Very early 1960's Mini sills and A posts were foam filled at the factory to try to cure water leaks. The early flat outer sills were constructed differently to later Minis as part of the floor and had no external vents or seams, so the lap joint which leaked, was inside on the inner sills under the carpet.......an error by Issigonis who had designed it that way to make construction of the car simpler in third world countries. The theory was the complete one piece floor with outer sills incorporated could be placed on the ground and allow the body panels to be constructed on top with minimal complex factory jigs or tooling required. One of the early 1960's Mini books did tell the story of leaks and foam in some detail, including the figures on improved torsional body stiffness achived.
Sometime ago I contributed a rare scanned copy of the BMC (Austin) Service Memorandum A1277 - A356 to the Mk1 website which is a collection of Austin service memoranda dating from August 1959 through to 1961, covering those chaotic early days when the problems were being found in the new car and solutions had to be found quick.
BMC Document Archive (scroll down halfway to blue covers):
http://mk1-performan...actory_docs.htm
The water leaks are covered for Dealers to fix and the foam welding problems are pointed out with diagrams.
See page 13 here:
http://mk1-performan...-61mini-pt4.pdf
Factory foam in Mini's was discontinued because of the cost and as only a tempory measure once the water leak had been fixed by a redesign of the floorpan/sills. Also the health and safety risk during welding was perhaps a consideration (see link above). BL are reputed to have bought back some of the early foam filled cars in the late 1960s to investigate, and found negligible corrosion in the foam filled sills.
I have personally restored several early Mini's with foam filled sills and the main reason they had survived so long was because the foam filled sills were still very solid and reasonably rust free as air and water had been excluded......much more so than younger later open vented sill Mini's.
With the later vented outer sills with external lap joint if you get water up inside them most of it will will run out again onto the ground below. Providing it's got a good coating of paint and waxoyl injected inside (like some modern cars), rust is minimised but only a few Mini enthusiasts bother to do this and it was never done at the factory so rusty sills are common !.
If you fill the later sills with foam it will retain the water and cause accelerated corrosion and be a nightmare when it comes to welding.
Edited by mab01uk, 06 July 2014 - 10:51 AM.
