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Dave's RV-7A Builder's Log
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Date:  8-2-2015
Number of Hours:  5.00
Manual Reference:  
Brief Description:  Exhaust and cabin heat

During my last session, I had test fitted the cabin heat muff on the #4 exhaust pipe, thinking it would be an ideal location. My logic centered on the fact that there are only two runs on the exhaust that are long enough—and straight enough—to accommodate the heat muff. The other location is the #1 exhaust, but that happens to be the farthest away from the air intake and cabin heat box. Unfortunately, my chosen location didn’t work due to lack of clearance between the top of the heat exchanger and the bottom of the engine case. Off with the exhaust in order to make the swap. While it was off, I used some anti-seize compound on the threads and then reattached with new lock washers.

The heat muff is a bit of a Rube Goldberg affair with two steel rods running the length of the exchanger and two end caps that hold the whole assembly together. The challenge is that these rods are conveniently about 1/8” too short to actually fit. The rods are threaded on each end, and the idea is that you screw a stainless nut down on each, insert the end into one half of the end cap, put the other end cap half on, then slide the whole thing into the exchanger with the goal to replicate the process on the other end. Sounds good in theory, but after about an hour of watching nuts and washer bounce merrily across the hangar floor, I came to a realization that I needed to trim that 1/8” off of the heat muff body in order to have enough thread sticking through to get a nut on.

Over to the belt sander, and in a couple of minutes I had hope that it was going to work. That couple of minutes turned into another hour, but in the end, I was able to get the whole assembly together. I get the fact that this is supposed to be somewhat airtight, but certainly there is a better solution…it literally took me three hours just to get this all together. Finally, I cut the scat tube and did a test fit. I’m going to need to trim them down and protect them from coming into contact with the exhaust, but that will be another day.
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This is how it starts...

This is how it starts...

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And this is how it's supposed to look...I think...

And this is how it's supposed to look...I think...

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Test fitting the tubing

Test fitting the tubing

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