The original :legal: clamps that hold the muffler onto the exhaust stacks are known to be quite flimsy and are supposed to be loose to allow for some thermal expansion movement but are quite often a nuisance. I have tightened them several times, replaced the bolts with 1/4" Incolloy bolts and nuts to prevent corrosion, and the muffler is always loose. This looseness and the thermal expansion causes the left side exhaust stack (the longer one) to bend outwards and very soon the cowl reinforcement bow is cutting a hole in your heat muff skin.
The next thing I tried were automotive muffler clamps ( between annuals ), They are steel, they rust and they create a groove in the muffler flanges and make the problem worse. I have now found a better solution and it is a pair of Harley Davidson Aircraft Style muffler clamps available on Ebay. After all, they are aircraft style... There are several kinds and they mention all the measurments except for the diameters. They need to be 2 1/4" open and less than 2" fully closed. They are sold in pairs for about 12 bucks. One style is a solid steel ring about 1/2" wide with two bits of pipe welded on the top and a 1/4" allen bolt through it. They are chrome plated. These are too narrow and need to be filed so they close tight enough. I had better results with a second type that is about 1 1/2" wide and looped on the ends with crossbars and a single 3/16" bolt through the bars. Being wider makes the muffler flange tighten better over the ends of the pipes and prevents all movement when tightened up. Having the muffler and stacks all tightened into one assembly has not created any problems so far with thermal expansion, the muffler tailpipe is no longer eating my lower cowl away, it is quieter and there is no carbon monoxide escaping through the connection. They also eliminate a flame path in this area that is frequently doused with oil and gasoline fumes specially after priming... I showed them to my A&P (who is also chief inspector for a major airline), and he gave it his seal of approval. According to him, on an aircraft built in 1946 when there was no such thing as an STC, anything you come up with that is proven better than the original equipment is an improvement. If the original parts are no longer available or hard to obtain, you are allowed to improvise. A logbook entry would be good, a field approval could be done, but he suggested first sharing the information with the ercoupe group to gather collective experience and recommendations and make it a type class recommendation so everyone can benefit from the improvement. I have been testing these clamps for almost a year now and they have not had any adverse effects on anything. Your comments are appreciated. I will upload pictures ( when I figure out how), to better identify the clamps, I feel my description may not be good enough. Alan Fairclough N87333 N94694
