How to approach this rear arch replacement

[Cosantoir]

Hey guys,
I'm getting close to biting the bullet and starting the rear arch repairs on my FTO restoration project.

Over the past year, I've seen regularly mentioned "do not remove more material than you need to" when talking about body panels. So I'm looking to anyone who may have some experience here to share their experience or give me some advice on how to approach this repair.


So to start off here's what I have.
The bumper bracket at the swage line has completely corroded and along the arch, it's badly corroded.
The inner arch is corroded in a number of locations

You may notice that there are two bends just above the arch that may resist warping (maybe they won't) just below the large flowing line about halfway up the body.








This is what I have to replace I had a donor car and I cut out the inner and outer arch however the inner arch was in poor condidion.



Once the inner arch was removed the outer skin seems to be in good condition.

It's hard to tell here but this is the inside view of the outer arch




How would you approach this repair?

 

[Dcal]

Below is a link to what I did.
I didn't have a good second hand wheel arch to use so had to make bits from scratch.
I'm of the cut out as little as possible school, however if I had a source of second hand (or new) parts, I might change my mind.

25 year old Alfa 75 back from the brink (hopefully)

My mate made about 5 or 6 small different radius wheels for my dad for about 20-30 quid each. I think he has the dimensions and radius's to hand. He did have to fit bearings in them in the end though as they wouldn't turn when under tension. You'd still need the big flat wheel but I don't see...

www.mig-welding.co.uk

 

[Dell]

Hopefully you will have a jogger tool because that is the best way to go about it because the joggle tool will put a slight step in the panel you are fitting it will help stop distortion when welding, but still weld in small steps.
pictures of R/R I am doing

 

[tom2207]

start point is to clean everything up , and then look at what you have , and what you dont have .
I use scotch pads on a dynabrade for this , it will strip off paint and rust but hardly touch whats sound.
I try to avoid joggling in wheel arches as the double skin just creates a rust trap for the future . On a repair like that you have to get a good silver edge all the way round , you cant repair anything if you dont have an edge to work to , or from.

 

[Cosantoir]

Below is a link to what I did.

Like your post my fear is trying to get the inner and outer arches to line up properly as there is a constant 90° bend on the lip along the curve of the arch so will be a nightmare to try and replicate by hand.

Hopefully you will have a jogger tool.

One side of me agrees that this would make fitment much easier for the outer skin but seeing how bad the car got with moisture getting into seams it's constantly put me off. Do you make sure you use seam sealer on the back or do you find it's okay as is?

I use scotch pads on a dynabrade for this

Is a dynabrade like an orbital sander or one of those paint strippping rubber wheels? I've been using those sacrificial paint strippping wheels on the grinder and seem to do a great job

 

[tom2207]

sorry , 3 inch die grinder roloc type pads , there are lots of generic ones available at humble money , providing you have a compressor , if you dont have one ,a compressor is worth its weight in gold on the sort of project your at ,

 

[daedalusminos]

As @tom2207 says, you need to detrmine extent of the rust and your cut line - coating in that grey paint has just made the job more difficult.

I'm assuming you don't have the tools or time to fabricate an accurate inner wheel arch, it's probably got compound curves which would require beating and wheeling. More likely you'll have to fabricate from flat sheet sections, the technique will depend on the actual shape but it could be strips running circumferentially or radially or a combination of the two.

Use the old inner wing and outer as guides, cardboard patterns will help get the shape of the patches. You can get the inner to fit well to the outer as you build it on the bench but make sure the outer is not twisted when doing this - if there's a tendacy for the outer to loose shape off the car then get it fitting well on the car, clamp in place then weld a strengthening frame to it , un clamp and you'll have a strong outer to build the inner to.

The golden rule is to not weld the inner 'blindly', the outer needs to be fully clamped in place before welding the inner down the cut line.

 

[Nick DV]

Have a look at these, they may help

and

 

[tom2207]

as above , you can work round most things , the 90 degree lip at the arch is tricky , but instead of starting with a 10mm lip and trying to get it to fit , you can start with a 100mm lip and tack it where it does fit , then cut it back on both sides and weld the edge and dress back to a radius ,,, not ideal but very doable with patience , depending how good your welding is ,, one thing for sure , it will be better when your finished than it is now ,,, oh and a must have is a copper backer , or two ,,, I use a lump of copper about 75mm x 100mm x12mm for a lot of things , holes , plug welds , sharp corner backing , and just as a heat sink ,,, a lump of buss bar will get you by the very best.

 

[Nick DV]

sorry , 3 inch die grinder roloc type pads , there are lots of generic ones available at humble money , providing you have a compressor , if you dont have one ,a compressor is worth its weight in gold on the sort of project your at ,

As Tom says, all of this stuff can be picked up cheap enough from the usual places. I also use the hook and loop stuff, and in 2" for the hard to get to places.

 

[droopsnoot]

I've been doing a similar job on my project car, which also has a lip on the edge of the wheelarch. After cutting back the inner arch to good metal I clamp the replacement outer panel in place, then make a short section (maybe 6" at a time) of the inner arch edge, clamp it to the lip of the outer and trim until it's a good fit, then reach up and put a couple of tacks to hold it in place to the rest of the inner arch. Then I remove the outer arch, weld the inner in place from the "outside" which will then be hidden once the outer arch is done. The actual length of the section sometimes depends on how complex a shape it is - if it's a sharp curve, I might do two shorter sections. Once you have a couple of inner sections in place, it gets easier to clamp the outer in place as you have more to fix it to.

I'd agree about the joggling of the outer edge - you're making a future rust trap, and it'll be quite difficult to joggle an edge on a curved section because the "lower" part of the step will need to be shrunk because it'll need to end up at a smaller radius. The only way around that is to cut notches in it.

I'd also agree about only cutting out what you need to, but consider whether cutting a little bit more of the outer will allow you much better access to repair the inner. Also consider how you're going to dress the welds afterwards, make sure you weld in a place where you'll have good access.

 

[Cosantoir]

sorry , 3 inch die grinder roloc type pads. AHH yea that's what I'm using on the grinder.

AHH yea that's the heads I've been using. I have a compressor but haven't amassed too many tools for it yet. I've an orbital sander and I've been using it mainly for spraying.

I'd like to have gotten a nibbler earlier on in the project and I'm wondering do I need a grinder along with the dual action? Would be nice to have a neat a tidy cutting disk and again something to get into corners with

As @tom2207 says, you need to detrmine extent of the rust and your cut line - coating in that grey paint has just made the job more difficult.

The golden rule is to not weld the inner 'blindly', the outer needs to be fully clamped in place before welding the inner down the cut line.

That's just rust converter after I removed the inner

as above , you can work round most things , the 90 degree lip at the arch is tricky , but instead of starting with a 10mm lip and trying to get it to fit , you can start with a 100mm lip and tack it where it adoes fit , then cut it back on both sides and weld the edge and dress back to a radius ,,, not ideal but very doable with patience , depending how good your welding

Good shout on oversizing the lip and trimming it down later

After cutting back the inner arch to good metal I clamp the replacement outer panel in place, then make a short section (maybe 6" at a time)

This is a very good shout I was all in my head about making this out of a single piece and if it went wrong how much material I'd waste. Smaller sections are way easier.

Then I remove the outer arch, weld the inner in place from the "outside" which will then be hidden once the outer arch is done.

When you were tidying up everything did you use seam sealer then or something like epoxy mastic? On the wheel side to finish?
With that said I know I'm going to replace the outer skin but I wonder if I'm better

I'd also agree about only cutting out what you need to, but consider whether cutting a little bit more of the outer will allow you much better access to repair the inner. Also consider how you're going to dress the welds afterwards, make sure you weld in a place where you'll have good access.

So I know I'm gonna replace some of the outer skin how much... Rust will decide!

But for the inner arch I wonder if I'm best to cut out the outer skin where I can then have a look at the inner arch from the top and see the rust and just cut out sections of the inner arch that are needed instead of the entire thing....

In fact I wonder if the arc is the same the whole way around the arch? I could probably get away with using some good patch pieces from the donor arches and save myself a headache?

 

[Cosantoir]

Have a look at these, they may help

and

You know what I've seen that crusty video so many times pop up and skipped it will watch it now

 

[Burdekin]

That inner looks really crusty. You need to get in and clean it up and see what you are dealing with. Also you might get a cheap inner arch repair panel, maybe not the same model if not available but there will be one that is close enough that you could make fit.

Check out Fitzy's YouTube channel to give you some ideas how to repair and minimise distortion if mig welding it.

 

[Nick DV]

You know what I've seen that crusty video so many times pop up and skipped it will watch it now

I know I keep on about Fitzee’s stuff, but it’s really helpful and no bull***t about having to spend a fortune on fancy tools

 

[tom2207]

you dont actually NEED a nibbler , but you wont get far without a grinder , ideally two . one with a flap in it and one with a slitting disc in it , it will save so much time.

 

[tom2207]

I know I keep on about Fitzee’s stuff, but it’s really helpful and no bull***t about having to spend a fortune on fancy tools

Or spend twenty hours putting a patch on either. Some guys work on things that are worth quarter of a million and twenty hours to fix a wing is nothing , I work on stuff driven by farmers and twenty mins to fix a wing is frowned on ,,, time costs , and you have to set a value on the job before you start , even if its for yourself , are you willing to invest the time into the end result.

 

[Dell]

Cosantoir
always without exception cold galvanise, lots of brushable sealer if you can get to it if not then loads of wax oil
Dell
PS
although I worked on vintage cars most of my working life I don’t any more, the Rolls Royce I am doing at the moment belongs to the owner of the coach company that I run the bodyshop for, and he asked me if I could paint it but as things do turned out to be a lot more ( rotten as a carrot ),I don’t do much fabricating now because I am 70 and have gout in both hands But I still make panels for the coaches and buses.

 

[Cosantoir]

AHH to be fair Fitzey is the man!!

So having watched his video he said that usually the outer arch is worse condition than the inner arch.

So thinking open up the outer arch and inspect the inner cutting out the bad bits, patch the inner arch and line it up with the existing material for the inner arch and cross check it with the replacement outer arch. Then weld in the outer arch before plug welding the inner arch in place.

Saying this out loud I think Clecos or Skin pins are going to be needed for this job.

@Dell what's the difference between your everyday zinc spray and galvanize spray?

 

[Nick DV]

Or spend twenty hours putting a patch on either. Some guys work on things that are worth quarter of a million and twenty hours to fix a wing is nothing , I work on stuff driven by farmers and twenty mins to fix a wing is frowned on ,,, time costs , and you have to set a value on the job before you start , even if its for yourself , are you willing to invest the time into the end result.

Not quite sure what you are saying here! Are you saying that Fitzee’s stuff takes too long?