Welding sill bottom

[jb2000]

Most car sills comprise a box section formed by two C sections arranged to face one another with a projecting lip top & bottom which is spot welded.

Q - I have often wondered if replacing a small section or the entire bottom can you just seam weld a plate across, with plug welded double L-angle to replicate the lip?

A simple plate would not be as stiff, unless of substantially increased thickness .

Thanks.

 

[the snooper]

how ever you fabricate the sill is upto you as long as it does the same job BUT you can only plugweld a full panel as original, any patch repair must be fully welded so if you make up your own sill the actuall pannel must be fully welded then you could plug weld it onto the car as the original was

 

[Engineer]

Easy way to repair holes in sills, is to fold up a 90 degree edge on a 1.2mm patch large enough to overlap the holed area by about 30mm, plug weld the 90 degree edge to the existing lower sill return, then push the patch up against the sill, and seam weld the rest continuously. Have done an awful lot of repairs in that way in the past, and as long as the lower return is still intact, the finished job looks quite neat, and is fast and easy to do.

 

[jb2000]

Noted all, basically the sill has a factory plastic side skirt which locates into square holes which have a rubber seal on them. The seal is hilariously ineffective so there is a bit of orange edge-in corrosion in some places.

The sills look like new inside from a good nose around, however that means nothing until a full endoscope survey is done. The lips are vulnerable from cracked undercoating so there is always something to "catch early".

If a lip has gone both sides it is just a matter of recreating a relatively simple shape, the steel is a bit thicker but that just makes welding a little easier.

 

[gavuk]

Easy way to repair holes in sills, is to fold up a 90 degree edge on a 1.2mm patch large enough to overlap the holed area by about 30mm, plug weld the 90 degree edge to the existing lower sill return, then push the patch up against the sill, and seam weld the rest continuously. Have done an awful lot of repairs in that way in the past, and as long as the lower return is still intact, the finished job looks quite neat, and is fast and easy to do.

I used to do exactly the same ,nowdays I seam weld the lower sill return,rather than just leave on the plug weld...As Snooper says ,you can only plug weld a complete new panel,ALL patches must be fully seam welded,at least thats the way I understand it ?...and the way the forum has interpreted the mot manual...

 

[Engineer]

Might be worth having a good read of the MOT tester manual, as there is no need to fully seam weld repair sections in areas where the original panel was spot welded. I went into this with this with the local DOT testing station, whose inspectors check standards at garages doing MOTs, and they confirmed that its perfectly ok to use spot or plug welds, where used originally, but obviously patch repairs have to be fully welded.

 

[Wozzaaah]

^That is exactly as described in the tester's manual, however, one thing to bear in mind (which is in the same section of the manual) is that to satisfy that criteria ALL of the piece you're repairing must be removed.
e.g. When patching a sill, the rot needs to be cut out and the sill lip removed so you're plug-welding to the inner sill, not the remnants of the rusty outer one.

 

[malcolm]

Can't make head of tail of the descriptions in the thread without pictures, but whatever the actual rules I'll tend to completely cut out rusted areas, seam (butt) weld where there was originally no panel join and plug weld when there were originally spot welds.

Something like this: http://www.renault4.co.uk/r5-rear-suspension-repair.htm

 

[schnappi]

I do my sill repairs the same as Engineer, Wozzaaah and malcolm suggest and have never had a problem with the MOT man.

 

[Wozzaaah]

Can't make head of tail of the descriptions in the thread without pictures, but whatever the actual rules I'll tend to completely cut out rusted areas, seam (butt) weld where there was originally no panel join and plug weld when there were originally spot welds.

That is correct, as per the manual but this should help clarify what I said in my previous post.

 

[gavuk]

I went into this with this with the local DOT testing station, whose inspectors check standards at garages doing MOTs, and they confirmed that its perfectly ok to use spot or plug welds, where used originally, but obviously patch repairs have to be fully welded.

Fair enough ,i will revise my definition of a patch ......i've been thinking anything other than a full sill is classed as a patch ....so whilst using plugs to position ,i've also seam welded the bottom edge...I've had no problems with mot tests either...

 

[malcolm]

Definitely agreed Woz. Plug welding is not for patched over repairs. I hate people adding patches over stuff as the resulting double skin causes so much rot. I remove them and do the job properly when I have a car to restore.

 

[Engineer]

In general years back when there were still quite a lot of rusty old bangers on the road needing MOT welding pretty much every year, owners didnt want to pay to have full sills fitted, so patching up holes in the way outlined in an earlier post of mine, was very common.

For most people restoring a collectable car today, if they are doing the work themselves cost is not an issue in many cases, so welding on complete sills in the same way the factory would have done is quite feasible. This is obviously a far better way to do the job, than patching or bodging on thin cover sills.

 

[rikrobson]

The manufacturers spot weld because its quick and cheap for them to do on a production line and now with robots. If you've got the time you may as well seam weld the joint as it will be stronger and stop moisture getting in between the two panels.