Advice on which way to weld my car's outer sill.

[MalcolmB]

Hi all. I am new to MIG welding but I've been practicing a lot on a scrap part of my car and other bits of metal. Thanks to this site and it's guides and the forums I've learned a lot.

I have my MOT in November and I have just noticed my outer sill is crumbling away. I have had this patch welded twice already over the years and it fails after a few years each time.
I'd like to fix it myself this time and hopefully do a better job of it. Obviously my welding won't be better than the pro but the prep and painting should be.

Here is the ugly sill in question:

I need to repair the arch bit too where it meets the sill on the left and on the right you can see a newer patch he put on when the join from the earlier patch to the original sill rusted through.
I intend to buy these instead of forming it out of sheet metal.

Question #1 I have is: do I cut off the amount of one of those new sills that I need to replace the stuff in that photo or do I keep it as one piece and replace the entire sill. That square patch makes me want to replace the whole thing so that doesn't happen again and also more holes might appear in the future. On the other hand there will be a lot more welding and it seems a shame to cut off perfectly good rust free sill.

Question #2 I have is: regardless of whether I replace the whole sill or just that back part what is the best way of joining it with the body of the car at the top? The replacement sills clearly have enough metal to go right up to where it was spot welded inside the car as shown in this photo with the green arrows.

So do I spot weld the new sills on there and then seam/stitch weld the other bits (the pillars and so on.) The problems I have with this is that it seems wasteful to remove all that perfectly sound and painted metal indicated by the red arrow. Also my shoddy attempts at welding would be visible to people and myself when going into and out of the car.

I was thinking instead that I could weld the sill on along here:

which is behind this rubber seal and just above the top curve of the sill but below those studs that hold the seal on. This would hide it behind that rubber. I worry though that this would involve a lot more welding and perhaps it wouldn't be as structurally sound doing it that way?

I have the other side to do at some point but that isn't MOT critical right now.


Any opinions or advice is appreciated. You might well say it's too big of a job for me to do but I am going to attempt it anyway. :-)

 

[BrokenBiker]

Basic rules of repairing cars...get the whole panel if possible, expect that panel not to fit at all and need modifying or panel beating to make it fit.

If the original was held on with spot welds, the new panel can be held with similarly spaced plug or spot welds.

If the old panel wast stitch or seam welded, the new panel should be. It was done like this for a reason.

Where ever you 'see' rust, is just the start, it will be worse than it looks under the paint which is usually why most repairs fail, they dont cut back far enough to proper good metal and then the rust gets around the new patch

Finally, if you dont know what you are doing, please practice first.

 

[Domdom]

Ok, not wanting to plug my own work, but take a look at post 89 and work your way from there.
Post in thread 'Sierra XR4i full restoration.'
https://www.mig-welding.co.uk/forum/threads/sierra-xr4i-full-restoration.111673/post-1889355

That is what you’re likely to find so be prepared for it. My advice is to get the car up on big stands, nice and high so you aren’t working uncomfortably. Take the door off. Then gently start cutting out the obviously rotten bits, not the entire sill. On the Sierra I only replaced the full sill on one side, the other side was done with bits let in where needed.

Welding - holes and plug on seams but stitch butt welds where you are joining a piece to the old sill. For the latter, check out YouTube Fitzee’s cut and butt method. It’s worth an hour watching some of his methods.

Boroscopes help as well. You want to see how much else is bad on the inside, even where the outside is OK. You might find the inner sill is bad as well. Just a cheapies thing off Amazon that connects to a phone. If the inner sill needs work as well it’s a different matter, hopefully it’s OK.

When you’ve done, get some rust preventer and spray it inside the sill. Lots of it. Dinitrol, Waxoyl, etc, there’s plenty of other brands too, many of which have been covered in this forum.

Good luck, and enjoy it. Very satisfying when you’ve done it.

 

[Seadog]

The patches in the photo were professionally done?

 

[Morris]

The patches in the photo were professionally done?

Nobody is saying what profession. Hairdresser is my best guess.

 

[Morris]

I strongly advise reading through the relevant MOT manual section before starting.

MOT inspection manual: cars and passenger vehicles - Appendix A: Structural integrity and corrosion - Guidance - GOV.UK

Assessing corrosion and methods of repair for car and passenger vehicle MOT tests.

www.gov.uk

 

[Misterg]

So do I spot weld the new sills on there and then seam/stitch weld the other bits (the pillars and so on.) The problems I have with this is that it seems wasteful to remove all that perfectly sound and painted metal indicated by the red arrow. Also my shoddy attempts at welding would be visible to people and myself when going into and out of the car.

I was thinking instead that I could weld the sill on along here

Just on that^

It's easier / faster to plug weld to the flange neatly than to seam weld anything neatly. You'll grind the plug welds flat(ish) and the results will be hidden under the door seal.

If there's any sound metal left, you could weld along the outside corner (right next to the existing weld line), but I somehow doubt that there will be. I would avoid welding near an internal corner like the plague as it is difficult/slow to clean it up afterwards.

Beware - it's not clear from the ebay listing whether they're actually replacement panels, or if they're 'cover sills' (intended to fit over the top of the old ones). If they're cover sills, they won't match up if you try and join them to the originals.

Good luck!

 

[Smallfry]

I wouldn't bother with patches if you can get replacement panels.

Be aware that non genuine panels or not always a great fit. Definitely fit the flanges under the door seals, BUT, don't cut anything until you have the new sills, and trial fit first. Yu will probably find that the ends where they are folded to fit the wheelarch are crinkly and look sh*t. Pie cuts, dressing, and rewelding are the cure.

Take photos of the existing sills all over, so you know how they were fitted. I normally forget after a couple of hours.

When you cut, don't try to cut back the body to the join where the new sill will be butt welded first time out, leave an inch or so, and keep trial fitting.

 

[MalcolmB]

Just on that^

It's easier / faster to plug weld to the flange neatly than to seam weld anything neatly. You'll grind the plug welds flat(ish) and the results will be hidden under the door seal.

If there's any sound metal left, you could weld along the outside corner (right next to the existing weld line), but I somehow doubt that there will be. I would avoid welding near an internal corner like the plague as it is difficult/slow to clean it up afterwards.

Beware - it's not clear from the ebay listing whether they're actually replacement panels, or if they're 'cover sills' (intended to fit over the top of the old ones). If they're cover sills, they won't match up if you try and join them to the originals.

Good luck!

There is another listing where similar panels are listed as replacement panels.
I agree with the plug welding but seam welding will still have to take place and they will be visible when you open the door.
The outside corner makes sense for ease of cleanup but I was thinking that would ruin the stock corner and be visible. I agree the internal corner would be harder to grind and clean up but it would be hidden. That was my thinking.

 

[MalcolmB]

For the latter, check out YouTube Fitzee’s cut and butt method. It’s worth an hour watching some of his methods.

I think I watched a few of his videos. I think he's a Canadian guy? The thing I wonder about that is surely there would be a gap between the original car metal and the new piece that is the thickness of the cutting disk?

 

[BrokenBiker]

The patches in the photo were professionally done?

that just means someone was paid for the work...doesnt mean it was worth the money

 

[BrokenBiker]

if you realllyyyyyy want to know how to weld a car up...there is this series thats worht a look...takes a few cups of tea to get through though

 

[Domdom]

I think I watched a few of his videos. I think he's a Canadian guy? The thing I wonder about that is surely there would be a gap between the original car metal and the new piece that is the thickness of the cutting disk?

He angles the cutting disc if you look carefully. That leaves a smaller gap, which you need if you want to avoid the oil can effect. Metal expands when heated by welding so you need a place for it to go or it can distort.

 

[MalcolmB]

He angles the cutting disc if you look carefully. That leaves a smaller gap, which you need if you want to avoid the oil can effect. Metal expands when heated by welding so you need a place for it to go or it can distort.

I think I noticed this with my practicing but also I noticed gaps caused blow through more. I'll give that a shot. Need a bit more practice cutting with the grinder.

 

[MalcolmB]

I am still unsure as to whether to just cut of what I need from the replacement panels or use the whole panels all the way along.

 

[Pigeon_Droppings2]

I am still unsure as to whether to just cut of what I need from the replacement panels or use the whole panels all the way along

Play it safe and make that decision when you have all the information about what you are dealing with.

For example...If you clean it up and cut it open and the rust is very localised then I'd probably just do a local repair. If the corrosion is everywhere then do the whole panel maybe.

.9mm/1mm slit disc gap is what I've always done for butt welds.