I called another builder friend over this morning to help run the rivet gun while I bucked. There are 4 pre-punched and dimpled holes that would be used for the exhaust ramp in and RV-8 but the -8A does not use them. I wanted to fill these with rivets before the engine mount goes back on.
I next turned my attention to the eyeball firewall pass through I am going to use. These are all steel and allow the cable to exit the firewall at different angles. The control cables from Van’s are about .330 in diameter and the closet pass through I could get was .260 but you can drill them to size, which I did with one on the drill press.
I have 3 of these to install so I decided to make a template for drilling the 6 mounting holes. I just used some spray adhesive on a scrap piece of aluminum. The firewall comes pre-punched with 7/16 holes, I put the same size hole in the template I made, and then used a Sharpie pen to hold the template centered.
Next was to drill out the center hole to 1 1/8. Now if there were not a large hole there already I would use a punch set to punch the hole to size but I thought a punch might mar up the firewall if it were not solid. I used a step drill which was a real pain after about 7/8”. The firewall is so thin that the step bit would catch and then twist the firewall. What finally worked was to drill the hole close then use a file to smooth it to final size. I would also install the pass through backing plate, this helps stabilize the thin stainless firewall.
I am happy with how they turned out, I still have to decide on the third hole, the kit comes with a small hole outboard of the two you see but I think I will wait till I can hang the engine on a hoist near the mount to see where I would like the prop control cable to come out. There is a pre-punched hole above the throttle and mixture that is meant for a firewall mounted brake fluid reservoir, I am going with pedal mounted reservoirs so I might be able to use this hole.
Note hole above might be an option for 3rd cable, plans call for the small hole on the right.
