firewall corrosion

[vinceo]

Hello all,
My 1946 has a fiber glass looking insulation on the inside firewall that is falling away.
Looks like Cessna used some sort of glue to hold it on. There is residue of that glue
and some corrosion that was hidden by the fiberglass. I can pull the remainder of the
insulation off but how to remove that glue and treat that corrosion before it advances.
This is the second 140 with this problem that I have seen.

Any suggestions. I searched the forum but did not see any specific cure addressed.
Thanks

[6183]

You will certainly have a job ahead of you. No doubt throughout the airplane's life it more than likely spent some time outside in wet conditions, and that firewall insulation has held moisture causing the offending corrosion to develop. I would recommend that you do remove the firewall blanket material, and the glue to get at the corrosion affected areas. You might experiment with using some Citristrip Paint Remover available at big box stores (it's biodegradable and can be removed with water) to soften the glue in order to remove the residue with a plastic scraper. In order to remove the corrosion try using a small side angle die grinder fitted with a 3M Roloc attachment in order to use Roloc 3M Scotch Brite pads then followed by a good cleaning with some paint thinner. Finally, use some rattle can wash primer to spray the areas where you removed the corrosion. It will be a lot of tedious work, but it far outweighs removing the engine and then the firewall from the airframe to accomplish the job. On another note that insulating blanket helps keep out heat from the engine. Without it you might experience some warmer flights. Keep us posted

[vinceo]

I have now removed the old blanket entirely and scraped off most of the insulation backing
that clung to the glue. The old backing comes off in clods. I had to used a single edge razor
blade as plastic did not engage the offending material very well. In any case I am down to
the metal in some spots and glue in others. There is some corrosion in spots where the
aluminum surface has given way exposing the iron core and some rust. (Cessna calls it
"aluminized iron" in the owners manual).

In failed effort to remove the glue I have tried goo-gone, naptha, MEK, Kerosene and alcohol.
Nothing phases the glue with any significance. I am loathe to use some of this stuff in the
cabin but keep a fan blowing fresh air through to prevent harm to the fool writing this post.

I think I will give the Citri-Strip a try as suggested. Photos on the way as soon as I can remember
to bring my camera home for a download. This firewall corrosion is a situation that should have
been addressed years ago. I guess there are a lot of blind IA's out there.

[6643]

You could try acetone (will dissolve epoxy), just be sure to keep the fan going. Also vegetable oil.

[vinceo]

After much labor I am making some headway in cleaning the firewall. I did
try some citrus based paste that seem to help. However, some of the glue had
to be taken off by razor blade scraper and brute force. I have experimented
with side angle grinder with polishing pads. This works well, and a little too
well if you use anything but the very finest grit pads (ultra fine). Mostly I use
the grinder on the corrosion. I have the smallest grinder I could find. Just palm
size. The air hose makes it awkward and a bid dangerous to wiring, cables etc.
Getting those areas cleaned and finished according to 43-13 specs and Textron
Cessna Tech rep. suggestions.

Looking forward I plan to install Soundex fire resistant sound abatement to
inside firewall. FAA approved.

My firewall has several cables etc that penetrate the metal, as do they all.
I have removed all the grommets around cables and wires due to their great
age and debilitation. I am not really keen on replacing them with the
same material that will melt in a jiffy and really short circuits the whole
purpose of the firewall. However this is proving to be difficult finding
an actual fire resistant, approved replacement that is also anti chafe.

This is the most labor intensive and physically demanding aviation project
I have experienced. Makes crawling into the "Hell Hole" of a Bell 204, 205
212 etc child's play. Having said that I urge all you 120 &140 owners to
pull back your firewall insulation and find out what is going on there!
It may come as an ugly surprise! It is something your IA is probably not
doing on annual!

[6843]

Vinceo,

If your not a stickler for everything being FAA approved, I've used this with good results. I THINK it will give me better protection than a rubber grommet, but I haven't done any testing. It certainly can't be any worse than a dried-up rubber grommet. The description says its non corrosive to metal.

Dave

https://www.homedepot.com/p/3M-Fire-Bar ... 82#overlay

[vinceo]

I will have to give it some thought. Yes, cannot be any worse that what they approved the aircraft under.
There are some elements in the world of aviation that are imponderable.

Thanks