Fixing Dents in Exhaust

The exhaust on the Honda is an aftermarket, 4 into 1 that runs under the engine; making it the lowest point on the bike. The previous owner must have tried to Evel Knievel over some curbs or something, because the underside of the exhaust pipes were flattened, dented, and all scraped up. Rather than build or buy new ones, I decided to fix these.

The pipes are getting painted and wrapped with DEI Titanium Wrap, so I wasn't too concerned with the scrapes; just wanted to make the pipes round again. First step was to seal the outlet and install a male connection for an air hose.

This gave me a place to connect my air compressor. I would use the compressor and regulator to keep the internal pressure at 20 psi.

To cap the other end (without welding and damaging the sealing surfaces) I picked up a set of high temperature, expanding plugs from McMaster-Carr. I did have to cut a slot in the thread to get them really tight, but they worked great.

Next, I placed the exhaust in a vice and hooked up the air hose. I made sure the plugs were facing toward the ground in case one were to come loose. I slowly turned the pressure up to 20 psi, and sure enough, one of the plugs made a loud pop and shot into the ground. After a quick reset I was ready to go.

Once everything was holding steady, it was time for the torch. The idea is to heat up the dents and flat sections slowly and let the internal pressure push them out. This requires a lot of patience and experience with the torch...it's very easy to put a hole in the thin pipe. For that reason, I took my time, wore a face shield and lots of leather, and stood to the side of the pipe as an extra precaution. 

Here's a pretty good "before" and "after". The left pipe is almost done, and the right is still flattened out.

Another "after" picture with all the pipes treated. It's not perfect, but it removes the dents and flat parts well enough for pipe wrap...and keeps me from making new ones!