How to tackle a rusty rear wheel arch?

[Roadsport]

Would love some insight from more experienced metal workers. If I could for once avoid the trial and error scene.


If it can still be salvaged it (or some of it) should I fill it up with led or replace the panel in any case?
Is the led still the best option?
I´m afraiid the weld seam will start to rust in no time anyway. So is there a way to buy me even a few rust free years? Maybe apply gallons of waxoyl to inner wheel archers and hope that would seal and protect the welds? Maybe use body glue like they do on bodyshops with bigger body panels to prevenr heat expansions and pulls.

The case: Puma rear wheel arch




Thanks for your comments!!

-Markus

[Graham]

cut out butt weld new metal in and drown with waxoyl from the inside

[Roadsport]

Thanks Graham. Sounds simple enough. And I'll take your word for it. I believe that is the way to get it sorted. For a while anyway.

[exboyracer]

What Graham said

Beware though, the pumas (along with most modern cars) have very thin steel and welding a rear arch without causing distortion takes a lot of skill and patience.

[Pushrod King]

I'd start by grinding it back to find the true extent of the rust then trim the replacement panel so that there's about 50mm excess all the way around,then remove just the damaged part of wheel arch lip from the car,(ideally using an air saw but a thin cutting disc or even electric jigsaw will do),
trim the new arch lip so that it fits into where you've removed the old one then clamp the new panel to the car,cut through both the new and old panels with an air or jig saw 50 mm at a time tap the new panel (hammer and dolly)so that it's flush with the original panel and tack (stitch) weld about 25mm,starting from the bottom (leave the other 25mm for the saw blade) then continue doing this until the new panel is cut and welded all of the way round taking care not to concentrate too much heat in one place,then fill in the unwelded sections a litle bit at a time starting from the top then bottom either side so that there's less chance of distortion when it's cooled down grind the welds back a bit at a time,skim with filler and prep for paint etc......brush the inner welded part with primer then seam sealer before waxoiling.

[Roadsport]

Thats is a propper walk trough instuction. Thank you ! A very neat and clever idea to get a a nice flush fitting repair panel ! So after clamping the new panel in place I'll need to cut cut trough both panels. The new and the old. And tack it as I go?

Is it better to eventually fully weld the seam or should I tack it and fill with led? I was thinking of exploiting my father expertise. I'm a total waste of skin when it comes to led work but hes handy with it. This would leave less burnt, corrosion sensitive metal inside the wheel arch.

I hope I can somehow reach the inner weld seam with something to aply primer and seam sealer. Otherwise I have to spray around with waxoyl.

[Pushrod King]

Fill the full cut with weld by spotting an inch (25mm) at a time.

[Roadsport]

ok will do thanks again for the advice ! I really apreciate it!

This method leaves a gap between the repair panel and the original arch that equals the thickness of the pneumatic hacksaw blade right? Would a zero gap be more rust resistant?

[Pushrod King]

ok will do thanks again for the advice ! I really apreciate it!

This method leaves a gap between the repair panel and the original arch that equals the thickness of the pneumatic hacksaw blade right? Would a zero gap be more rust resistant?

The gap will be filled with weld

[Roadsport]

Right. Just need to pay close attention to sealing the inner weld then.

[Roadsport]

What Graham said

Beware though, the pumas (along with most modern cars) have very thin steel and welding a rear arch without causing distortion takes a lot of skill and patience.

Thanks for the heads up. I'll be sure to take my time.

[Pushrod King]

That's why you weld a little at a time and then grind a little at a time.

[Roadsport]

Figured that was the reason. I take it the one inch weld is short enough to avoid distortion even with these wimpy panels.

[Graham]

no you basically weld using a pulse method, i.e holding the welding torch without moving it you weld a single small spot by just triggering for a fraction of a second move the torch along a fraction and once the first weld has cooled to a dull red or even darker trigger another spot weld and so on, picture a nice bit of tig welding and your get the idea, if you try to produce a line of weld at any length your far more likely to either blow holes or warp things, if you can pack the panel above and around where your working with wet towels to soak up the heat your further reduce the chance of warping

[Roadsport]

After talking to our body shop guy he got me convinced than glue would be a good way to do this.
I've decided to give it a go and see how it'll come out.

Now, as long as I'm bonding the panel in place instead of welding I could use alloy repair panel. But would that be wise after all? Will the alloy and sheet metal make a reaction and corrote the alloy arch even faster than regular sheet metal?

[exboyracer]

Yes, where the alloy is joined to steel you'll get electrolytic corrosion. You might be able to sop this if you have a non-conductive adhesive, but over all it'd be much easier just to use a steel arch repair panel.

[Roadsport]

You may well be right. And the bonding not welding has some advatages compared to weldig so ... maybe I'll be able to fend of the rust....for the rest of the week anyway...