1963 FHC- Fitting the Bonnet- Again

I see that it has been over a month since my last post. Where in the hell did the time go? Well, an interesting thing happened. I got vacinated against Covid. So did my wife. She in particular, with underlying conditions, had just barely ventured out into “the world” for over a year. You might say there was some pent up demand. We haven’t gone crazy, mind you. We went into the grocery store on a Saturday, when it was somewhat crowded. She said that made her feel a little nervous. You want to know where her happy place is? The lawn and garden center at Lowes Home Improvement! And it’s spring. Oh baby, I have been sucked into the maw of spring planting fever. We have a raised bed garden that needed attention, including the irrigation system. We planted bulbs in the yard. And roses. And so on and so forth. Not limiting ourselves to gardening, I tackled a repaint of our wrap around porch. It’s all in the prep, baby, and I’ve got a full week invested in sanding and filling peeling paint and wood rot. Kind of like working on an Etype!

So yes, I do have some progress to report but not as much as I would like. Looking back, the main effort has been fitting the bonnet. Again. This time my goal was to perfect the shut lines at the cowl and sill extensions. The first step was to reinstall my spare engine and transmission into the car so as to properly flex the body. My previous experiments indicated it does make a difference. Once I had the weight on the car, I started to evaluate the fit of the bonnet to the cowl. There is a gap to be considered. There is also the transition alignment, which you can think of as if you lay a flat edge across the gap, are both sides of the joint at the same height. For short, I’ll call this the alignment.

Even though I had worked very hard during my previous bonnet alignment, before I painted the inside, when I fit it again there were still issues. When I started, none of the hardware internal to the bonnet had been tightened. I basically attached the hinges and the bonnet latches and pulled the gap and alignment into the best position I could obtain. In the case of gap, there is always one spot that will be the closest. Short of removing metal, that spot sets the fore/aft position of the bonnet. There is also left/right. Obviously, you want to center the bonnet on the cowl as closely as possible. Once I got the gap and left to right where I wanted it, I proceded to tighten the various bolting hardware. Note the bonnet balance links should not be installed at this point, as they tend to pull the whole bonnet forward. Once I get everything tightened up, I installed the balance links. I was pleased to find that this installation did not significantly change the gap at the cowl. Note that I tried various combinations of shims under the bonnet hinges as I worked toward a good fitment.

What I did notice was that the alignment at the cowl was not good. You can change the vertical position of the bonnet at the cowl by adjusting the bonnet latches. In my case, I found the alignment was good at the two joints where the center section meets the wings. It was low as I moved towards the power bulge. I didn’t want to raise the bonnet latches any more so I hit upon another solution. I cut some thin rubber strips out of inner tubes and basically shimmed up the rubber gasket that seals the bonnet to the cowl. I was surprised to see that I could raise the bonnet center section using this approach and bring it into good alighnment. I used 1 or 2 thicknesses of rubber to obtain the desired result.

For the record I use premium 3M body filler as a technique to perfect the gap. I have a couple of ground rules. I use the absolute minimum required, i.e. I work very hard to get the metal surfaces in alighnment before I resort to filler. I avoid adding filler to the back edge of the bonnet, as it will either be a thin application that will break off or a thick application that looks awful when you open the bonnet and examine the thickness of the back edge. Rather I add the filler on the cowl side of things, where there is a generous blunt edge to work with, basically the back side of the channel that the gasket fits into.

My general approach is as follows. I remove the rubber gasket and the shim strips. I lock the bonnet down with the bonnet latches. Then I pack the joint with filler. I keep a close eye on it and as soon as it starts to firm up, I run a razor blade down the joint, using the back edge of the bonnet as a guide. My goal is to cut a line that is at least wide enough to insert 1 thickness of 80 grit sandpaper. When the filler is fully dried, I proceed to carve out the gap. The first pass is with 1 thickness of 80 grit. The 2nd pass is with 2 thicknesses of paper. Then 3 thicknesses and finally 4 thicknesses. I have found that 4 thicknesses gives me the gap I want. As noted above there will be one spot where you are metal on metal. And in general, the maximum filler thickness will be no greater than 1/16″. At some point, you will open the bonnet and find that the filler doesn’t look so great down into the gasket groove. This can be fixed with a thin dressing of filler. I usually use a razor blade as my applicator, as it seems to give me better control than the heavy plastic spreaders normally used. When you are done, the groove for the gasket will be smoothed off and unremarkable looking. And of course you are going to add a rubber gasket, which will hide the groove but I like to work on the premise that it should look good with no gasket installed.

Once I get the gaps looking good, I reinstall the rubber gasket and my shims. I lay a strip of tape over the gasket and latch the bonnet back into position. The alignment should be very close but as a final step I lay filler on both sides of the gap. I then “block” the cowl/bonnet surface to get both mating parts in perfect alighnment. There will invarably be some back and forth to keep both your gap and your alignment working well together. When you are done, you will probably have a very crisp 90 degree edge at the gasket groove. Break this edge just ever so slightly with 300 grit or so to mimic the rounded edge of sheet metal bent into a 90 degree angle.

The above process took me many manhours to complete. I realize that are some consider this cheating and there are some that would attempt to do this entirely with metal. Sorry, I’m not good enough to do it with metal and I see plenty of filler being used by top end restoration shops.

By the way, I used this technique on my 67 2+2. A decade later, I have not had any failure of the filler in this type of application.

Once I had the gaps whipped into shape, I sprayed the car forward of the doors with Glasurit high solids urethane primer. I then “blocked the bonnet, which in my case means I sand it with 320 grit paper dry and look for high and low spots. I probably did this cycle 4 times until I got the surfaces in good shape. This is what is going on in the above photos. This is tedious work but is part of the process to get a perfect substrate for paint. Next I plan to switch to wet sanding the overall car with 400, 600, and 800 grit paper. When I am done with these steps, I will be ready to apply color and clear!