Tips/Q&A

Avoid costly exhaust cracks

by Dave Hamilton

All,

I want to share a few lessons learned from the annual condition inspection I am doing on my RV-8. This was my first homebuilt and I am still learning how to do things correctly. I share this information in the hopes that someone can be spared the expense, downtime and potential danger.

I found a large crack on the #4 exhaust. The crack began in the weld where the flange bolts to the cylinder and progressed down and around the pipe 180 degrees. I sent the exhaust back to Larry Vetterman for repair. Larry called me and gave me some much needed insight to exhaust maintenance.

The exhaust cracked in part because the slip joints and ball joints were frozen up. Larry recommends they be lubricated with “mouse milk” which is available at Spruce. Every time the cowl is off, reapply the mouse milk. These joints are there so the exhaust can flex. They must be lubricated.

I also hung my exhaust incorrectly. Mine was hung from the bottom of the engine case. I reasoned that the exhaust would move with the engine better and would be less likely to crack. In fact this resulted in a crack because the exhaust hangers were too far forward leaving too much pipe unsupported behind them. Its okay to hang the exhaust from the engine mount because the lubricated slip and ball joints will allow the exhaust to flex as intended. The front of the exhaust is supported by the flanges and the hangars need to go as far back as possible.

Now the BIGGIE! I have the heat muff that Van sells. There are two pieces on each end that fit around the exhaust pipe. They are connected by rods and then the muff wraps around these pieces. There are some hose clamps that hold the whole thing together. Mine never fit tightly. We NEED to file the holes where the rods connect to elongate them. Once these holes are elongated, you can get the heat muff to clamp TIGHTLY to the pipe. I remember my muff being loose on the pipe with the clamps as tight as I dare make them and the muff still fitting loosely. I reasoned that since it came from Van’s it must be okay. My heat muff has been chattering on the exhaust pipe for 230 hours. The exhaust pipe was nearly worn through! Imagine the consequences of a major hot exhaust leak there. Melted heater box and hot toxic blow torch at my feet? Fire? I have checked the heat muff on a couple of friend’s airplanes and guess what. Both were just as loose as mine and are likely wearing their exhaust pipes too.

Finally a plug for Larry Vetterman. He fixed my system for his cost and turned it around in 1 day. He called me to explain what I was doing wrong. Larry wants us all to be safe and enjoy years of trouble free service from his product once properly installed and maintained.

Ignorance may be bliss, but can lead to a very rude awakening!


Fraternally,


Dave Hamilton


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