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MG Midget and Sprite Technical - GRP doors twist

i have GRP (fibreglass) frogeye doors.
i can get them lined up and a reasonable panel gap at the front, but along the length of them they twist, meaning that at the back of the door at the bottom it sticks out by about 10mm proud of the sill/rear body.

Is this a common issue ? if there any way to apply heat or something to get it straight ?
if i press with my hand on the part that sticks out it will go flush...
maybe make some lock mechanism that has a latch top and bottom which pulls the door into shape ?
Andy Phillips

Andy,

I had problems with sags in frogeye front and rear panels new from the supplier and resorted to supporting the area with a jack and wood slats and applied heat from a fan heater to warm the area and on cooling the FB would take the new shape. I expect you could do similar and warm the panel when held in the right position. I'm not sure what the panel temperature got to but from memory it was too hot to touch comfortably so probably 60C or more.
David Billington

GRP stays 'plastic' for some time after manufacture depending on the ambient temperature that is evaporating the plasticisers in the resin. As David says hold it in shape and warm up. This will make it more bendy and also evaporate some more plasticiser. Then allow to cool down in the new shape while being held. Trick is to get it right first time as the more you heat it the less plastic it becomes in the long run as you evaporate more and more plasticisers. Also best with GRP panels to fit immediately and store correctly so you can bend them when new and can bend them wrong when storing.

Also remember if you get it too hot it will burn and then its totally denatured (kna&£*rd). No plasticisers left after that point.
Dave Squire (1500)

doors are about 3 years old, fitted originally by PO...
they have peen painted with two pack primer, then acrylic colour. then two pack laquer.....
does this mean the plasticisers will be locked in ?

thought i would be able to adjust the doors better when i refitted them.....
Andy Phillips

No harm in giving it a go, just be careful when bending them, if they sound like they are crinkling or russelling it will be the fibres beginning to delaminate (or the bonded sections of the inside and outside of the door coming apart) so best stop and see what's happening. Delaminated GRP is glass fibres with no plastic holding them. (all floppy and a pig). There will be some plasticiser still there after 4 years its just a matter of how much and of course its a bit warm in Thailand at times so how much is the question.

If that fails then another approach is to bend the doors to shape and fibreglass some stiffeners into the inside of the doors to hold the shape. (a thin bit of light wood like a piece of thin ply on edge to make an upright angle to the inside of the door covered in GRP and bonded to the inside of the door would do it). You would also have to have the time and patience for the new GRP to cure enough to hold the shape before removing the clamps holding it in shape as well as the existing will continually spring against the new and you need it to be cured enough to hold the old. If at this point is there anyone local that can advise? Its a bit of an experience and skill thing not something that is easy to just do.

(I laminated boats and canoes for a living in the 70's but it is all personal skills and experience that count when repairing the stuff)
Dave Squire (1500)

i'll try that then, that should work (glassing in strengthening ribs)as i can relatively easily push the door into shape with my hand.
And the good thing about this method is i dont have to touch the outer skin of the door with my new paint on it.

I have two fibreglass companies that are suppliers to my business, so shouldnt be a problem....

Many thanks for your advice..
Andy Phillips

This thread was discussed on 22/04/2013

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