by Ron Hogan
I fly a modified Fly Products machine with a Black Devil engine on it.
Recently I had to take my muffler apart and thought I would share the info and pictures with others, incase someone else ever had to do it.
After a flight, I did my post flight check and noticed that one of the three nuts was missing off my muffler. When I looked closer I saw that not only was the nut missing, but also the complete stud that the nut goes on was missing.
This is known as the flange in the 1st picture. There is a new updated flange, which you can see, in the 2nd picture. The ring helps to keep the nuts from coming loose by bending the fins till they touch the nuts.
The Black Devil exhaust system is actually three parts. The Manifold, tuned pipe and lastly the muffler/silencer, which we are concerned with in this article. With some direction from Mr.Oscar Meschiari at JPX Italia I proceeded to repair and replace the broken stud.
I had to take the cover/tube off the muffler. To do this I had to remove the nuts, then drill out the one rivet that held the cover/tube in place. The rivet is located at the end of the cover/tube near the muffler output flange. In this picture you can see the hole in the cover/tube where the rivet once was, the flange and gasket.
Once the rivet was removed I slid the cover/tube off. Some come off easier then others. As I slid it off, it revealed the inside of the muffler including the sound dampening insulation as you can see in the next two pictures.
In the next three pictures, you can see where the stud is broken where there should actually be three studs. The studs are really just bolts that are tack welded to keep them in place and disabling them from moving when you tighten the nuts.
I then took a dremel with a cutting attachment and cut off the old head of the bolt that was broken. Make sure you cut it off evenly, so when you put a new bolt on it will sit flush. There was only two tack welds on the bolt head that needed to be dremeled. I then took it to a welder where he Tack welded the new bolt head in two places (I put a nut on the bolt so that it would hold the bolt still and even while the welder did his work. This assured the bolt/stud would be even, so the flange would fit over it along with the other two studs).
From this point I put everything back together, including installing a new rivet in the tube. I put a good coating of Hondabond where the flange mates to the studs. After the nuts were tightened, I added red paint on the nuts where they make contact to the flange. As Alex always says, "this makes your preflight go faster". Just look to see if the paint seal is broken. I also added a good dab of high temp silicon to each stud to absorb vibration.