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MG MGA - Cracked windscreen

After 13 years the top corner of my windscreen has cracked. I just noticed it when I was washing the car and had taken the sidescreen off. Its a laminated screen so I'm not particularly in a hurry to replace it. I notice Moss have Triplex "Pilkington" ones available which I think I bought last time. I struggled to get a good fit with the frame last time and after someone in Malvern did a poor job I eventually got Les at Bob West's to put it together again which he did beautifully (although why has it cracked!)

In case I struggle again to do a good job can anyone recommend someone to reassemble it in the SW of the UK. I'm in South Wales? I was only just thinking that I didn't have any major jobs to do on it!


John Francis

They usually crack when someone uses the top of the screen as a handhold when getting or out of the car. The frame will flex, the glass doesn't!

The important details when reassembling are to clean all threads and to make sure your new seal is the correct thickness, then its a one hour job for one person and a ratchet strap or two to hold things together until all the screws are tight.

The screens from Bastuck were good too
Dominic Clancy

The original rubber mounting is very rigid and any variation in pressure can break the windshield. For trying to be a purist in the restoration it happened to me and I replaced it with special silicone for windshield assembly. No problem since then.
Gabriel Martínez

I have bought a new Pilkington Triplex screen from Moss. It is 7mm thick which is thicker than the original which was 0.25" or 6.25mm according to Barney's site. My last screen was a Pilkington (NSG) one which was only 5.6mm thick. The glazing rubber from Moss is neoprene which is not very good and I have been told that it is too soft and can lead to the glass touching the frame which tends to crack the glass. I have identified some 1.5mm thick glazing rubber which I hope will work. The slot in the frame tapers from 10mm down to 9.5mm and I hope the assembly will take 0.5mm compression. The only other thickness of the glazing rubber is 1.0mm.
Gabriel do you have any details of the silicone you used and was it a messy job? I imagine trying to centre the glass in the slot needed some care.
John Francis

It's easy but you have to put support points for the glass around the frame, which can be made of hard rubber, hard plastic or wood of about 5 cm. long (I don't remember the width, but it is obtained by measuring the section inside the frame), two at the top and bottom and one on each side. I don't have photos or exact measurements but with the frame disassembled it's easy to get them. I don't remember the brand of silicone but that would be different in each country. It is black window mounting silicone. You have to assemble and tighten the frame with the fresh silicone, recently applied so that the tensions are balanced and do not harm the glass.
Gabriel Martínez

I took a couple of screens apart in the early 1970's and they both had wood spacers along the bottom rail, so I suspect they were placed in there by the factory.
John Bray

I have today managed to re-glaze the frame. I had to use some 1 mm glazing rubber at the top and bottom and some 1.5mm rubber on the sides. As a word of warning the tolerances on the glazing rubber is +/- 0.4 mm. So the 1mm rubber was 1.2m thick and the 1.5mm was 1.65 mm thick. I did buy some 1.5mm from another supplier and it was 1.85mm thick. I used the suggestion from Dominic with ratchet straps to help hold the top and bottom channels in place and to apply some pressure to get the glass and rubber to slide into the channels. I used some wetted washing up liquid as well. The tricky part was centering the glass in the channels and getting the mitres to line up nicely. I found that mounting the glass in the channels without rubber and centering it allowed me to use masking tape across the channel and the glass to create a line to work to. It was best if the line was about 20cm from the ends of the channels. The get the mitres to line up it is best to leave all the corner pieces loose and gradually tighten them up. I still found it impossible to get one of the lower corners to line up perfectly and the top mitres are not parallel. See pics (before trimming the rubber) I used different length screws for the corner pieces in some places on the side channels. The original 5/16" long screws were too short in some places and I used 7/16" screws. NTG have the correct c/sunk pozi screws in different lengths. A bed makes a good soft flat surface to assemble it although you have to kneel!

John my understanding is that the new screens don't need the wood spacers as the screen is shaped along the bottom edge to relieve the corners.





John Francis

This thread was discussed between 17/05/2023 and 16/06/2023

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