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I just got done setting the cab back on my truck chassis after replacing the firewall and many other panels. I used the Bitchin Products smooth firewall with a 3-inch setback for a big-block, hoping my three carbs would clear the firewall. It's just a little too tight. I have some choices: change manifolds (and I'm not going to do that), cut an opening in the firewall and weld in a pocket, or do what I have seen on some of the TV hot rod shows, where they make a blister by heating a section red hot with an oxyacetylene flame, and smacking a pocket into it with a hammer. Can you give me any advice on doing this, and how to keep the warping down?
E. Molene, IL
Well, it looks like your air cleaner bonnet has a little clearance already, so if you give it 1/2-inch more clearance, that should be sufficient. There are many ways to do this, but I don't recommend the "heat it and bash it" technique. It's not that you can't do the job that way; the problem is that both the heating and the bashing will distort the panel next to the blister. It's nice and flat now, and the job will be much neater looking if you keep it flat!
Here is an air cleaner that doesn't have enough clearance with the firewall. There are dif
I'd start by cutting a round hole in the firewall, centered on the point that's closest to the air cleaner bonnet. Then you can make (or find) a domed piece of steel to fill the hole. (Hint: Many commercial kitchen supply stores have ladles and woks in a variety of sizes-I'll bet you can find one exactly the contour required for your job.) If you hand-shape the blister, you can form it from a round disc of steel sheetmetal worked to the proper shape with a mallet and sandbag, or even by hammering it into a block of wood with a shallow cavity carved into it. Once you have a properly shaped blister, you can simply trim your blister to size and weld it into place. One further step you can take to keep the distortion down (and to make the job look more finished) is to use a hammer and dolly to form a slight curl on the edges of the opening before the blister is fitted into place.
Be sure to double-check everything after the blister is tack welded-you don't want to discover that you'd like just a little more clearance after the welding is done!
I have seen some of your DVDs on metalshaping, and it looks like a lot of fun. I'm eager to try my hand at it. I was very encouraged to learn that you can make complicated sheetmetal parts with some very simple tools. I have a couple of hammers and dollies, and an oxyacetylene torch already. I plan to get some mallets and a sandbag before I try my first metalforming project-a hoodscoop for my El Camino.
My question is, what do I fill my sandbag with? Of course, sand being the obvious answer, but there are many kinds of sand-what is the best type to use for a metalforming bag? Is there any benefit to using steel or lead shot over sand?
Via the Internet
Almost any type of sand will work in a bag. I generally use silica sand, and I've found that the coarser the grain size, the less the sand tends to displace as you're working into it with a mallet. If only fine-grained sand is available, that will work OK, but you may have to shake the bag from time to time to redistribute the sand.
Both lead and steel shot are heavier than sand, so they displace more slowly, and this does offer a slight benefit, since they won't need to be shaken as often as sand-filled bags. They also weigh considerably more than sand, which may be a disadvantage if you need to move the bag frequently.I sometimes use a bag to weight a panel down to my workbench, and a heavier bag is useful for this application.
Although steel shot works well, it can sometimes rust and clump together in humid climates. Lead shot doesn't rust, but unfortunately, it is a somewhat toxic material, so you might question whether the potential health risk of handling it is justified. It's also quite expensive these days, and it's becoming more difficult to find because of the environmental issues associated with lead use. Many gun reloading supply stores now sell shot made of bismuth, which is similar to lead, but doesn't have the same degree of toxicity.