you would use MUCH LESS pressure on a larger section of the pipe. Overall I am very pleased with the outcome of the repair. Now I need to make/get another silencer tube because the carbon fiber one that came with it is shot.

[90GTVert]

Here's a look at the dents in a Leo Vince ZX for a Zuma, shown with the un-dented Aerox 100cc ZX.




I decided to go ahead and try to freeze the dents out of the exhaust. Here are a bunch of shots to give you kind of a 360 view of the dents.


















I filled the pipe with water the best I could. Some suggest submerging the pipe to fill it faster. That would be a good idea. I took the more time consuming method for some reason and filled it from a faucet. Once I got a bit of water in there I plugged the stinger end of the pipe so I could move it around without the water coming out, because I had to fill a little then change angles to get the water to go through the header and into the body. Kept doing that till it was full and then capped of the header using an aluminum plate and an exhaust gasket.






I've seen some people saying sealing is not necessary and others saying it is. As you can see, I opted to seal it. I don't think it was necessary for me, at least not on the stinger end. The rubber cork was pushed out during the process, once everything was pretty well frozen. I think if you have dents in the larger, more central, areas like I did, the small areas on each end like the stinger and header will probably freeze up and contain the pressure in the larger areas.

I put the pipe in the freezer at 3PM, wrapped in a towel to keep my TV dinners clean. By around 8PM it had frozen up and pushed the rubber cork out of the stinger end. I checked it about every 30 minutes to an hour until around 11PM and saw very little change before I went to sleep. I woke up at 3:30AM and found that the dents had been mostly removed. I was quite happy to see this and stayed up till 4:30AM, checking each half hour. At 4:30AM I saw no more change and opted to go back to sleep for a bit. I got up at 6AM and the dents seemed the same, but I decided to give it a little more time before giving up, even though I didn't have much hope for the dents coming out anymore since it had been 2 1/2 hours since I noticed them pushed most of the way out. I also set the freezer to it's coldest setting to see if that would do anything. I removed the pipe from the freezer at 9AM when I noticed that it had busted open. It broke open where the Leo Vince Hand Made stamp is. It seems the stamp made this area the weak spot. I don't fault them for that, it seemed to hold up to a bit of pressure before letting go, and I'd prefer it to bust there than at a seam where it may distort worse and be harder to fix.













So the actual dent removal was done within 12 1/2 hours in my case. Possibly a little sooner since I was sleeping and not checking between 11PM and 3:30AM. I don't suggest using my time as a guide though. Volume of the pipe, temperature, material, material thickness, and probably other variables could change the time significantly. I'd suggest freezing the pipe in the morning on a day when you will be able to check on it often. Perhaps settle on the dents being mostly removed rather than busting your pipe open like I did. Look for signs of swelling in areas that aren't dented and remove the pipe from the freezer if you see that. Be prepared for the possibility of the pipe splitting or cracking and needing to be welded if you choose to try this method. Do it at your own risk.

I was very pleased with the results, other than me leaving it in the extra time to cause damage. The dents are much much better. Still present, but barely. Here are a bunch of shots all around the dented area after the pipe was frozen.


















After everything thawing out, I bent the blown out area back and welded it up. I painted the pipe with BBQ black to keep it from rusting and re-installed it.

[niz76]

  This is not a new idea or a new trick by any means, but I wanted to show my experience with getting a dent out of an exhaust.

About a week ago I purchased this Leo Vince ZX exhaust from Ebay. The shipping was a little slow but I was happy to see that it had arrived...




What I saw when I flipped the exhaust over did not make me so happy. There was a huge dent in the bottom! Of course the ebay seller failed to acknowledge this huge dent or even show it in his two pictures. Well crap...




  Now I know these LV ZX exhausts for the Zuma have a slight dent in them to clear the center stand but this was not that dent. This one is really big and I questioned whether or not it might affect the performance. I immediately filled it with water and put it straight into the freezer for the old 'expand the dent out with ice' trick.
  I took it back out of the freezer after about 8-10 hours and there was no change. The dent was still there and the trick didn't work. 



  I didn't give up there however!
I did a little reading online about the process and it seems that a few folks had good results with capping off the ends and also doing more than one freeze application. I was a little nervous that sealing the pipe off could result it in splitting the seams wide open but I gave it a shot anyway...



I sealed one end off with the block-off plate that I had previously made for use when leak testing an engine. That worked great!



For the silencer end I found a rubber cap that just happened to fit into the end nicely and zip-tied a large washer over it...



  Hopefully the zip ties would pop before the whole pipe split open. Well, hopefully it just pops the dent out! Back in the freezer it went for try #2....



Another 8 to 10 hours went by and I pulled it out. The result?? Drumroll Please........................................................................................................................................................................................................................................................................................................................................................

It Worked! Yay! It didn't take the dent out 100% perfectly but I'm very happy with the results! Here's some side-by-side before and after pics: 

     

Not perfect but much better! So as you can see, this old trick really does work. 

Now to go give that Ebay seller a piece of my mind! haha.