This week we arrive at part 18 of Marc Gruninger’s Hawk 289 FIA build…. let’s join Marc in the workshop

A place to sit.

The seats in the original Cobras were very comfortable, and were handmade from leather so were naturally quite expensive. These seats tempted me since Hawk Cars manage to reproduce the originals accurately. However, in the end my attention was drawn to the original bucket type used in the track cars. The bucket seats, although less padded, are more original for early racing-style Cobras, exactly as used by drivers like Ken Miles, and they certainly look like the part. (Of course they are also half the price of the posh seats).  These seats come in kit form and really need to be assembled to suit the person and their driving position. The kits are comprised of a seat squab frame base, four pieces of securing aluminium, a fibreglass bucket seat and a seat cover.

Pic one - Left, the seat frame with fore and aft aluminium fixing's riveted to it. The bracket furthest away is the front of the seat. Middle - the GRP bucket seat held in place with two 3/16 rivets so that the seat can be adjusted for final fixing. Right - side supporting aluminium brackets have been riveted on and the seats ready for its cover.

The fore and aft brackets were drilled as was the frame and they were then fixed to the frame using 3/16 rivets. The GRP bucket seat was placed onto the brackets. I tried to find the most comfortable position for the bucket seat before securing it temporarily with a pair of G-clamps. Two holes were drilled into the centre line of the seat and the fore and aft brackets. These were then secured with two large headed 3/16 aluminium rivets. This allows me to fit the side aluminium brackets and line up the seat so it is straight. Once it had been ‘eyed and straightened’ half a dozen times, I gave up and drilled the holes for the side brackets into the frame. I used four 3/16 rivets on either side to secure the brackets. These are supplied straight and need to be bent over to fit the seat. I did this using G-clamps and once held, holes can be drilled through the seat and into the brackets. For a start I secured the brackets with a 3/16 rivet on either side and this was good enough for the seat to be placed into the car, to check if the handbrake would miss the seat and that the driving position felt comfortable. Once I felt the seat was good enough I drilled and riveted the rest of the brackets. I used three rivets into the GRP seat aft and three rivets fore, while the side brackets required four on either side.

A bit of  back tracking

When the driver’s seat had been assembled and fitted, it was time to think about fitting the hard top to the car. Once I had tried sitting in the car with the hard top on and it became apparent that the view forward was somewhat restricted. I felt my head was too close to the headlining. After a few calls to Hawk Cars I decided to try and lower the seat. The seat has another inch before the bottom of the GRP bucket hits the floor of the car. I can also steal another ½ -inch by cutting a hole in the floor and letting the base of the bucket seat poke through. I measured where the seat had to poke through the floor and found a tubular chassis member in the way! This posed a problem since by cutting a hole I would damage the chassis member. The answer came in the way of a router. Because the floor is made of ½ -inch thick marine plywood sandwiched between two layers of one ounce chopped strand mat, I could route through the first layer of GRP and then on through the ½ -inch ply, hopefully leaving the last layer of chopped matt untouched.

Pic two. Left - Hole after routing. Right - Hole cleaned up and painted.

This would mean that the chassis powder coat would be left undamaged. The router did the job well and I reinforced the bottom of the hole with some chopped mat and a small amount of filler to smooth off the sides of the hole. Once it had hardened I sanded it and painted it black. The same hole was cut into the aluminium floor, which was then fitted back into the car. The seat rivets that held the GRP bucket to the 

aluminium brackets were drilled out and this allowed the seat to drop down. While sitting in the seat that had been placed in the car, I lent back and pushed it as far back as felt comfortable. Using G-clamps, the seat was temporarily secured and a few holes were then drilled so that it could be riveted permanently in place. The seat felt comfortable even with the hardtop fitted and also felt roomier. The rest of the holes were drilled and 3/16 rivets fitted.

Seat belts or harness?

I would like to fit four-point harnesses but apparently this can be a bit problematical for the SVA test, so instead, I'll fit the standard inertia seat belts and move over to harnesses after the SVA test. As with most of the stuff for the Cobra, the belts can be purchased from Hawk Cars. The only part of the belts that Hawk alters are the brackets that guide the belt over the shoulder, putting them where they should be. The inertia reels are fitted to the base of the SVA frame. The seat belt link arm bolts to a 7/16 bolt that passes through the floor and down through the chassis.

Pic three - This photo shows the SVA frame and the fixing points that are used to install inertia reels and belt hangers.

I have one problem when it comes to fitting the seat belt hanger. The bolts on the back are not captive, which means I cannot fit these after I have fitted the SVA frame cover panel that I made from aluminium. The answer was to cut a pair of largish holes, so the panel could be fitted over the belt hangers and then a smaller pair of panels made to fit over them and up against the aluminium panel. These do not look as good as the Kirkham Hawk demonstrator, but then again that doesn't have inertia belts anyway!  Before fitting the SVA frame cover panel I bought a length of rubber U-section from Baines in Tunbridge Wells that will fit around the panel edge. This made for an almost perfect fit when offered up to the SVA frame.

Pic four - A diagram showing the system I used to get around fitting the seat belt
hangers before I fitted the SVA frame cover panel.

Fitting the rear window

The rear screen is plastic and comes cut out 99.5% accurate, with just the final fit to be done. Once the screen sat in the hard top nicely I measured every two inches around the perimeter. This cannot be divided exactly into two-inch gaps so in certain places I had to give or take an 1/8”. The screen was removed from the hard top and placed onto a dirt-free, flat piece of hardboard.

Apparently a standard drill bit will bore through Perspex too aggressively and will cause it to crack, so the drill has to be backed off so that the cutting face will be at a less acute angle to the work piece. I used a 4.2mm drill bit that been backed off to cut all 54 holes. The screen was then placed back into the hard top and some tape used to fix it temporarily in place. The holes in the screen were then used as a template to drill in to the hardtop. Once all had been drilled and the tape removed, the screen and hardtop where given a quick brush off.

Pic five - The Perspex screen with most of the button heads fitted.

The fixing I chose to use were M4 stainless button heads. These bolts really need plastic washers but I didn’t have any, so for now I used the stainless ones that came with the button heads. One thing to watch out for is that its very easy to over tighten the fasteners and crack the rear screen. The screen itself really needs to sit on a thin rubber strip so that it will seat properly and seal. When I have the car painted I will use a rubber seal on it when putting the rear screen in again.

Words by Marc Gruninger

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