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MG MGB Technical - Windscreen reassembly

Now that I've got the painting done I'm starting reassembly. I have the screen surround in bits, cleaned, brushed and polished. New seal and screws. Do I need to put any "gunge" anywhere before I assemble frame around the glass? If there is a site with details of reassembly that would be helpful. I'm already aware of using the right length screws in the right places.
Steve Church

Also, I have removed all the fittings from the frame. Do these need to be put back (with pop rivets), before the frame is assembled or can I install them after the frame is put together?
Steve Church

Steve, I have described it on my site at http://www.mgparts.co.nz/advice/technical-notes/fitting-a-windscreen/
It helps to do a dry assembly of the frame first without any rubbers or the glass to make sure verything lines up.
Paul Walbran

Then use plenty of gloop on the rubber when assembling the frame around it and the glass, it can need a team of horses to pull it together. Washing-up liquid is often recommended, but I found that dried out too quickly, Swarfega original (i.e. no bits) was much better.

Getting it back in the car with a new apron seal can be equally difficult, I have heard of people putting a ratchet strap over the screen and under the car to pull it down far enough to get the bolts in.

You need to be very picky about final screen orientation, the side rubbers should barely touch the quarter-light frames all the way up, if the engagement is such that the rubbers are compressed you can get the door skins cracking, from scuttle shake.
Paul Hunt

Paul H wrote " it can need a team of horses to pull it together" - too true. I used rope tournaquets and I couldn't believe how much force was needed to get the screw holes to line up. It's amazing such small screws can keep it all together.

He also wrote "Getting it back in the car with a new apron seal can be equally difficult" - with a new apron seal it seems for the first hour or two to be impossible that you could ever squash it down enough to get the bolts in. That's once you've persuaded the seal that it wants to extend forwards and not tuck under the frame. In the end my lovely wife climbed up in her stockinged feet and sat on the top of the screen frame (on a cushion) with her feet on the bonnet. Even then it was touch and go - well she's quite light!

Horrible job. Don't ever want to do it again. Oh, yes, as for gloop, I used a proprietary non-setting black windscreen sealer like item 370943238489 on ebay.co.uk. on the frame and glass. It is messy, but excess is easily cleaned off with a rag and white spirit. The sealer is nice and slippy so aids the job. I didn't put any under the apron seal, just some on the rubber gaskets under the screen legs. No rain leaks at all.
Mike Howlett

Thanks guys. I've done a dry run and notice that there are quite large gaps where the bottom frame meets the sides. I'm using the original brackets. I also offered up each piece of frame to the glass with seal. It didn't seem to offer up much resistance apart from the last couple of mm. That was dry. I expected it to be really difficult. Makes me wonder if the new seal is correct. I got it from the local mg specialist and it was labelled up as an MGB seal.

The scuttle seal still has some curl left in it and is not the original. I may get away with reusing it.

Thanks for the heads up on the screen sealant Mike.
Steve Church

When I removed my screen for painting the old apron seal stuck straight forwards, but I refitted the screen with it still on and had no leaks from there, although I may have used non-setting sealant under it. Pulling in a new seal is equally difficult, and trimming it to length needs thought and care as well, you may think it needs to go under the leg seals but it goes over the top, if it is below you can't get the legs down far enough to get the bolts in. Sealant is needed both sides of the leg seals.

When the glass was replaced the fitters insisted on using new glazing and apron seals, but still used the sealant under the apron seal, which they picked out bit by bit before the legs were anywhere near down far enough.

One thing I noticed with the new seal and glass was that there are now gaps at the bottom corners, which I don't remember from before, possibly due to the later glass which has cut-outs in those corners, and may be a fraction smaller.
Paul Hunt

Steve, Can you post a pic of the gap? It might help comment. Make sure your dry fit includes checking where the assembly sits in the car, with the pillar-1/4 light seals in place and lightly on the 1/4 lights as per Paul's advice. Make some alignment marks between pillar and wing with white marker.

As per my website, I use rubber grease on the seals to ease them in. I avoid sealer there as it makes it a total mission should the screen ever be replaced again.
The only sealer I use is between the corners of the frame, and down the outside corner of the bottom join and on the outside of the apron seal where it meets the pillar. (probably where your gap is?) I don't get leak problems.
I have found that sealing under the apron seal can actually cause leaks - if it is a type shich dries/sets too much relative movement between screen and rubber (vibration, expansion rates with temp changes).

A useful dodge to pull the screen down can be a long length of wood used as a lever, end tucked in under the rear scuttle, front protruding forward over the bonnet. You need a halper for this, but it's difficult to do a screen without a helper. Usually in the workshop we just get all hands to the pump and it goes straight into place.

Paul, The gaps aren't usually there when using AHH8227 (the version without the cut-outs) in the early frame, I think the later frame is OK with HZA5415 but can't remember for sure. Which version is yours?
Paul Walbran

AFAIK the frame is original to the car, 73 model. Certainly been with it for the last 25 years, and it didn't look anything like new when I got it.

In the attached the cut-out in the glass is arrowed - only just covered by the edge of the seal, and the gap I've referred to is immediately below the seal where it turns the corner, it's as if the lower rail has come further up the side rails than it should, which could be explained by the glass being slightly shorter top to bottom. However neither cause a leak.


Paul Hunt

Yes, that is the original frame, they changed for 1975 model year according to the books. That frame should have the early glass with no cut-away at the bottom corners, which from what you said above is not the case.
Paul Walbran

Whenever I see a thread about replacing the screen I'm immediately reminded to post my experience.

I bought a B with a cracked screen, so replaced it (without too much trouble, I have to say, although I used all the original rubbers).

About second trip out the glass cracked again, almost same place and top to bottom. Replaced it again (I was an expert by now), but wanting to find out why it had cracked again.

It transpired the problem was that the fibre spacers fitted between the legs and the chassis had compressed over time, probably as a result of getting wet. Tightening the bolts curved the screen too much with obvious results.

So, always worth checking the spacers and the fit at the legs.
3^114:0:2^128:0:2^84:0:4^127:0:3^69:0:1

As the new guy in my workshop found to my expense when I forgot to warn him ... :-(
Paul Walbran

Indeed, there should be no sideways movement of the screen legs in the body slots with no bolts installed. There is a thick packing piece and shims as required to pack it out correctly. However the packing pieces from some sources have a raised plinth with a part number on one side, and a boss on the other. These need to be ground off or they can cause the compression that 'arial small' refers to. Also the packing pieces don't have the tapped hole that is used to keep it and the shims in position when the screen is removed.


Paul Hunt

All these comments make me very glad that swapping between the cut down sports windshield and the standard one is a ten minute job on the MGA! Able I have special bolts with large turned heads, so I need a screwdriver for the grab handles and no other tools at a all, and each just drops into the slot and the bolts go back in. I use a piece of plywood shaped as a template to get the angle of the main screen correct for the side screens and hood when it goes back in.
dominic clancy

Getting the screen out and back in isn't that big a job on the MGB, I got mine out and back in single-handed for repainting the body in not much time at all. It's reassembly, and refitting with a new apron seal that causes the difficulty.
Paul Hunt

I've just had a look at the screen seal packaging. It says MGB 1963 to 1966. My windscreen frame looks to have 1979 moulded into it. Will there be any difference in the seal? The windscreen frame has obviously been replaced at some time.
Steve Church

If the earlier seal is thicker or larger than the later, then that may make things harder reassembling a later frame with the earlier seal. Even more so with an earlier glass in a later frame, as I understand it, because of the cut-outs.
Paul Hunt

Paul. if anything the replacement seal seems skinnier than the original so I don't think tbere will be a problem assembling. I did a dry run last weekend and it was an interference fit. I'll hopefully get some time tomorrow to put it together.
Steve Church

The early glass in the later frame would be tight indeed, perhaps tight enough for the frame to put too much pressurer on the glass and crack it.
Paul Walbran

Ok. Have now assembled frame around glass (complete with seal). Took about 10 minutes, on my own, no straps or belts. Just a little washing up liquid. Now I have a loose fit between the frame sides and the seal (seal lip is about 5mm away from frame edge, and I can push it easily towards frame....sorry but pic I took was not in focus). As I mentioned above the frame appears to be from a '79 model. I am questioning if there is more than one design of seal.
Steve Church

A factor of the skinnier seal? Only one part number is listed in the Parts Catalogue for the whole of production, but there is nothing to say what is currently available is 'right', witness the boot/hatch seals.
Paul Hunt

Hmmm...I'm going to have to make do with this one then. No point in trying another, it could be just as bad. Looks like I'll need to disassemble and clean off the washing up liquid and inject some sealant into the loose bits. Judging by the slightly corroded state of the lower joining brackets it seems that even the original had leaked. I suppose I have to look on the bright side in that it wasn't difficult to put the frame together. Putting the screen on the car may be another story however!
Steve Church

Mike,
Do you think that the screen sealant you used could be used to fix the screen seal in place and stop it creeping away from the frame? I'd rather not have to get two tubes of "goo". One to fix the seal and one to seal under the frame/scuttle join. It would be helpful if I can use the same one.
Steve Church

Make sure that with the legs in the sockets there is no side to side movement of the frame relative to the car, or when you tighten the bolts the glass can crack. If there is then you need more shims between the inner faces of the legs and the sockets.

You may find the opposite problem though and find you cannot get both legs in, in which case the shims must be reduced.

The shims and the spacer are normally held in place when the screen is removed by a screw between the two bolt holes.
Paul Hunt

Thanks Paul,
I'm hoping that the distance between the legs hasn't changed as I am using the same frame brackets, but I will check. As you can see from the attached pic, the PO had done some "modifications" to make fitting the screen easier. At least that's what I assumed they were for. These included drilling out the threads in the frame legs and fitting a bolt and nut as well as hacking a hole in the rear of the wing. Not ex/ctly subtle is it?

The pic also shows just how much gap was between the bottom of the side frame and the top of the wing. This was taken before I stripped the car down.


Steve Church

Hi Steve. I don't think windscreen sealant will act like an adhesive. It doesn't really set but remains slightly soft for ever. Of course this allows it to fill any tiny gaps where water might creep in. Whether it will stop your rubber from moving, I'm not sure. Sorry I can't be more helpful but in my limited experience I've never come across a screen frame that was slack like yours seems to be.

Regarding the "mod" done on your car, shown in your photo, I understand why it was done, but by gum it's crude isn't it! It's possible that the threads in the soft screen legs were knackered by levering the frame down with a screwdriver in the holes. I've seen that happen.
Mike Howlett

Thanks Mike, I'll get some of the stuff you used anyway as I'll need it for the bottom of the screen/scuttle. I'll use something else for the glass seal. I've loads of white PU and silicon but think that will look a bit out of place!
Steve Church

Either that or the bolts stripped/sheared, I've heard of someone else having to remove the cover panel to get at them from the 'back'.
Paul Hunt

I'm doing a final ssembly of the screen frame. How (and when) should the scuttle rubber be fitted? Should I fit it in afterwards (as one of John Twist's videos shows) or put it in as theframe is assembled. Also what is the arrangement around the bottom of the screen pillar. Where is it cut to?
Steve Church

If the ends of the channel it slides into are closed off by the side pieces (I can't remember exactly how mine was done) then it may be easier to do it before the side rails are attached.

The ends are not strictly logical, it seems that it should go underneath the feet, but that stops the screen going down as far as it should:


Paul Hunt

It goes above the foot seal. Be careful not to cut it too short, it might shrink a bit after pulling in. It's best to pull a bit more through than you need, then push back and trim, ditto at the other end:


Paul Hunt

Thanks Paul. Seems like an opportunity for a few gaps. Plenty of sealant then.

The frame looks to have been polished. Is that fresh anodising or did you strip it and polish? I stripped mine and have a brushed aluminium finish now. Used a green scouring pad. Then waxed it.
Steve Church

Not mine but John Wynne Davis, I was helping him solve the problem and he sent me before and after pictures.

When I restored mine 25 years ago I tried various things to polish the frame but nothing made any difference so I left it as it was. Still the same now i.e. no worse.
Paul Hunt

This thread was discussed between 06/11/2014 and 19/11/2014

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