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MG Midget and Sprite Technical - A-Post drainage. Maybe B-Post too.

In December 2012, in the thread entitled "A post/lower hinge interior pictures?", we got around to discussing drainage. --- See picture.

Guy mentioned that he drained his A posts through the sills, with holes at the bottom to let the water out. I wondered if a plastic pipe could be run down through the sill, to prevent any water entering the sill from the A-post, and thereby eliminating the need for extra drain holes in the sill.

Then in March 2013, in the thread entitled "Collision repair - A pillar" , G Smith of Fife, proposed his idea. This was , --- " to bore a hole through top of sill then roll edge of hole down using a punch to make sort of spout, butt steel tube (larger than hole) to underside and weld. The tube would fit snug through a hole in bottom of sill and be welded here too." He wondered if anyone had given any though to this method.

I replied, "You'd want to make sure the entrance to the pipe was flush with the sill, so no water could lay around the entrance. Is that what you mean by rolling the edge down? So you'd insert the tube from below, and hold in place whilst you weld. Sounds like a plan."

Well I finally I got around to doing something about it.

Instead of inserting the pipe from the bottom, I decided to make a plate with a punched hole in it, and weld that to the top of the sill through which I'd already drilled a hole large enough to take the pipe and countersink. On a new sill, I would let the drain plate into the sill flush. But on this, I decided to just weld the plate onto the top of the sill. Lazy, less hassle, but just as effective.

The following posts are the results of my efforts.

Lawrence Slater

Made the plate using a bolt as a punch and a countersink.

Lawrence Slater

Welded pipe to plate.

Lawrence Slater

Welded plate to sill.

Lawrence Slater

Coat of primer. To make me feel better, and it look better. lol.

I might add one just in front of the A-post

It would be useful to add one to the B-post too. But the access in the B-post is restricted, and as I haven't got the wing off, I'm not taking it off just to do this.

Lawrence Slater

I like the idea but I doubt my metalworking or welding skills are up to it at the moment.

If I may make one comment, unless it was going to foul something else, I think I would have let the drain tube extend perhaps 1/4 inch below the sill. That way water shouldn't cling to the underside of the sill but would drip straight off, especially when parked after a wet run.

I'll be interested to see how this thread develops as my first reaction is to plan to incorporate Slater Drains when I get round to working in that area.

Colin Mee

Tidy job. Certainly a design advancement on mine! The sill, of course, will still benefit from plenty of drainage itself as however hard you try, water will still get in there.

But I don't see the point of a second one in front of the A post as that area just drains out of the panel gap anyway
Guy W

Yup Guy, I agree, it should drain under the wing. But I wonder if when theres a blockage, wet leaves and the like, some water corrodes the front of the a-post from behind the wing. Another hole might help in the event that laziness prevents clearing the gap under the wing.

Colin, initially I did extend the pipe. But it looked better flush. and besides, I don't imagine a constant drip of water from the a-post. I'm going to seal it tight to stop any flowing water, and there can't be that much in condensate. -- I hope.

Clearly water get's in somehow, but I don't think it's that much. Just that over time, it rots the bottom of the a-post.
Lawrence Slater

Actually, I should say. On a new sill I would punch the hole directly in the sill, and weld the pipe to it, before installing the sill. -- As G Smith of Fife, proposed.

Maybe someone could make sills incorporating drain pipes?
Lawrence Slater

If the behind-the-wing area gets choked with leaves/silt etc, then the drainage hole is going to get blocked as well anyway. I like the A post one, but I think the second one is a waste of time.

After all that welding, how are you planning to give the insides and back of the weld areas a coat of paint?
Guy W

I'm not so sure the extra hole would be a complete waste of time Guy. All the wet stuff, eventually saturates, and if the excess water can't escape under the wing, I still think it would drain down the plug hole I'd created. And with a 5/8" inch hole to poke up, it should be pretty easy to hook a lot of stuff out. But I concede, it really shouldn't be neccessary. Hence my only doing the one hole inside the A-post, and I don't think I'll do the one in front of the A-post.

But if fitting new sills, I would. 10 mins to punch a hole in the top of a new sill. Say 1 min to drill a hole in the bottom, and say 10 mins to weld the pipe to the top and bottom holes. A few mins grinding. Circa 30 mins of easy effort.

The B-post is another area I'd definitely do too -- on new sills, or if I had access. On my Sprite, and on this midget, the bottoms of the B-post rusted. Water gets in, in a variety of ways. Once in there, it rusts down through the sill, in through to the inner sill, and out to the door shut. A piped drain there would be beneficial I reckon. So on a new sill, or if renewing the lower wing section by the door, I'd put a drain there too.

How will I paint the insides? I'm going to paint as much as possible prior to fitting the skin. The with the skin in place, I'll wire brush the weld areas clean, and weld. No doubt that will burn away some of the paint, so I'll inject through one of the lower door hinge holes or through the hole the gives access to the door switch wiring.

I'm using zinc plated/coated sheet, so hopefully where I can't get paint, the metal will still have some protection.
Lawrence Slater

But going back to the drainage, if you look at my last picture, you can see the lower hinge, top reinforcing plate. Note how it is completely rust free.

The was no evidence at all, of water coming in from the top, and sitting on this plate. All the rust was below the lower half section of the hinge plate. Condensation would surely have affected the top section too.

Whilst condensation must play a part, especially behind the skin where it sits on the A-post flange, I'm of a mind that much of the water gets in from the outer seams at the bottom of the A-post. Either way, however it gets in there, if it can get out as fast as it gets in, then it won't do much harm, -- if all the surfaces are coated in paint and or waxoyl or the like.

So thanks for mentioning that you'd drilled your sills Guy, it was the catalyst for my doing this.
Lawrence Slater

This thread was discussed between 08/06/2013 and 09/06/2013

MG Midget and Sprite Technical index

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