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Dave's RV-7A Builder's Log
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Date:  1-21-2017
Number of Hours:  3.00
Manual Reference:  
Brief Description:  Exhaust hanger installation

Short session today devoted to removing the original exhaust hanger arrangement and starting to work on a way to redo it. Based on my reading, the exhaust system is very prone to developing cracks if the hangers are attached to the airframe rather than the engine sump. This is due to the fact that during start up and shut down the engine actually moves significantly as the torque changes. That movement is generally absorbed by the engine mounts. If the pipes are directly attached to the airframe (or even engine mount), some of this movement can be transferred to the pipes, and ultimately cause cracking.

The solution is to attach the vertical exhaust hangers to engine sump bolts, and the horizontal hanger (more of a spacer actually) between the vertical brackets. The whole affair is a bit complicated looking, and to make matters worse, on an A-model RV-7, the nose gear support structure is very much in the way. The other challenge I faced was that during initial installation I was not 100% aware of the problem of installing the hangers on the engine mount, so I had trimmed part of the steel tubes that form the primary attach points. Confused yet?

With all that, I needed a way to lengthen the hangers, so I evaluated using 3/8” aluminum rod (rejected since it was too hard to fabricate attach points) and finally settled on buying some new reinforced rubber tubing and use the current stainless steel attach brackets. Off to O’Reilly’s to buy some fuel line—yep, that’s what the exhaust manufacturer supplies in the hanger kit. Go figure.
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The black tubing is the hanger, you can see the marks on the mount where it was formerly attached

The black tubing is the hanger, you can see the marks on the mount where it was formerly attached

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