Upper plenum and exit air diffuser box

I spent a little time out at the hangar today and continued my work on the ducting for my relocated oil cooler. I’m making the new duct as a 2-piece part. The lower half will be attached to the cylinder baffles and the upper half will be a part of my fiberglass plenum. There was a pretty large volume of space to fill so rather than use 20 pounds of clay, I first filled the void with shop rags and then put duct tape over the rags so the clay wouldn’t stick to the rags.

With the rags and the duct tape in place, I started adding clay. It took me about 40 minutes to achieve this shape. As a little tip, it is tremendously easier to work with this clay if you first heat it thoroughly. I’ve got a microwave I use to heat my lunch in every so often. Turns out it heats the clay up fine, too!

Once I was happy with the overall shape of the clay, I painted it with 2 coats of PVA mold release. Again, it pooled in the low spot, but these dimensions aren’t critical to the thousandth of an inch so I’m not too concerned. It’ll just take a while to dry.

This is the plug for my oil cooler exit air diffuser box. Again, to avoid having to work with a 20 pound glob of clay, I started with a foam core. To help stiffen the foam up, you’ll remember that in a prior work session I coated the foam with a mixture of micro balloons and epoxy. This method seemed to work pretty well.

In the process of poking around the engine compartment looking for air leaks in my cooling system, I think I may have discovered the cause of my erratic CHT readings on my #2 cylinder! I’m not sure if this worked its way to being loose or if I somehow failed to torque it down, but this is how I found my #2 cylinder temperature probe when I de-cowled the engine. I love it when a solution is simple and obvious!


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