Mig welding car sills

  1. ade jiggly joggler!

    Posts: 7
    Hi guys,

    I have a Vauxhall Nova and will shortly be attempting to replace a whole complete sill section (passenger side).

    What I want to know is on the bottom line (the bit thats spot welded to the chassis) hows the best way to attach it?

    Puddle weld or 1 long continuous weld?

    I want it to be as neat as possible and have seen pics of a bloke welding a nova sill (passenger side) where he'd got a grinder and cut 25mm slits every 150mm along the length then welded along these.

    This soulds like the best way but how do I ensure the inside is sealed properly? Is it as simple as just running a bead of seam sealer along the bottom edge then waxoyling the inner cavity???

  2. peterd51

    peterd51 happy to be here!


    unless the MOT rules have changed again then it has the be continuous weld. Spot welding it only allowed from new.

    If the backing plate (attached to the car-floor) is in good condition then I would run a grinder along the bottom edge of the new sill and fit it with the bottom edge about 3mm up, then run weld along the lip joining the two pieces.

    On one car that backing plate was so bad that I cut it off and welded a new plate in place making this slightly shorter. Then I put the new sill 3mm lower and the weld ended up on the 'inside' edge, ie, couldn't be seen when looking at the side of the car. It was a bit harder to do but made it very neat.

  3. Wozzaaah

    Wozzaaah The wizard of woz Staff Member

    This was discussed a while ago and probably several other times too. It's all in this thread including links to the MOT tester's manual.

  4. ade jiggly joggler!

    Posts: 7
    excellent - many thanks!
  5. Ade, (are you the Ade with a nice Capri?)

    I've done a few complete sills on various motors, admittedly not a Nova, closest would be a Nissan Micra.

    Anyroad, if it's a complete sill, as opposed to a 'cover sill' then the best way I've found is to get the door(s) off for access, trim out. Then go over all the flanges with a flap wheel to find the original spot welds. Using a proper spot weld drill (looks like a milling cutter) undo the spot welds. About now is a good time to brace the door apertures, you can get a purpose built tool for this, based on a builders turnbuckle, or just weld some scrap box section across the door apertures temporarily, this is to stop the pillars etc moving when you remove the knacked sill.

    You'll have to use a cutting disc or a jigsaw with a metal blade to cut the remains of the old sill off. Don't forget to offer up the new one so that you don't cut off more than you've got to replace it with;)

    I usually 'joggle' along the cut, my joggler has a hole punch which I use to put holes ever 25mm or so along the flanges, then clamp up, plug weld all the holes, and grind back smooth. A bit of filler, seam sealer paint etc and job done. Get it right you would never know it's been replaced.

    I usually cut a few 20mm holes from the inside, and blast the box section full of waxoyl, a wee bit diluted with white spirit to make it flow into the cracks. Plug the holes with electrical grommets from B&Q etc.
  6. Justme

    Justme Member

    Posts: 1,877
    Pwllheli Wales
    Good advice about the door jig had a few go wrong till I started to do that. Not sure if I am reading this right but it sounds like you are spot welding the bottom seam (which is ok) but the top joint is also spot welded but not at a makers join (or you would not have cut it of or joddled it) this is bad advice as the top join either has to be at the makers join & spot welded or seam welded. Some full sills will meet the makers join & some dont. On those that dont you must seam weld. Do it slowly in short runs moving up & down so all the heat has time to reduce to stop distortion.

  7. Yeah you're right, that read a bit wrongly.

    Let me expand: Yes, a plug weld along the flange at the bottom of the sill, and usually there's one such flange along where the door seal goes.

    I use the joggler to, well joggle where I've cut the rear wing panel, and seam weld that.
  8. Justme

    Justme Member

    Posts: 1,877
    Pwllheli Wales
    Cool I thought there must be some thing amiss. LOL

    I used to hate doing the rear panel bit as most time it was very difficuly to remove interior panels & trims & the makers have a habit of stuffing padding in the gap to reduce noise.

  9. ade jiggly joggler!

    Posts: 7
    cheers guys, that makes perfect sense.

    A bit worried about the door pillar moving - not heard of it ever doing that!

    It's a full skin I'll be replacing.
  10. Brace it before you chop the wreckage out and it'll be fine.
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