Series 1 bonnet

[E-ways]

I have recently acquired another, damaged, bonnet, for my 1964 FHC - the original, and its replacement, both having 'failed'
No.3 has been involved in one or two collisions, and, as a result, some of the internal diaphragms, have become unstuck, but the skin can be dressed into shape.
I note that early bonnets had these internal panels spot welded in place. Was the adhesive adopted, on later cars, for ease of assembly, for economy, to permit easier panel replacement, or for some structural reason?
I am inclined to have the loose diaphragms welded to the skin, and would appreciate any opinion on the advisability of that.

[christopher storey]

I do not think that any of the diaphragms, etc. were ever welded in place. The only bits that on the early bonnets were spot welded were the louvres . The appropriate sealant/adhesive is sikkaflex 221, and this is what should be used to reassemble a bonnet after repair

[Geoff Green]

Early cars had internal mounting flanges welded to the outer skin. The panels were bolted to these. After some time or mileage the spot welds would pull the skin down showing outer surface irregularities. Quickly the factory went to adhesive to fix the mounting flanges to the outer skin.

Geoff Green

[paulsco]

Strangely the flanges on my 65 bonnet are spot welded at the ends and glued in the middle.
This is clearly factory and I am 99% sure (multiple paint layers etc) that this is the original bonnet??

I have read somewhere that it is not advisable to weld the flanges as it can cause stress cracks in the paint, which is why Jaguar stopped welding them.

Paul

[Fixed Head]

Paul, The bonnet center sections with glued seams and spot welds at the ends only were later factory replacement parts. Not sure why they did it this way. So your center panel was probably replaced at some point. -Mark

[paulsco]

Thanks Mark,

How much later though and it seems a bit unlikely in my case; my car had at least 10 resprays in its life plus primers, all different colours.

I could trace each colour down to the metal, including the primer on both the bonnet and body shell?

Do you have any more information about these part welded centre sections?

Paul

[Fixed Head]

All I can tell you Paul is that the cars do not seem to have ever left the factory this way, but when I ordered a replacement panel (from Jaguar) in the 80s it did. We assumed it was to more accurately position the flanges, since they weren't assembling the inner panels at the same time, or maybe even to keep them from coming loose in shipping, but this is speculation. The replacement panels might have come this way from very early on. I don't know.

Ten resprays?!!!

[Fixed Head]

E-ways, to respond to your original questions:
The reasons not to weld the flanges to the outer bonnet skin include possible distortion, possible future diminished resale value since it won't be seen as correct, and the fact that it is not necessary structurally.
But the primary reason not to is that the flange dimensions and hole placement takes into account some space for the glue, and if you put the flanges directly against the outer skin to weld, you might find that your mounting holes for the inner ducts don't match up any longer, or that you have to elongate them.

[E-ways]

Thank you, gentlemen, for this variety of opinions, particularly to Geoff Green, who probably has identified the reason that the flanges were no longer welded, after it became clear that stress on the internal diaphragms would result in 'dimples' in the skin, where the spot welds were, whilst the adhesive spread the loading.

To those who doubt that the mounting flanges were ever welded, I draw your attention to the the photos of car no. 60, currently being restored, at Classic Motor Cars, where the spot welds are all too clear.

In response to Fixed Head, I agree that the shape of the glued flanges, and their hole placement, takes account of the thickness of adhesive. I am not sure whether it would be possible to re-glue, with sikkaflex 221, the detached flanges, without complete dismantling and sand blasting, which I am trying to avoid.

To those who still doubt that there was a combination of spot welding, and adhesive, even after the 'glue' was adopted, I draw your attention to the rear reinforcements, which have always been spot-welded in place.

I thank you for your range of advice, gentlemen, and I remain undecided whether to weld, or not !!