Don't get the concept of "stretched" metal? Try pushing a very large dented area back out to its former profile. Much of the time you'll push the dent out, and it will spring back into the dented configuration. This is "oil canning," and it happens because the impact of the accident has stretched the metal over a large area. The corrective method for this type of injury is to heat-shrink the panel, which we'll learn later, but the important thing now is to realize that if you don't use patience, you're screwed. So take it slowly.
See there," said Roy, pointing to a crushed place on the roof of my formerly rusty-but-straight BMW coupe. "That's where the chain came across the top...and after I told 'em not to." I'm having real trouble controlling a couple of urges: I want to sit down in the middle of Roy's dirty concrete floor and cry over my trashed classic...and at the same time I want to hitch every employee in the damn place to their own chain hoist and dunk them in those gawdawful paint-stripping pickling tanks for a few hours. Not too long, just until the bones show.
I must now confess. When I suggested that sending a car to the paint stripper was an alternative preferable to doing the dirty work yourself, I was speaking from a position of total ignorance. Now I know different. Now I have deduced how this paint-stripping game works. Apparently, from the looks of my coupe, the method these people use is to chain the car to a large construction crane, hoist it 306 feet in the air, then drop it onto a large concrete slab. This process is repeated for several hours, until every scrap of paint has been slammed loose from the unrecognizable ball of metal that used to be your classic car. The cretinous swine who perpetrated this atrocity have struck before, and they will strike again. Beware. If anyone suggests that you trust your car to the heinous thugs running a paint stripatorium, run away. Run away fast. But if you took my initial advice and sent your irreplaceable sheetmetal masterpiece to such a facility, never mind. It'll probably be just fine. Sure it will.
After I finish agonizing over whether or not to do the humane thing and crush what's left of the coupe, I decide that I might as well go through the rustproofing motions, just in case. Know that if you've stripped paint from the car with a chemical stripper, you have about 6 seconds to treat it with rust preventative before it turns brown and disintegrates. So, with great dispatch, I trailer the remains home, purchase a gallon of phosphoric acid (otherwise known as naval jelly) and use a garden sprayer to hit every square inch of the coupe with this vile liquid. After the phosphoric acid spraydown, I rinse the car off. I now have approximately 13 seconds to get the thing primed before...yup: brown, rusty disintegration. After I prime it, I will spend about six hours walking 'round and 'round my poor beast before I sigh, shake my head and get back with the program.
At any rate, what we have in my case is, in military terms, a retrograde movement. Sometimes we need to retreat in order to advance, see, and that's just what I've done. The time I would have spent in this piece rhapsodizing on the joys of welding will now be consumed in a discussion of the joys of bodywork. After all, there is no better time to attend to the minor dents and dings caused by an end-over-end flip or a paint-stripping place. I have every panel that can be exposed in full view, with no distractions like a drivetrain or interior or trim or electrical geegaws to obstruct my whamming the hell out of aforementioned panels. So let's go to work.
The first rule of straightening that precious sheetmetal is to have patience. Never use one blow of the body hammer when ten will do, or a hundred, or a thousand. Because, you see, if you use too much force, you'll do the exact opposite of what you're trying to do and stretch the metal in the opposite direction.
The second rule of bodyworking is that, as far as tools go, there are no rules. Use whatever gets at the blemish with the right shape to nudge it back into place. I have been known to use a wood-splitting wedge with the edge dulled to get into a tight corner. Be creative. Pieces of wood sanded into the correct shape, tire irons, hammer handles, pry bars, they're all fine implements in the right situation. There are even certain rare instances when a body hammer and dolly can do some good.
I started on the coupe at the front valence. I don't know how the idiots managed those dents, but they're dandies, and a great place to develop my bodywork chops. Why a great place? Because the valence will be hidden behind a spoiler, Einstein. I suppose you'd rather start with that blemish in the center of the hood. You'd best get a little practice first, because this stuff can be tricky. What I've done with the valence is pretty straightforward. First read the reference book on hammer-and-dolly technique. Then start from behind the valence and use a combination of hammer-on and hammer-off technique (I told you, read the book) on as much of the dent as you can reach. This won't touch the really hard-to-reach part in front at the very top. For that, I'm going to do something different.
To get the untouchable dents, I have a couple of methods at my disposal. They both involve the use of a slide hammer, with one being much less intrusive than the other. I'll go over the down-and-dirty method first. Get some sheetmetal screws. Take your Hole Hawg and drill a number of holes a size smaller than your screws along the exact impact area of the dent. It's usually the lowest part. Put one of the screws in the tip of the slide hammer, screw it into the first hole, and knock the sliding weight against the end of the hammer using minimum force. Don't try to take the dent out instantaneously or guess what: stretched sheetmetal. Continue along the line until the dent is nearly level with surrounding surfaces. This method will remove dents but leave you with a long series of very nasty holes. It is, in a few words, an ungraceful solution. I've pictured a slightly better method, even though it involves a bit of welding.
First, I'll construct an M1A1 dent-pulling machine. If it looks a lot like a pair of ratty channel locks with a nut welded onto the screw end, congratulations, Sherlock. That's what it is. In this case, it's a 7/16 x 20 SAE threaded nut, which handily fits the threads on the tip of the slide hammer. In this manner, once I've threaded the nut onto the slide hammer I'll have an implement with a gripping device at the end instead of a sheetmetal screw. In order to get something in place for the locking pliers to grip, I'll weld some 2.0-in. lengths of 1/16-in.-diameter welding wire into place along the dent, just where I would have drilled the holes in my former method. Lock the pliers onto the first piece of rod and gently use the slide hammer. Keep at it and the dent will gradually be pulled out.
Finish by grinding off the short lengths of welding rod and doing any minor hammer-and-dolly work to bring the former dent fully even with the surrounding surface. The disadvantage of this method is the use of heat, which will cause mild steel to rust like crazy, but I'm going to coat the former dent with a rust inhibitor, so I'm covered, literally and figuratively.
I know I'll have to repeat this process until my ears are ringing and my head is spinning, but I'll chill by chanting my mantra: "It's only a race car...it's only a race car...it's only...."
Also, we mustn't forget, in this, the year of the palindrome, that "race car" spelledbackwards is "disaster."