Filling oversize holes in firewall?

What do the veteran car-builders use to fill oversize holes in the firewall? I was thinking about having to use fender washers and weld them in and fill the center hole, but if there's something easier, let me know it! Some of the holes are oblong, too...

I use whatever hole saw size for cutting plugs then fill the 1/4" hole.

I'm not a veteran car-builder, but I just cut a plug out of scrap and weld them in.

Wow... that was a much easier answer than I anticipated... I have to stop over-thinking this stuff.

Easy to do man.....even for us old guys...

Coffee Freak said:

Wow... that was a much easier answer than I anticipated... I have to stop over-thinking this stuff.

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Easy template...hold a poster board piece up to the hole....tap around it with a ball peen hammer to use the hole as a cutter / punch more or less....then take it over to the metal and trace it , cut it and weld it in....works good for gasket making too ...makes nice clean holes without a lot of fuss...use the small end of the ball peen....lol

I usually take a piece of scrap metal and hold it with a magnet(if I cant reach to hold it) then mark and cut it out with tinsnips to fit the weld it up.

If the holes are not real big, some flat freeze plugs would work. Hold them inside the firewall, weld and grind. A little bondo if needed.
No hole in the middle to fill.

Sounds like a good way too....

RPM said:

If the holes are not real big, some flat freeze plugs would work. Hold them inside the firewall, weld and grind. A little bondo if needed.
No hole in the middle to fill.

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They do come in an array of sizes.......Good idea RPM...I like that...Sneaky your's is good too and probably easier than my idea...so there you go....CF...I think you have it....[cl

Savin Pennies

Had to fix some old mirror holes in a door the other day.
Princess Auto magnetic hooks from my wall along with a half dozen pennies seemed to work fine and made sense at the time. Instead of cutting little circles I just made some metal. Of course, after the magnets came off, I had to tap the pennies and they fell inside the door. Nothing a shop vac can not remove though. Of course the value of the build increased by 6 cents.

Cut a piece of metal that will cover the hole. You may need to enlongate the hole so the metal can fit in the hole and be turned.

Once you have that, weld a rod to the center of it. Either hold it your self or have some one hold it by pulling on it. Now weld it up, grind it and then fill it.

lungs

holes

You might try to use a magnet to hold the plugs flat from the bake side of the plate. It kepts it flat for tacking. Remove magnet before final welding. Hope this helps you out.[S

scrap metal and a magnet my friend, you can use tape.... but it smells horrible and of course catches fire.

Usually cut a piece of metal to cover hole. Tack a weld rod to it. Fish it through the hole and pull the weld rod so the piece is tight against the hole and weld away.

Lungs

I have a bunch of holes in my firewall, but instead of welding and hiding them, I'm going to celebrate them! Lol. Working in heavy industry has it's advantages.....we have several different styles of plug/cap/seal for electrical panels, operator panels,etc at work. You could probably buy them very cheap at any industrial electrical supply. I will take a picture of some of them tomorrow if you are interested. It'll be a whole lot quicker and easier than welding them.....imho anyway.

I use those thin metal disc's. That carpenters drive nails through.
I can't remember what they are called.
But I jb weld them in place and forget about them.
An added bonus
If later on I decide I need one of those holes after all
I simply pop it off.

Duck tap one side and skim the other side with bondo. NO no no! All the ways the guys said will work. I like to back up the plug with a copper,brass or alum bar. To prevent a backside blob ( stick weld) or wiskers from a mig.

As promised, here's some pics of the filler plugs I was talking about using....

BillM said:

As promised, here's some pics of the filler plugs I was talking about using....

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also the knockout plugs you find in electrical panels that look like coins [think they are called slugs ] come in different sizes

I just filled 44 holes in my firewall. Used all of the suggestions listed, depending on where the hole was and how big. some of the smaller holes I used the end of my brass drift to keep the fill from building up on the inside. You have to have long arms unless you do it without the floor...as I did.

weld on.......[