Aimable Heat Duct?

[jetdriven]

Those valves have a sliding piece that is supposed to cut the hot air off from the muffler. We found that there’s no amount of fiddling with this to keep them from leaking. However the 1979 and newer airplanes have a different type of valve, it is actually a round plate that swings on a shaft and covers the end of a tube. Putting some fresh 1/32” thick silicone rubber on the end of this round piece inside, seals off air super tight and no heat leakage.