Hello-

After putting about 7 flights on my H9 J-3 Cub PNP, a member of our local club recommended that I fuel proof the firewall with some epoxy 30 and 90 percent alcohol. Because I have flown the plane without the cowl in order to adjust the engine, a small amount of fuel has already found its way onto the firewall. Our club member recommended the following:

1. clean off the fuel on the firewall using 90 percent alcohol and let it dry
2. once the alcohol dries, mix epoxy 30 and 90 percent alcohol and apply a thin coat to the firewall


Does this sound about right?

Thanks!
Bjfrankl

Yep, mix some 30 minute epoxy and add a few drops of alcohol to thin it. I also do any and all exposed wood under the model all the way to the tail. Exhaust can get in everywhere. Do the fuel tank area very well too, (I do two coats) because if you ever have a leak it will save you a lot of grief. I usually do this when building, easier to get in to places. Better late then never though.

I would be very surprised if the firewall on a Hangar-9 plane was not already fuel proofed when you get it.

I thought that the firewall may not have been fuel-proofed because a cowl is placed over the engine (although I suppose a cowl doesn't prevent fuel from getting onto the firewall). I prefer not to fly with the cowl, so I thought that I would fuelproof it with epoxy 30.

I called Horizon Hobby today, though, and they said that it has already been fuelproofed.

H-9 planes have fuel proofing on there fire walls, just because it has a cowl has nothing to do with wheather or not its had a coat of fuel proofer added.

now if you wanted to add a little extra there's nothing wrong with that.

after removing the engine mount,dip the mounting screws in some Vasoline and screw them into there locations, apply epoxy to the firewall and use a heat gun to warm the adhesive this will thing the glue to a nearly water like consistancy then brush it out to cover the wood after its dry pull the screws and reassemble simple as that.

this also works for the tank area,as a side note I like to nuke my epoxy, pop the tops off the epoxy bottles, so they can vent a bit, and place them in a micro wave on med. for about 5-10 seconds this will thin the 2 parts, allow to cool slightly and mix them the thinned mixture can be painted into the tank area,in a tight spot it can be poured into the tank area, and the fuse can be rolled so the glue can get into the nooks and crannies, this also works well for fuel proofing.

it also helps strengthen the joint between the firewall and fuse, use at least 30 min epoxy if you heat it since warming the glue speeds up hardening times

I will probably just leave the firewall as is since it sounds like it is already fuelproofed. However, I have two small holes in my firewall because my buddy and I redrilled the hole for the throttle pushrod. We didn't like the pushrod's angle to the engine (the pushrod brushed up against the engine when I advanced to full throttle). I may fill the hole with epoxy 30 just to seal it. I can't think of anything better to seal the two small holes with.

Thanks!
Bjfrankl

depending on how big the hole is take a small piece of wood and epoxy it into the hole, then cut the wood with a exacto knife and a dab of the glue on the area will seal it from any fuel.