This week’s milestone activity, if you will, was painting the underside of the bonnet. Basically, the steps leading up to this point were media blasting the parts (last summer!), application of epoxy primer (also last summer!), following by a long period where bonnet fitment occured, followed by application of filler to correct minor issues, following by sanding with 320 grit dry, and 600 grit wet. The actual painting involved getting the paint booth cleaned out, heating the booth to 70 degF (no easy feat in the cold weather we are experiencing), following by 3 coats of Opalescent Golden Sand color, followed by 4 coats of clearcoat. For this go-around I only painted the center section and the wings.
HOW DID JAGUAR DO IT?
All of the above is fairly standard for painting a car. The interesting part, in my mind, is the tradeoff between current practices and how Jaguar did it. To answer that question took a little bit of detective work.
I have known for some time based on general discussions on forums like Jag-Lovers that Jaguar (the Factory) painted the bonnets in an almost fully assembled condition. Review of original unmolested cars indicates that most items under the bonnet received a coat of paint, including the bolts, screws, nuts, and oval washers that hold the whole mess together. In other words, the various bonnet pieces were assembled in an unpainted state. There are also indications that the bonnets were painted off the car, upside down, based on the fact that runs in the paint indicated so. Indeed, in Phillip Porters book Jaguar E-Type The Definitive History he quotes directly from Factory literature as follows (Ref. page 156).
The body is of monocouque all welded construction and several new techniques are incorporated in the welding processes, including the use of CO2 wire welding equipment. The various details and panels are built up in jigs into main sub-assemblies; e.g. dash structure, rear end structure, floor, etc., and the various sub-assemblies are then brought together in the main assembly jig. The completed body is then taken on a mechanical conveyor to the Paint Shop. During its passage along this conveyor various joints in the body are metal finished and the whole of the external contour is checked prior to painting. On arrival at the Paint Shop the body shell, together with its bonnet and sub-frame, is taken through the phospating plant in order to clean the metal thoroughly prior to the painting operations. It then passes through the underbody dip to ensure that the whole of the underside of the body is protected against rusting. This is followed by the application of two coats of primer, which, after baking, is followed by the application of sound deadening compound. The body is then mounted in a rotary transporter for its passage through the Paint Shop where it is flatted and given a sealer coat followed by two final coats of synthetic enamel. The painted body is then subjected to a detailed and minute inspection on specially lighted tracks after which it is passed to the assembly track.
I offer several observations. Probably the mosts obvious one is that if the bodies are assembled before painting, there are internal cavities that never receive paint. The sills are maybe the most obvious example and they are quite often found to be rusted. That said, the Factory did “phospate” the body (a chemical cleaning) and they experienced an “underbody dip” with an unspecified compound. These two steps could be expected to penetrate into inaccesible cavities. After that, the painting process was routine. Primer, sealer, synthetic enamal. An intermediate step discussed, while on the conveyor, is where lead is loaded onto the body and filed smooth.
So, to be authentic to the Factory process, one could take their assembled bonnet and just paint the accesible areas. Most restorers, including me, cringe at such an approach. A middle of the road compromise is to paint all the separate panels with epoxy primer, assemble the bonnet, and then paint it with color. What I have decided to do is the paint all the separate panels with primer, color, and clear coat. I will then assemble the bonnet and touch up the bolting hardware with color and clear coat. In the end, it will look “Factory” but the various pieces will be much better protected from corrosion. One area that is very hard to paint is the inside of the air ducts. I will use cavity wax on these areas.
One final area of discussion is the use of “body schutz”, “texture”, and/or “undercoating”. Undercoating, as defined my me, is a tar based mixture that is sprayed onto the underside of the car. I think “Ziebart” is a common commercial name for this process. There is no mention of such a step in the Factory literature. When done, I suspect it was applied by the US dealership or as an aftermarket process. All I can say is No Thanks! Regarding body schutz and/or texture, this seems to be a popular step with some restorers for the underside of the car. Again, I cannot see any reference to such a step in the Factory literature. Maybe the closest we come is the “underbody dip” step. My experience with schutz application is that is done with a rather crude paint gun that intentionally poorly atomizes the product such that it arrives at the metal surface in globules that dry with a texture. Not what I would call a “dip”. For purposes of durability, I have applied Glasurit Rocker Guard in the wheel wells. It is applied between the color step and the clearcoat step. It does not have any noticable texture.
So that sums up my thinking regarding how to approach painting the bonnet underside. I still have to paint the air ducts and diaphragms. Once these are done, I will assemble the bonnet, hopefully for the last time.
Post Script- Here is a period photo from Porters book showing a bunch of bonnets lined up in a warehouse at Abbey Panels, ready to be shipped to Browns Lane to be assembled into a finished car.