Inspecting the firewall - 2 hours

Now that I've had time to let things sit and I can now really look at things. I'm really becoming uncomfortable with how the firewall looks. When you really look at it, since that sealant is soo thick, I fear that I do not have a good solid mechanical connection between the pieces.

After much swearing, looking, head scratching. I decided to drill out this connection to get a better look. It ends up to look much worse than it really is. Where the parts actually mate, the sealant is very thin. however, by drilling/punching all the rivets out I'm quite concerned that the rivet holes are too opened up/sloppy.

Being this is a major connection/stress point for the engine. I've made the difficult decision to abandon this fire wall. I will have to order a whole new firewall, but it isn't cheap and I have no money for new parts right now.

This build is put on hold for a while.     

Replacing rivets in the firewall - 8 hours

In the craziness of yesterday, some of the rivets need to be redone. drilling the heads off is easy enough. But I am dreading punching them out of such thick material. So... I cut a piece of oak that and fashioned it so that it would support the firewall when I drove the rivets out of the firewall.

This actually turned out to be an incredibly good tool. This gets placed under the firewall assembly and the rivet head gets placed inside the "notch". It then is able to support the area as you punch out the rivet.

I use some oak blocks under the firewall to support the 3 corners that I am not punching the rivets out on.



All done

Riveting the firewall - 14 hours

Before we go on...Lets just be clear. I have found out the hard way this is NOT HOW YOU SHOULD COMPLETE THE FIREWALL. Read on and learn why.


Super long day of work with not as much progress as I would have liked. Just a very fussy process.

First order of business was to apply a thin layer of sealant as a fay seal between the aluminum and the firewall. Now...I had it in my head that this would go easily, but let me assure you it is not. The sealant is extremely thick (much thicker than proseal) and it takes a considerable amount of time to put it on the angles and get it thin with a plastic scraper. I should have stopped at this point.....I didn't

I continued on.... I began to worry about the silicone setting before I could rivet it. So I felt it wise to clamp some of the more important areas.  This process becomes extremely difficult as it is vital to cleco the pieces to get it tight, but you cannot back rivet with the clecos it.

I just kept going.

And going...

It was nearly 3am I think when I finished... Some of the rivets will need to be re-done. I worry about it tomorrow. 

Getting ready to rivet the firewall - 2 hours

I have been deliberating quite a bit this last while on how to use fire barrier with the firewall. Talking things out with a friend we reasoned that it was a good idea to place a small film of fire sealant between the aluminum angles and the stainless steel firewall. The thinking is that if the aluminum rivets melt away in an emergency, there is some protection there for the fire barrier to do its job and close the rivet holes off. As well we were discussing the fire barrier would act as a good means of protecting the aluminum from corrosion as we didn't feel it wise to prime that mating surface.

Also in the research, getting CS1900 firewall sealant to Canada is not easy. Frankly it is darn near impossible. After lots of research, I ended up accepting the fact the only project I can get in Canada is 3M Fire Barrier 2000+ through aircraft spruce. Its the only "high end" fire sealant they sell.

So tonight, I spent some time getting things all set up and ready to go as I will need to finish riveting as fast as I can as I will be working on things "wet"

Engine mount bracket fit - 3 hours

One of the items I notice some have struggled with on other build logs was to get the correct placement and fit between the engine mounts and the longerons. Seems the margin for error here is a bit tight. So as I typically try to do on parts, I marked out edge distance on all of the engine brackets first. Here I used an edge distance of about 0.025". It gives me a bit of a buffer rather than using the Mil-Spec minimum of 0.0219" (The buffer is always a good thing).

After marking things out. I placed the engine mounts to check fit (but not to drill just yet). Initially the fit is ok, its just on the line...



I've used some clamps to get things help in place. When I really look at it, it looks like things can get just a tiny bit better. There is still a small gap between the aft most flanges of the engine mount that I can tighten up. So I dug out another small clamp and clamped the mount vertically as well.

This snugged up the fit just a bit better and allowed for much more edge distance. Looking really good now. Plenty of material to work with on those mounts.

Fitting the firewall - 2 hours

I need to set the firewall in place to begin checking fit and alignment, but I was scratching my head on how exactly I was going to do this. Borrowing an idea I seen on another build-log, I used the ironing board (with some help) to get it to the right height.

At this point I can start checking center, alignment, etc. I still need to trim back the longerons just a bit but I will wait until that becomes critical.

Drilled the longerons fwd of F-704 bulkhead - 6 hours

A big item on my to-do list is to finish drilling the longerons forward of the F-704 bulkhead. I've put this off for a couple of days thinking how best to do this. I want to ensure that the longerons are even on both sides. I fear that if I just go ahead and drill them they may not be exactly aligned, even crooked. I finally decided that I need to temporary install the firewall. I used the ironing board to support the weight and clamped/secured it.

I drew centre lines all down the firewall and down the centre of the bottom skin.

Then I set up the laser level and began checking everything. Some very small adjustments, but I was happy that both longerons where sorted. This was a very tedious process I might add. I began drilling from the F-704 bulkhead forward alternating sides. I finally reached the #30 holes and I marked them with a sharpie to double check edge distances. All good!



I finished drilling the longerons. Now I just need to trim them back 3/4" from the forward edge of the skin. I'll save that for tomorrow.


I need to get the F-904L attach strips cut. Reading other build logs edge distance is a possible concern here so I just used the full 3" lengths that came with the kit. Ill drill them first and then cut after to ensure edge distance is not compromised. I checked the fwd pieces and marked them to be cut at an angle so that they will nest into the longeron.

I started to carefully mark and drill my holes. I also rounded the bottom edges to nest into the radius of the longeron.

As you can they are very long. The aft pieces will allow me to drill an extra cleco at the top.   I will trim them down. The blue line represents 2 1/16" however that is too close to the rivet hole so I scrubbed that line. I'll do some checking on build logs first, but I will likely leave a good amount of edge distance and go a bit longer than the 2 1/16" dimension.