Fitting the old cowl

[mulwyk]

Yesterday I tried fitting the old cowl. The top cowl doors fit pretty good, and the nose bowl is OK. The problem is the bottom cowl where it fits to the nose bowl. The Dzus fasteners latch ok, but the cowl edge where it meets the nose bowl is all lumpy and wavey. See the photos.

How can I fix this?

The material is quite soft, I can bend it easily with my hands. My first thought was to make a wood form in the shape of the nose bowl and then hammer the cowl down around the form...but I'm afraid that would make the Dzus fasteners NOT fit.

What to do? I'm stumped.

[NY86]

Re: Fitting the old cowl

What to do?

Attach the part to the form using the holes for the Dzus fasteners so it doesn't change shape there, then hammer away!

[Hank Jarrett]

Re: Fitting the old cowl

Don't hammer! TAP!! You can "shrink" the aluminum by tapping the high spots with a bucking bar behind it. Think of the aluminum like it is clay. If you smack it, it will get thinner and wider. If you take a thick flat piece of clay and "ruffle" it up like your cowl edge, you can tap it down and it will flow out flat and get a little thicker. The key is DON'T HIT IT, just lots of gentle taps while you restrain it from spreading out or getting thinner. Takes some practice, but a good "old timer" body shop man can do miracles. He will be able to tap that wave out right in front of you (aluminum is actually FUN to do this with compared to steel cars). When you get good you can even do it without damaging the paint (yours is pretty wavy so you will need to do some repainting).
Watch out for overworking the aluminum. You may need to "soot" the metal and anneal it so it doesn't crack. Just go slow and maybe practice on a piece of scrap metal first.
Hank

[VictorBravo]

Re: Fitting the old cowl

Hank had the best idea if you're skittish, go to an olde-tyme body shop, or an ALUMINUM body hot-rod or custom car shop. Find the guy who builds aluminum body stuff... he'll be the guy who can also use an "English Wheel" tool. $20 or $50 might leave your hands for a half hour of his time, but you will get it back correctly the first time without damaging expensive parts.

There's an old tool called a "shrinking hammer" that was supposed to do this kind of job too. But, there is a widely available device called a "stretcher-shrinker" that will definitely do the job well.

If you are the do-it-yourself type, I think that finding someone with the stretcher-shrinker tool and borrowing it for an hour is the way to go. Start with a scrap of same thickness aluminum and see how the shrinker works (it's fairly simple actually). The shrinker will leave a rough surface on the metal, which you sand and polish off once it fits right. a Harbor Freight shrinker will work just fine on this type of soft aluminum.

[Mark Julicher]

Re: Fitting the old cowl

[QUOTE=Hank Jarrett;56798]Don't hammer! TAP!! You can "shrink" the aluminum by tapping the high spots with a bucking bar behind it.

Yes! and a slapper is much better than a body hammer for this task and a lead dolly or a shot bag is better than a bucking bar. Take your time. Practice on something else.

[Edwin Otha]

Re: Fitting the old cowl

I would run a shrinker down that edge. The more you hit it the bigger it will get. If you don't have acess to the shrinker you can use the body hammer with the waffle face and a pliable back-up dolly.
EO

[Hank Jarrett]

Re: Fitting the old cowl

This job needs the slapping paddle, not the shrinker. A shrinker puts lots of little waved in the metal and a shrinking hammer pulls the edges in by deforming the metal out of plane in two directions. What you want is to make the metal THICKER by pushing the extra metal down and not letting it spread out. It' kind of hard to describe, but picture clay in a pan where the clay is too thin and bigger than the pan. You "dome" the clay up and when you push it down slowly while not letting it spread out beyond the pan dimension it has to get thicker.
Check out some sites on "metal bumping". Shrinkers and waffle hammers are faster, but don't produce "pretty" results. Hitting to hard will always stretch the metal, tapping (when done right) will make it pull in and get thicker.
Hank

[Edwin Otha]

Re: Fitting the old cowl

I still vote on the shrinker. Sand the edge after you lose the excess. Slapping out a dent is tough on an edge. Mid-panel is a lot easier.
EO

[NY86]

Re: Fitting the old cowl

...hammer away!

Don't hammer! TAP!!

I meant "hammer" figuratively... :embarrassed

[Laz]

Re: Fitting the old cowl

I watched my friend build the lower cowl by hand from scratch. It was the Red Pre-war that won a lindy last year. He used a shrinker in this area. The trick is to do a lot of small shrinks. Hank is correct if you bear down on the shrinker a lot you will get a wavy pattern. Harbor frieght sells a shrinker that will work fine with this soft alluminum. When you get the rough shape you need use a flat slapper and a dolly. Very lite taps. take your time. This area will really not take that much work. Hope this helps.

[N96337]

Re: Fitting the old cowl

On a shrinker, if you use a chunk of emry cloth on each side of the metal, between the shrinker jaw and the metal, and use light pressure, you can shrink just fine without making any "tracks". It can be done by "tuck shrinking" with a hammer, but it's a slow process, and results can vary, depending on experience and patience. Metal only stretches when struck, even when "shrinking" with a hammer, and that's a tough concept to wrap your thoughts around at first.
JH