Flying Information

How to remove the "Gunk" from your muffler.

By Mike Fortune

   There is nothing that makes a model look more neglected than the "Gunk" that accumulates on the muffler. The problem is now that it's on thereÉhow do you go about getting it off? Well, before we try to remove itÉwe need to know what it is. Our model engines run on what we call "Fuel":). Fuel is actually a blend of several basic components: alcohol, nitromethane and oil. The alcohol and nitro are there to promote combustion, make the engine run and produce power. However, with just these two components the engine would run for just a few seconds and the engine would be a total loss. At this rate, none of us could have ever learned to hover! Someone figured out years ago that adding oil to the blend made the engine run better and longer! However this came at the expense of loss of horsepower. Now, when all things were considered, this loss was actually a long-term gain as our engines last longer and are more reliable.

   Well, with this new blend (Alcohol, nitro and oil) now in hand and long engine runs now possible, a new problem occurred (Isn't that just like this hobby? You over come one problem only to discover another!). During these extended engine runs, the muffler was now getting hot and the exhaust from the engine seemed to hang in the air. Soon after this we noticed the once shiny muffler had started to develop a really bad case of what looked like freckles (known by arteests as a "wonderful patina" -ED).

   These brown stains seem to be everywhere on the muffler and some even on the engine. Soon it was discovered that these spots were only occurring after we added the oil to our fuel blend. While the alcohol and nitro actually burn inside the combustion chamber, oil, for the most part, does not. The oil is the primary component that is passed out the exhaust having previously lubricated the all the moving parts and providing cooling for the engine.

   OK, now that we know what it isÉwhere does it come from? Why are certain areas of the muffler darker than others? Most of the time the darkest areas are around the portion of the muffler that bolts to the engine. Why? This is the area that is hottest and also where the muffler and engine join together. It is at this joint where leakage can occur. Any leaks in this area are quickly deposited on to the hot muffler. At this point the leaked oil is actually baked on to the muffler.

   So, now that we know where it comes from, how do we prevent it? The joint between the muffler and the engine must be sealed. I have read many suggestions concerning how to seal this joint. I've heard of guys suggesting the use of epoxy, gaskets, silicon sealant, JB weld, and card stock. My personal favorite was that of silicone sealant. I just put a gob between the engine and muffler and hoped for the best. This was always met with mixed results. Sometimes it worked and sometimes it didn't. I have tried all these other methods, with the exception of the epoxy, but I continued to have leaks at this joint. It was after a conversation I had with Wayne Mann on this subject that I adopted this secret of sealing the joint between the muffler and the engine. Here's the equipment: a piece of glass, sandpaper and oil. Here's what to do: Lay the sandpaper (400 grit, good quality wet/dry type) on top of the glass and add a few drops of light oil on the sandpaper. Next, moving only in a figure eight pattern, sand the muffler flange until it is perfectly flat. You should see a nice even flat surface on the face of the muffler flange. After carefully plugging the exhaust port (Or preferably, with the engine completely disassembled), repeat the same on the engine exhaust port. Again, you should see a nice even and flat surface on the engine exhaust port. Next, clean this area with a good degreasing agent. I use paint thinner. Now, apply a very thin coat of blue silicone sealant to the muffler flange. This should be thin enough that you can barely see it on the muffler flange. Now, join the two as normal.

   Sanding the two on the glass gives a smooth, flat flange surface that has very fine texture: "swirl" grooves from the sandpaper, that is otherwise hard to duplicate. The joint is so tight now, hardly any sealant will be left in the joint itself. The swirl texture actually helps hold the silicone sealant in place and resists any blow out occurences. For those running muffler pressure, you should see a more reliable and constant fuel mixture as the muffler is no longer losing pressure during the flight.

   So now that we have the leak sealed, how do we return the muffler back to its once beautiful shine? There is a product for this that is called Simichrome. It comes in a small tube and it cost about $5.00. I bought this tube at a local motorcycle shop. ItÕs truly amazing how effectively this product not only removes the "gunk," but also polishes the muffler at the same time. Not only is it effective, but also it's also quick! It takes just a few minutes to polish an entire muffler. It comes in paste form and basically is rubbed on and rubbed off. (See box label for a more precise description.) For those of you wanting to remove the "Gunk" from your muffler, give these methods a try.