Before fuelproofing... I mark prop-shaft centerlines (both vertical and horizontal) on the firewall. Then I write (fine point sharpie) the motor thrust angles on the firewall as well. Careful not to write where drill holes are.

Then.. mix up 30 minute epoxy. With a heat gun the epoxy mix thins to water consistency, and spreads very well. It dries nearly clear, leaving all the marks/writing I made earlier permanent.

Even if you spread the expoxy into the fuel line holes, and it builds up too much to get a fuel line through... you can always run a drill through it again to clear it out enough... Even though the heating/thinning may weaken the strength of the epoxy, you're using as a sealing agent, not as a structural enhancement..


I tried fuel-proof paint on my first plane... yuck... wouldn't cover, needed several coats... Not worth it... The near clear epoxy looks way better.. IMHO....

Picture: Even though I built this STM for electric power, I fuel proofed the firewall and engine bay. I really think making center lines, and writing down thrust angles is a good idea.. Even if I do say so myself...