Anyone else have problems with their roof lining becoming pressurised from above and popping down?
I must be getting air forced up the pillars (front, middle or rear) which pressurises the cavity between the roof-lining and roof, causing the roof-lining bows to invert under pressure, with the result being the roof-lining resting on my head, still under pressure.
It is the third time it has happened, which needs the lining to be removed, refit the bows, and replace the lining – not my favorite job. Initially I thought it may have been my workmanship, but now I am not so sure.
It all happens at about 110kph, with a bang.
It is a standard lining from one of the Mini suppliers, which I have glued in all the way around, then fitted the window and door seals.
The body has had a round nose conversion and the second engine fitted in the rear.
Can the front pillars become open to wind pressure under the guards or bonnet?
Is this problem unique to me with the Twini, or have others experience something similar?

I would guess that you are getting air up the rear pillars from the rear engine bay.
The factory used to stick sponges into certain cavities to stop draughts and create rust. The corners of the original parcel shelf had a sponge around the edge to stop the draught from the open boot from blowing up the rear pillar.

The front pillars have a filler panel that attaches to the top corner of the A panel to stop the pressure from under the front arches blowing up the pillar. These filler panels can rust out.

I suspect the normal foam would still let air through (like and air filter).
I removed the normal foam and filled the gaps with some of the expanding foam, which I doubt would let the air through, but I guess you only need a small gap, and the air will get through under pressure and build up in the roof cavity.
I suspect this is the problem, but checking if anyone else has had similar.

I think the lack of replies is due to the demonic speed the twini is capable of , your average punter probably never reaches those speeds.

Part of the problem could also be caused by a pressure drop in the cabin. if air under the floor pan is travelling fast enough, and there is a hole on the floor pan that the air has to travel across, it could siphon air out of the cabin.


(Bernoulli's principle)

It could be the underfelt thats glued to the roof is old and not holding the bows tightly in position because when one drops the others follow.

There is no underfelt on the roof, but the signs are that it was there once.
I think I will seal the rear pillars with sheet aluminium and sealant to make sure no air pressure can move from the engine department and up into the roof cavity.
Thanks for the ideas.

Nah,
More likely your roof has been jumped on at some stage and the metal is fatigued and stretched. Air flowing on the outside is causing your entire roof to cave in taking the hoodlining with it.

_________________
1970 Cooper S ex-Bathurst & ATCC
1964 Austin Cooper S ex-Group C race car
1967 Morris Cooper S ex-Group B
1962 Mini Speed sports sedan
1968-71 ex-Peter Manton Shell car

I'd be stabbing a biro in to the middle of the fabric right above the bottom of the handbrake. And then removing it.

Problem solved.