The Thermo-Tec heat shield needs to have its edges sealed to prevent any fluids from being absorbed into the matting that’s under the foil. One of the options is to use 3M aluminum foil tape. Aircraft Spruce sells it in various widths, I decided to use the 1.5”. Applying it was easy, just cut to length and press to seal. I did round the corners to match the matting corners to make it look more aesthetically pleasing.
I found out that my measurements for the engine cowl were spot on once I was able to install the propellor. That was a huge relief as there are several moving parts that affect how the cowl sits and going by just measurements was a little scary. I was now feeling comfortable in finishing the inside of the engine cow which consist of sealing the fiberglass and installing heat shielding. I decided to use a product from Rhino linings called Rhino 9700. This product is used by composite airplane builders to line the inside of their fuel tanks. It is a two part epoxy coating that drys to a glossy light grey. The process is pretty easy, clean the cowling, mix part a with part B and apply within the 25 minute time period. You should only mix enough that you can apply in that timeframe as it starts to set up fairly fast after that. Are used a small paintbrush and a foam roller to apply, it didn’t make it perfectly smooth but it was close enough for the inside of the cowl and my needs.
It is dry to the touch in 6-8 hours and fully cured in 7 days. Now the cowl will be protected from oil, fuel and any other liquid in the engine compartment.
So over the last month I have been slowly working on the engine cowl surface’s starting with the insides first. I had already started the inside prep earlier so it was a good place to continue. The process was to sand the surface smooth but not break through the epoxy. Once it was smooth and all the ridges knocked down I applied a layer of epoxy on the entire surface using old hotel key card to squeegee the epoxy into the holes. This allows you to remove any excess epoxy which makes future sanding much easier. I would then let the epoxy cure overnight so I could repeat this process. I did this a total of four times on the inside surface for both the top and bottom halves. It’s time consuming since you have to let the epoxy cure and then the sanding, I have learned to hate sanding! I filled in some of the larger imperfections on the inner surface but not getting too crazy as it’s just the inside. The idea for me is to get the inner surface acceptable to paint to keep oil, grease and any other contaminant to be easily identifiable and cleanable. Also most of the inner surface will eventually be covered with an aluminum foil type material that radiates heat from the exhaust system and protects the fiberglass. There are various brands of this heat shield and I have not decided on which one yet. Once the insides were good enough I moved on to the exterior surfaces. The process is the same and just as the inside except I added an additional step. This was to use UV Smooth Prime to fill in all the tiny pin holes. This primer is like paint with drywall mud mixed in. You really have to mix it well. It’s so thick I decided to buy a paint can shaker from Harbor Freight Tools to handle this. As of today they cowl halves are 90% done and I’m just finishing up some small imperfections that are left. Here are a few pics of the process but not much to show while sanding.
The last part of the baffle puzzle are the lower cowl lip seals. These get attached to the lower inlet lip of the lower cowl and create a seal against the inlet ramps on the left and right sides. The idea is to shape strip of aluminum to the shape of the inner shape and use it as a clamping surface to squeeze the seal fabric in place. I worked the right side first and bent the strip to the shape making sure that it had a “clamping effect” to the sides. I then cut a piece of the 3″ wide seal longer than needed to start with. I then laid out three screw hole marks for the screws that will eventually hold them in place. I then drilled the three holes in the cowl flowed by match drilling through the cowl into the aluminum strip under. I used these holes and marked the seal fabric so I could punch holes it the fabric as well. With all three parts now having holes in them I attached them to the cowl. The fitment is just a rough shape at this point and need to be trimmed to fit better. I decided on 1″ as my overlap which should be sufficient. I marked 1″ marks along the entire cowl lip for cutting. I removed the cowl and the baffle and trimmed along the marks I made and put it all back together. I’m supper happy with how the fit was after trimming. I put the top cowl in place to see how the fit was and it ended up very tight and should provide a pretty good seal. I repeated the process on the left side. I returned the baffles to the forward center section as well as the forward sides and installed the top cowl. Here is how they look and I’m pretty happy with the fitment. The left side doesn’t have rounded corners due to the air filter placement. In the corners there is a little gap that will allow leakage.
I removed the lip baffles and drilled, deburred and riveted nutplates in place for #8 screws. I’ll install these once all the cowl work is finished up.
While waiting for some fiberglass to cure on the lower cowl lip I decided to fabricate the hidden oil door hinge pin. The door is hinged on the top with a hidden bracket. To hold the bottom of the door I decided to use another piece of hinge. I installed these a long time ago and had planned on how I would remove the lower hinge pin to allow the door to open. The upper bracket has a spring to it so when the door is unhinged it springs open. So I had fiberglassed a aluminum tube with the same inner diameter of the hinge itself to the inside of the cowl to direct the pin as it’s inserted to the first hinge eyelet. I used the hinge pin to mark the firewall where I needed to drill a hole for the pin. I used a dab of orange torque seal on the tip of the pin and slid it through the hinge eyelets until it touched the firewall and left a dot of torque seal identifying where to drill. After removing the cowl I drilled the hole and clean the edges as the stainless steal is very sharp after drilling. I returned the cowl and slid the pin to make some marks for where to cut and bend for the handle I was planning on forming. With the cuts and some bending I made what I think will work well. I put some shrink tube on the handle side to keep it from scratching and make it easier to hold. I only have to pull it out far enough for the door to open and check the oil. Then while oblong the door down I slide the pin in and the door is secure. I made the handle long enough so that it can be tucked next to the nylon block for the baggage door lock. This will keep it from spinning around in flight and the baggage door itself will prevent the pin from sliding out of position.