Mot repair

[pptom]

I'd appreciate some advice please. This will be my first welding job on the car and was wondering about how to go about arranging the patches.
Its in the rear wheel arch, the pic below shows the rust patch just above the rear axle:

This next pic gives a bit more detail, you can see that essentially there are two different panels that have rusted, the outer one is simply body skin, very thin and easy to patch, but the inner one is more chassis related, about 1mm thick, maybe a little bit more.

To gain access to the inside face would involve removing the rear axle, so i'd want to avoid that if possible. I was thinking along the lines of seam welding a square plate over the chassis item, and then covering this with another plate, again seam welded, over the bodywork, all welding to take place on the outside, as facing the camera.
When i had a breif chat with the Mot chap, he just said that it needs a small patch in the arch, I couldn't see the area at the time because it was hidden behind the wheel, so didn't question him further.

 

[Chickenjohn]

You need to cut all the rust away before making up your repair section to weld in. Its hard enough welding underneath a car, on your back without having thin metal blowing away as you're trying to weld to it. I would cut the outer skin back (tin snips are more accurate) till you get to sound rust free metal on the inner skin. Then cut out all the rust from the inner skin- make it a regular shape like a triangle or square, this will make making the accurate repair patches easier.

Then seam weld the inner one in, paint both sides with Zinc weld thru primer (galve spray) then seam weld the top piece in.

is the car a valuable (to you) emerging classic that you want to repair as original? or is it just an old banger- bodge it through the MOT job??? If the latter, you could replace both skins in the rusty area with a big 2mm thick patch that will replace the two ~1mm skins. If you cut the outer skin hole slightly bigger than the inner then you could zig-zag your weld and weld the 2mm plate to both skins. Seam weld the inner to the 2mm plate (plate flush with the rear) then bridge the small gap between the outer skin and the front of the plate. This is butt welding BTW, if lap welding you will have to drop the axle to gain access from the other side.

It looks like a poor design on the car, a rust trap if I ever saw one.

 

[malcolm]

What does the area do - wondering why the area is reinforced - seat belt mounting or something? Are there any crossmembers or floor panels attached to the rusty area? Also how far around the hole does the reinforcement go?

I've been known to replace double skinned areas with single skins, but it does depend on why the area was double skinned in the first place.

 

[Chickenjohn]

Malcolm - "but it does depend on why the area was double skinned in the first place."

Possibly for ease of manufacture?? Thin double skins can be easily spotwelded by robots at the factory.

 

[Justme]

You could sepperate the two skins & use a thicker single new plate between the two skins. Weld to the inner skin using pre drilled holes to spot (looks like the original was spotted so should be ok) to that plate & seam to the outer skin. Does look like you could mig the inner skin from under the car too.

Oh & it looks like 3 or more skins to me from the pics.


Justme

 

[malcolm]

Possibly for ease of manufacture?? Thin double skins can be easily spotwelded by robots at the factory.

OK - probably the area is double skinned to save making the whole panel twice as thick. I was thinking difference between seatbelt mountings (where you would more likely do something involving an overlap so some welds are in shear), or something that is just that way to make it easy to make which could be happily redesigned.

 

[pptom]

A couple more pics, The first one is from the inside looking out, you can see the rear axle at the bottom of the pic, locating onto the box section crossmember on the right hand side

The rust area seems to be the main load bearing structure going forwards, there are chassis rails going backwards, towards the rear of the car, but going forwards its just these side pieces and the boot floor skin (top of pic)

This next pic is taken from the rear of the car, looking forwards. The axle fixing from the previous pic is 1/3 up the pic on the left hand side. You can just make out the silver of the repair area, just in front of the rectangular bump stop, in front of the axle carrying box section. And there are 3 skins!

 

[fingers99]

What is the car?

I really don't think you're going to be able to do that without removing the axle.

 

[pptom]

http://www.rallyeregister.co.uk/s1intro.htm

 

[malcolm]

The crossmember doesn't look too bad. I bet the double skin is in there for the bumpstop. I'd go with what Chickenjohn said. Cut all the rotten metal out from the wheelarch side, clean up the ends of the crossmember, then plug weld whatever you weld back onto that. I can't see much advantage of welding from behind.

 

[fingers99]

I'd think that's worth keeping and doing up well. Are any replacement panels available (given that they'll all rot in the same places).

 

[Splatfest]

If you are intending keeping the car taking the axle out would be a "stitch in time saves nine" type job.Having the axle out of the way would let you poke about to see what the rest is like.It would be a sickener having to get under there again the following year when another spot rears its ugly face. It would also let you get comfortable to weld up the repair patch.Theres nothing worse than standing on your head to get that last 2" of weld on because its in an awkward place.

 

[jaykay]

hi pptom i see your n/hampton.get over to ave.panels at rushden they do most repair parts for most cars.
what car is it???
also on mot it says about rust with in 12" of suspension mounts being a fail.