We stripped the underseal from the floor/chassis and found the steel underneath was deeply pitted, mainly on the chassis but less so on the floor. It seemed that the underseal had dried out and had allowed moisture to get underneath which let rust take hold.
However, the original steel is quite thick and there were no perforations in the chassis. In fact, the only perforations were on the floor in each of the corners and where bodged repairs had been made. For this reason we decided to repair the floor with floor sections rather than complete floor halfs.
Wire brushing couldn’t get into the pits, so we bought some Bilt Hamber Deox Gel and applied it as per instructions:
It was left for 24 hours, wrapped in cling film to stop the gel drying out. After the first application, there was considerable improvement but nowhere near good enough for an acceptable paint substrate:
It took a further application of Deox Gel, lots of sanding and wire-brushing, then further treatment with citric acid and even more sanding and wire-brushing before the chassis & floor were near acceptable. Eventually we were left with just a small amount of rust to remove before priming:
As shown above, we used front quarter outer repair panels and rear quarters rather than whole floor sections. In practise, however, about 75% of the floor has been replaced.
One issue we had was that the rear LHS cross member was out of stock from our usual suppliers and one gave a lead-time of nearly 6 months. So decided to fabricate own panel. Its not such a difficult panel to make, just needs a bit of careful folding and trimming. Here it is trial fitted prior to trimming and finishing:
And the finished panel tacked into position, c/w captive nuts welded in:
The floor sections were fitted with reference to this drawing found on the ‘net, taking care to ensure the body-chassis mounting holes were in the correct position. Before welding in fully, the body and chassis were mated as a final check. There were some holes that needed to be repositioned but overall there was a good fit.
With everything welded in, the coatings were removed from the repair panels and the whole chassis given a final sanding down and degreased with thinners.
One last bit of welding almost forgotten about was to add a couple of brackets for the battery restraint:
With everything as clean as possible, the floor/chassis was given a coat of Epoxy Mastic 121 two-pack paint (brushed on). This paint is excellent: I’ve used it on two previous restorations and found that it sticks to bare steel like no other and is tough and flexible when cured. It seems expensive but when you consider that one coat gives 100% coverage compared to say, Hammerite, that will need two, maybe three coats, then it works out good value.
The welded joints and flanges were then seam-sealed and the underside, frame head and rear forks were given a light coat of etch primer then two coats of anti-stonechip:
That just leaves the front of the frame head to treat & paint – this’ll get done when its off the jig.