11 replies to this topic

[goat64]

Hello all.

Advice needed on replacing outer sill

 

Outer sill on driver side has crumbled away along half it's length.

It's the original as far as I know, on my 1976 850 mark 3.

6 flute, 4" wide (narrow) type sill.

Through the holes in it, the inner sill looks OK:  mostly still original paint !

I am a very amateur tinkerer, no experience of cutting out or welding.

Helpful local garage have had a look and are going to cut out and replace the whole outer sill (which I have on order).

Of course, if they find more going on once cut out rot, plans may change.

 

A couple of questions for the collective expertise:

 

1) What anti-corrosion coating (if any) would you apply to the "hidden" surfaces once old outer sill cut off. It seems too good an oppounity to waste, as once new sill is welded back on, no access to the closed space.  Worth getting replacement outer sill professionally powder-coated before welding in place???     Not sure if garage would be happy to do  it if I requested somethng specific, or if they would be happy to let me go up there and paint the inner sill with something before welding the new outer sill on.  Any "garegey" types in: what would you consider a reasonable planf or this?

 

2) The other (n/s) sill looks sound enough. I've treated a few small sections of superficial flaking with rust killer and will zincprime/red oxide/underseal (or wax) over top once cured. There are small holes (not the drainage flutes) at front and rear ends of both sills. They have little plastic drains or plugs in them. One (on the nearside, good sill) is missing, leaving a little hole, which is a bit rusty.  Can i justfill the hole, or should I try and get a little drain tube to fit in it????  I can't seem to find anything about these little plastic drains/plugs, but I may be looking for the wrong name!    The pic is the new sill  I'm expecting, with the 2 plugged holes circled. the slightly rusty hole in my "good" (nearside) sill is the oval-shaped hole at the front (nearest the jack point). To fill/ plug / leave open????

  Any ideas.

 

 

Cheers

 

Goat
 

  Any ideas?

 

    Is there any point, as welding will surely burn off most coatings anyway?

Attached Files

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[mab01uk]

Once the new sills are welded in place, inject Waxoyl (or similar) into the hollow sill box sections via the drainage flutes and any other holes that allow access for a plastic tube to spray/inject the rust prevention treatment in. (eg. seatbelt mounting bolt holes, etc.). Waxoyl creeps into all the welded seams and forms a flexible proctective coating but some will drip out for a few days afterwards, so you may want to lay something like cardboard sheets under the car to keep any excess Waxoxl off your garage floor or driveway. Place the Waxoyl can in a bucket of hot water to make it more fluid and flow better from the Waxoyl pressure sprayer, especially if you are working during cold weather.

Hammerite Waxoyl:-

https://www.halfords...-5l-141267.html

 

You can also use Waxoyl to rust protect other closed box section areas like the bottom of the doors via the small drainage holes and the rear inner sills from inside the rear seat side pockets/bins, etc.

Edited by mab01uk, 04 October 2025 - 11:12 AM.

[goat64]

Thanks for prompt response.

 

I have heard of this before and always been a bit reluctant as I couldn't see how it would reachall the nooks and crannies through small access ports like the flutes. But the "creep" theiry makes sense, and what a good tip about undoing mount mount points in isde the car to make temporary access ports too.

 

I have a nearly-full aerosol tin of bild-hambler wax spray, which seems similar to waxoyl, I think. The can certainly seems to have a very high pressure, very fine mist spray and a 15cm long flexible plastic tube. I'd probably use that up 1st. I do have a tin of waxoyl too, but no way to spray it in through small holes. I tend to paint that on to exposed surfaces.

[mab01uk]

You can buy this Waxoxl High Pressure Sprayer (see Halfords link below for details) but as said you usually need to stand the can of Waxoyl in a bucket of very hot water for a while to make the contents of the can fluid enough to spray into closed box sections easily via the sprayer extension probe with flexible plastic tube:-

https://www.halfords...jUkajYwJGwwJGgw

 

Bild-hambler wax spray, is very similar to Waxoyl and aerosol spray cans can also do the job but you do need quite a few of them for full coverage of a Mini, so it can be a more expensive way to complete the job.

 

Edited by mab01uk, 04 October 2025 - 12:45 PM.

[sonikk4]

The small holes are for the slinging frame when the shell was handled around the factory. I weld them up, i also remove the slinging brackets on the floor as the unwary try to use them as jacking points which they are not deisgned for plus they trap muck and act a focal for rust creation.

 

I used waxoyl in the past, it does a good job but Bilt Hamber Dynax or Dinitrol are much better. I use either of these for any resto i do now or sill repair.

[MatthewsDad]

There are various Bilt Hamber products. S50 is the stuff to use for injecting into cavities. The UC / UB products go on the underside and wheel arches.

Edited by MatthewsDad, 04 October 2025 - 07:19 PM.

[goat64]

Thanks for the pointers.

 

New outer sill arrived from Minispares ystdy. Was slightly concerned to see slight curve on the upper lip , but on closer inspection of the car, there is indeed a very slight outward curve on the upper lip of the sill, which I'd never noticed before.

 

Have chatted to garage up the road who are happy to cut out old, and weld in new for me. They say they routinely put "acid etch primer" on any  bare surfaces they find when old sill cut off. They also said very little point doing ANY pre-fitting treatment on new sill before welding as most will likely burn off when welding.

 

I hadn't realised the bild-hambler came in a different form to the UC can I already have. Presumably the S50 is a bit thinner / runnier.  I will invest in a few cans of that ,which come with 60cm long flexible spray nozzles, I think, so should make it easy enough to thoroughly coat inside the new sill spaces via the flutes and any other holes I can find.

 

Thanks again.

[Tupers]

I walkway paint the sill cavity with a zinc primer and 2K top coat and the welded areas with weld through primer. You might not bother if you’re patching up a ‘08 Focus but it’s definitely worth doing on a classic.

[sonikk4]

I walkway paint the sill cavity with a zinc primer and 2K top coat and the welded areas with weld through primer. You might not bother if you’re patching up a ‘08 Focus but it’s definitely worth doing on a classic.

 

100% with Tupers on this, i always prime and topcoat. If you are using a Magnum sill i would strip off the primer coat they use. In the past it was bloody awful and even the later stuff is debatable.

 

And just to throw a curveball into the mix, i do the same with Heritage panels as well. I have had over the years numeorus panels with spider tracks of rust hiding under the 'E Coat'. No point in my eyes changing a panel and not sorting it correctly to start with.

[goat64]

Thanks all for advice. The suggestion about "weld through" primer came too late for the new sill, which was welded on last week.

The garage assured me they treat all exposed surfaces with "acid etch primer" (?) before final weld. I have to trust them on that.

As soon as back, I used a left over can of S50 bild-hambler aerosol which comes with a 60 cm flexible nozzle with a 360 degree spray tip to poke up  through all 6 drainage flutes ass far as I could, spray as slowly withdrawing. I was amazed how effective it seemed: very high pressure fine spray coming out of adjacent flutes, adn after doing 1st couple of flutes, thick sticky black stuff started appearing at adjacent flutes. I feel confident there's enough int he "void" to make full use of the "creep" properties to cover the surfaces.

Also made use of the hanging holes to squirt stuff into.

Haven't made use of interior holes (seat belt mounts etc)  yet, but will prpbably get round to it soon !

 

I had no idea how much to use, so just did each flute until stuff started dripping out adjacent flutes whilst slowly withdrawing the long nozzle as I depressed aerosol.

One can of 750mls has done BOTH sills (the nearside one was a bit rusty but stil soid when poked with scrwdriver and bashed with hammer). and theres a little bit left !

 

I cleared out flutes gently using the nozzle so wax didn't set in the drainage holes, and did same a few days later once it had "set". It sets as a sort of semi-solid wax.

 

The garage charged me 5,5 hours labour, by the way, which seemed a lot to me, but as I have no grinding / welding skills or equipment, I had no choice, and no knowledge about what's involved. It would certainly take me a lot more than 5.5 hours, even if I had the skills / equipment. If it lasts half as long as the original (50 years), it works out at £25 per year (incl sill and S50), whcih makes it easier to accept !

 

Next job: leaky door panel: I will do a separate post. Thanks again to all.

[goat64]

Forgot to say... Re TUPERS post with pics of sill with paint....

Thansk v much for pics. I was struggling to work out where the "void" was once outer sill welded in place. Especially confused re why the "drainage flutes" didn't seem to be at the lowest point... had vsiions of water accumulating below the flute level. Your cpis of the inner sill make it so much eassier to visualise where the end of the flexible spray nozzle went, adn more espeiclly, wheich direction to aim for.

I had never heard of "weld through" paint before: what a good idea. I shall bear it in mind for next bit that rusts off!

 

Thanks

[stuart bowes]

I used waxoil based underseal on mine, obviously bare metal everywhere first, then etch prime, then the waxoil paint inside the void and on the inside of the new sill

 

when i had it all clamped up with the plug-weld holes all punched along the edges, I just used a small terminal screwdriver to clean out where the holes are, and plug welded it that way.  it's true that will melt the paint to some extent (and with the waxoil actually a bit of smoke as well..) but I checked regularly and kept blowing the airline into the vents to put out any flames

 

there's not much more you can do about that IMO, you want paint but you want it welded, and once that's done you can't get to it can you.  so yeah I'll pump a load of waxoil in there later as well later, that becomes a regular job i guess (what, like every few years maybe)

 

weld through primer has zinc in it as far as I understand so you might want to do the welding somewhere well ventilated unless you have an air fed mask, or at the very least wear a dust mask underneath

Edited by stuart bowes, 21 October 2025 - 09:56 AM.