Need new door sills welded - what problems can I expect?

Only by dodgy, back-street bodgers.

The rot hasn't been cut out, so it will come back through the new panels as well as spreading into the floorpan.

Find someone else to do it - the only proper way to replace sills is to cut the old ones out (or the rotten parts of them at least) and replace with new metal.

Well, I'm assuming he will cut out the rusty parts - he always has in the past.

But given that the entirety of the old sills isn't removed, will the door positions need to be adjusted to accommodate the extra thickness?

no. there is plenty of room for an oversill.

mrcheerful

It depends on the sills. OEM panels will need the originals removed. Oversills are designed for doing as you say, and won't be a decent fit if you remove the old.

Oversills tend to be a very short term measure as you can't check what's behind the rotten one and fix that too where needed.

I saw a truly impressive bodge on a sill recently. Not only had someone simply tacked a cover sill on, but they'd only used the top half, welding it halfway down the original sill. The only explanation I can think of is they didn't want to weld underneath the car...

Needless to say, there's a fair smattering of rust along the whole thing.

These are definitely not OEM - it specifically says so on the labels.. They're from a company called Hadrian, who seem to supply many of the panel shops. I can post details if anyone's interested.

As I said, hopefully the rotten parts will be cut out before the new sills are welded in.

What I don't understand, though, is why any residual rust in the old sills will affect the new sills. Aren't they all galvanised these days?

no, just an anti oxide coat if you are lucky, galvanising is usually applied to a completed structure. probably though by the time the rust comes back the car will have gone to that breakers in the sky

mrcheerful

Well that bodge is better than welding the cover sill to the floorpan (only) as it retains the original joining points for the sill construction. With an oversill if the inner sill rusts along the bottom edge you won't know and the strength is compromised. I suspect that it wasn't an oversill at all but a regular one that wouldn't fit over the old properly so it was cut. Can't imagine a sill rusting from the top down though.

Loads do, usually from the outside in. Stonechips get caught between door and sill, people drag legs, boots, heels, dogs and stuff over the paint, it's rarely washed/polished properly.

An unmodified/treated early RX8 would probably - eventually - rust from the B-pillar catches down, as the early seals on the door used a rigid fixing that trapped and rubbed grit into the paint, causing little spots of rust to appear. The fix is to clean area back, repaint and fit a strip of 3M film, and later cars are not affected apparently (mine is getting 3M film regardless, but I also clean and wax the sills every week or so).

Richard

The message from snipped-for-privacy@yahoo.co.uk contains these words:

You've not had a Maestro then?

Thought they went all over at once?

The message from "PC Paul" contains these words:

No, for a good fifteen minutes you could catch one rusting from the top of the sills where they met the middle pillar.

I am counting on this!

As regards the MOT, if there is corrosion in the sills, do they have to be replaced completely (even if this means a new sill over what's left of the old) or is it acceptable to simply patch the rotten bits?

Depends on where the rot is and how far it's spread.

When we had a couple of old Fords - a MkII Fester(ing heap of iron oxide) and a MkIV Scrote, both of 'em had been patched on the sills.

You can patch them provided they are seam welded - this proves there is sound metal where they are welded.

Thanks. The MOT guy did say something about continuous welds but he seemed to imply that only a complete sill would do.

What you want to acheive is to make the repair structurally sound. For passing the MoT however you need only make it look like it's structurally sound. There's no need to repalce the whole sill but sometimes it's easier to do that than cut out and patch lots of holes.

Ideally, yes, provided there's metal to weld to at the top of the sill(s). In my case, the tops of the sills seem to contain more filler than metal. These never seem to get checked at the MOT.

Anyway, it passed the MOT this morning.

See my second sentence above.