There are several ways. You could get someone else to do it for you. I've heard lots of good things about Pacific Crest Pipe Repair company that John pointed out. If, on the other hand, you are a bit of a DIY fan like myself, you could try fixing it on your own
.
The first method is to fashion some sort of plugs for the ends of the pipe. They have to seal properly and stay in there pretty tight. Then partially fill the pipe with water and place it in the freezer. As the water turns to ice it expands and pushes the dents out. The downside of this method is that it can actually tear your pipe in half if you fill it up to much or leave it in the fridge for too long. I've heard some people plugging up only one end so that the excess ice can go out the other end, but i would imagine it might relieve the pressure to much and then nothing will happen.
The other, far more popular method is the old compressor and blowtorch approach. You seal the pipe, heat the dent until it's glowing hot, and then apply pressure (or vice versa). I tried it myself with a propane torch, and i don't think it was hot enough, even though I raised the pressure until one of the seals failed and shot some 20 meters down the street
(good thing no one was walking by
). Then again, i tried it on a thick stainless steal four stroke vintage russian motorcycle header pipe
. It might be hot enough for the thinner modern two stroke pipe. Also you can even use a manual car tire pump if you have one, instead of a compressor, just put a tire valve in one of the plugs... Just be carefull not to actually melt the pipe if you use something like oxy acetylene torch.
And finally, you can drill a hole, put a hook through it, and pull (or hammer) on the hook until the pipe is straight (or weld the hook straight to the pipe and cut it off later). You will have to weld the hole shut again and it will look a tad rough, but it works
.