In addition to the ones marked in the picture, there are also some on the sides of the firewall that have to get removed but I forgot to take a photo before I drilled them out.
Here is the "after" shot:
This one shows only two of the four rivets to be removed on that FW side. The next two are the ones under that goop (not visible) that right above, on the vertical part of the firewall, the drilled out aft rivet.
After you have removed these, you ought to draw line in the shelf between the two rivet holes.
This line will later be used to match-drill holes through the shelf into the stiffening angle underneath.
But first I had to remove the existing diagonal stiffener angle on the side skins. Van's asks you to cut off a portion that will interfere with the installation of the additional angle inside the fuselage. That's what they had you drill out the upper 3 rivets on the side. However, this approach appeared to be rather hard to turn into anything good. I foresaw the cutting wheel run off and gut into the painted skin and I could not even image how I was supposed to deburr that mess working under the instrument shelf.
So I decided to remove the angle completely, cut off the upper part with the bandsaw and correctly deburr it before riveting it back in place.
The upper 1" or so had to get removed on the side with the little fin.
No way I could have done this working under the shelf!
Reinstalling it did not take any time worth mentioning either.
Back to the instructions. I had to cleco the additional angle in place, check for clearance and proper alignment. Here you see why I had to cut off a part of the diagonal stiffener:
The aft end positioning in the above picture is not perfect. When I drilled the first hole I pushed the angle up a bit before drilling and it turned out just as requested.
I used my iPhone for these inside shots as it is easier to handle than a full-blown bulky camera. After the angle was properly aligned, the rest of the holes were match-drilled from the inside through the skin and clecoed.
This is how it looked on the inside.
But that is not all yet. I had to extend the line of rivet holes on the side skin with a marker to extend all the way to the front end. The hole spacing was 1" so I made my marks, pre-punched and drilled the holes into the angle. This time from the outside. After that the angle gets removed for deburring.
I decided to prime the forward part of the angle that would contact the stainless steel of the firewall shelf. The rest of the possible contact surfaces is painted so I did not bother.
While the primer was drying, I moved on to the right side and removed the diagonal angle.
The fin was quickly removed and the angle deburred and reinstalled. The additional stiffener angle was installed and aligned and the aft most hole match-drilled.
I should have given the iPhone more time focus before taking the shot but you can still see the proper alignment with the existing rivet. All the match drilling followed and this time I did not forget to take a photo after marking the hole line extension and doing the pre-punching.
All went out for deburring and priming again. While the primer on the right angle was drying I started riveting in the left side stiffener.
No surprises while riveting. Some of the rivets are hard to get too though. You do need the close quarter riveter as well as a wedge tool to do a good job. I should have mentioned that you need a 12" #30 drill bit to drill out some of the rivets on the shelf. Those are the same ones that need special care during riveting as you probably guessed.
Once the left side was done I declared the primer for the right side dry enough and installed that one as well.
Again, no surprises.
From the inside the stiffener looks like this:
It is recessed so far that I also did not bother painting it to match the interior. You can hardly notice this thing.
All in all, the stiffener kit took me 7.5 hours to complete. Not a big deal but I also did not have to remove the lower cowl as it was already off. And I am not fully done yet as I need to get some additional Pro-Seal to cover up the newly installed rivet heads.
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