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  #1  
Old 10-25-2010, 04:45 PM
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Smoothing firewall

I would like to plate over the passenger side of my Nova firewall to eliminate the AC assembly (going Vintage Air) and provide a nice flat & smooth look under the hood. I have seen a few different methods for this and my preference is to do it with one piece of sheetmetal rather than closing off individual holes and using body filler. What I'm not sure about is whether or not cutting out the old material is necessary or if I can just plate over the top of it. Any opinions?

Here is an example where someone cut out some sections of the firewall before plating it:





Finished product of above with paint. I like how they relocated the wiper motor to under the driver's fender.



And here's an example where I think they just plated over the whole thing and welded the perimeter. I'm thinking if I went this route, I wonder if I should put some rosette/spot welds in a few places to keep the new metal from rattling against the old metal?



This is the same firewall as above after paint.



Any tips on best practices for doing this are greatly appreciated! I haven't done a whole lot of sheetmetal work yet, so I am open to ideas.
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Last edited by TheBandit; 10-25-2010 at 05:21 PM.
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  #2  
Old 10-25-2010, 04:55 PM
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I would cut out as much of the unnecessary sheetmetal as possible. Basically as shown in the second picture. Overlapped sheet metal is a breeding ground for rust....it'll come back and bite you. And yes to welding to support members in the center area wherever you can. Where you do have overlapping sheetmetal coat both pieces with weld thru primer. It comes in an aerosol can.....it's basically a cold galvanizing compound.

When welding autobody sheetmetal you want to make a series of tacks, and skip around so to not build up too much heat. I like to use .023 wire for welding autobody sheetmetal.
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Old 10-25-2010, 05:25 PM
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I would cut out as much of the unnecessary sheetmetal as possible. Basically as shown in the second picture. Overlapped sheet metal is a breeding ground for rust....it'll come back and bite you. And yes to welding to support members in the center area wherever you can. Where you do have overlapping sheetmetal coat both pieces with weld thru primer. It comes in an aerosol can.....it's basically a cold galvanizing compound.

When welding autobody sheetmetal you want to make a series of tacks, and skip around so to not build up too much heat. I like to use .023 wire for welding autobody sheetmetal.
I think Im gonna agree with the captain on cutting out the old stuff. If you dont have a set of clecos I would recommend picking some up, they would make a job like that much less of a headache since you can't really clamp around it anywhere. On second thought, if you plan on putting plug or rosette welds to the structure behind, make sure you pound the structure behind out to where it is touching your flat sheet.. It would suck to have an otherwise nice flat panel and have a bunch of puckers in it where the plug welds are.
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Old 10-25-2010, 07:45 PM
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Look hard before you cut, the complete firewall is structural. So make sure that you can maintain or increase the strength when you do whatever, unless you are going to cage it, then cut everything!
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Old 10-25-2010, 07:53 PM
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Originally Posted by entropy View Post
Look hard before you cut, the complete firewall is structural. So make sure that you can maintain or increase the strength when you do whatever, unless you are going to cage it, then cut everything!
This is why I am aprehensive about cutting large sections out of the firewall, not to mention I'd prefer to do this without tearing apart the interior if I can get away with it.
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Old 10-25-2010, 07:58 PM
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not to mention I'd prefer to do this without tearing apart the interior if I can get away with it.
Get into all of it. Access to what you cant see, fire prevention, dead mice and bad wiring...etc.
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Old 10-25-2010, 08:13 PM
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watch for fire if you leave the interior!!
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  #8  
Old 10-25-2010, 09:29 PM
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JaysinSpaceman JaysinSpaceman is offline
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E has a good point about being aware of the structure that you are potentially destroying. I have seen this done three ways and I think that two of them are wrong.

1. Just slap a piece of sheet over the whole thing and either weld the entire edge or simply tack the edges and fill with seem sealer. WRONG (at best this works to trap moisture and will rust out shortly, at worst it will fail at the welds or tacks and undo all the work you did.)

2. Cut out the firewall all the way around the edge, disregarding any strengthening structure behind it and then welding in one big flat piece of steel in it's place. WRONG (at best you just end up with bad cowl shake, at worst the first time you hit a bump the doors no longer open and close and the gap around the hood goes all out of wack with no end to rattles and oil canning of that new fire wall)

3. Carefully find all the structure behind the firewall and drill out all spot welds and carefully cut out the firewall at the edges (or drill out all the spot welds at the edges) and then replace the firewall with the flat (but beaded) replacement and weld through all the original spots. Making sure all the support structure you carefully removed get put back. RIGHT

#3 is the only right way I see to install a completely smooth firewall. Personally I have carefully made patch panels and welded up all the stock (and badly drilled) holes, carefully MIG or TIG welded the patches in and metal finished to the best of my ability. It looks better to me then the abnormally smooth replaced firewall. In fact I am doing just this on a 53 chevy truck cab for a customer right now.

There's my $.02
Jaysin
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  #9  
Old 10-25-2010, 11:43 PM
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I am no sheet metal expert but I agree with Jaysin. Carefully cut out the firewall making sure that you leave any support structure in place. I have done lots of sheetmetal repairs on airplanes and the things the engineers stress the most is to maintain any and all support structures.
If you were to just lay another sheet of metal over the current fire wall you would need to smooth the existing metal as much as possible and then make spot welds about every 1" to 2" and apply some kind of sealant between the 2 pieces to keep out moisture and corrosion.
My .02.
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  #10  
Old 10-26-2010, 12:58 PM
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Sometimes I ask questions and make statements well before thinking things through. I'm not sure why I had it in my head that I would start cutting and welding on the firewall with a complete array of kindling (insulation, wiring, plastic) on the oppossite side. Thank you for all the intelligent responses and good advice.

There are definitely structural elements to be concerned about, which is partially why I like the idea of plating over the existing firewall. I understand the concern for trapping moisture, but I was hopeful a decent weld along the perimeter and seam sealer would be enough to prevent that.
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Old 10-26-2010, 01:18 PM
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JaysinSpaceman JaysinSpaceman is offline
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Clint,

The problem with the plate over idea is that regardless of how well it is done there is really no way to keep out condensation and there will always be water/rust issues. I've done enough rust repair on various vehicles to know that anywhere there are two pieces of sheetmetal the are against each other there will be rust even in places that shouldn't be able to get any direct water contact. I really think that doubling up layers on the firewall is just asking for problems. And there is no way I would try this job without removing the interior materials, that is just asking for fire.

Jaysin
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  #12  
Old 10-26-2010, 01:41 PM
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I smell what you're steppin' in.

Sorry I am very sleep deprived lately with the newborn and my IQ has dropped to near-drooling levels. I'm unable to think clearly. I am rambling. I am typing things like "I smell what you're steppin' in". I am talking about welding with interior in place. Perhaps I should just dump a few gas cans out and light a match while I'm at it.

Please ignore me. I may have to delete this thread and start over when my brain cells return.
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  #13  
Old 10-26-2010, 02:37 PM
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...when my brain cells return.
friend... newborn, braincells return... You got years, so don't hold your breath, just soak up all the new experiences because nothing will ever return to what was, you will adjust to what is
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Old 10-26-2010, 03:46 PM
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I had a bad feeling you'd say that. Guess I better get used to the new zombie version of myself.
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Old 01-11-2011, 03:38 PM
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i cant remember pre-kids.
wait till you been away at work a few days, go out to workshop and cant find that half inch rd tube you bought til you go in to say night to your 2x10 yr old girls and your 2yr old girl and find the elder ones have built themselves a stand for telly dvd and ps3.
at least my eldest two boys ask before they pinch stuff.
my 3 yr old boy just gets a hot chocolate and comes to watch and have a go.
oh and if you want to know about sleep look in dictionary.
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  #16  
Old 01-11-2011, 06:54 PM
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You make some excellent points and observations. I will have to look in the dictionary for this thing you call "sleep". I can't remember what that is. Fortunately I am starting to adjust to the baby while he adjusts to the world. He's sleeping more and so am I, but like you've all told me, things will never be the same! I am learning to live with my new mental handicaps.

As for the original topic, at this time I'm no longer planning to do any work to the firewall.
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  #17  
Old 01-11-2011, 08:55 PM
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hahaha ive noticed that as timegoes by with my kids my projects become les time consuming or i give myself a stupid amount of time to complete a project and just wait till your elbow deep in something and got your grove going thats when your gonna hear the yelling from inside the house saying daddy daddy look
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