Authentic Cobra How-To (289, 427, SC 427)



1. Original Specifications


2. Bonnet & Scoop Rivets


3. Exterior Fittings


4. Dash & Instruments


5. Interior Fittings


6. Boot Fittings


7. Engine Bay


8. Colour Codes



Bonnet & Scoop Rivets

Original SC 427 & 427 Competition Cobras carried pop rivets on both bonnet & bonnet scoop.  289 & 427 street Cobras did not have any rivets. The rivets were used on original competition cars to stop the front edge of the bonnet from peeling back at high speed.

There were a number of rivet patterns used on the original cars.  The most popular patterns are what enthusiasts call 15-1-15 pattern & 12-1-12 pattern.

ERA use a pattern that is essentially an 8-0-8 pattern which is popular with replica builders due to use of less rivets.  This pattern favours the use of larger rivets or button(dome) head screws.

The original vehicles were fitted with 1/8” aluminum pop rivets on both the leading edge of the bonnet and on the bonnet scoop flange.  Replica builders quite often prefer to fit rivets like 3/16”, especially when using 12-1-12 & 8-0-8 patterns.  Alternatively you can use stainless rivets, remove the shank, polish them up and glue them in with silicone.

Stainless Button(dome) head screws are also popular in the same 3/16” size.  These can either be drilled and tapped into the fiberglass or drilled and inserted all the way through with nylon nuts on the underneath side. Usually a combination approach is used, drill & tap for bonnet and drill all the way through and use nuts to attach the bonnet scoop.

As a general guide the top rivet on the bonnet should be even with the front rivet on each side of the bonnet scoop.


15-1-15 Pattern –Used on CSX 3020, etc
(one dead centre, 15 rivets up each side edge)
AC Cobra
  • Rivets are positioned 2” in from the front/side edges of the bonnet.
  • First rivet is dead centre of the bonnet, mark and measure 2” in from the front edge of the bonnet and use the centre line to position first rivet.
  • Measure 2” from the centre line in both the left and right directions and 2” in from the edge of the bonnet. 5 rivets on each side of the centre rivet, total of 11 rivets across the front of the bonnet. 
  • Measure and mark 10 rivets up the side of the bonnet, again 2” from the bonnet edge, however the spacing between rivets is 1 ¾”
  • There is a total of 31 rivets around the outside edge of the bonnet (see diagram).
  • The bonnet scoop is positioned 2” back from the bonnet edge.  Measure and mark the bonnet scoop starting with the centre rear rivet. Continue to measure and mark out 15 rivets up each side of the scoop. There will be 31 rivets in total. Spacing between rivets is approx 2”. The final rivet at the front of the bonnet scoop is ½” up from the front edge of the flange. Rivets are positioned dead centre of the bonnet scoop flange, your will need to measure your own scoop as flange size varies according to cobra models.


12-1-12 Pattern –Used on CSX 3042, CSX 3032, etc
(one dead centre, 12 rivets up each side edge)
AC Cobra
  • First rivet is dead centre of the bonnet, mark and measure 2” in from the front edge of the bonnet and use the centre line to position first rivet.
  • Measure from the centre line in both the left and right directions (allowing for the end rivet to be positioned 2” in from the side of the bonnet).  Divide this number evenly into 4 (4 rivet each side of the centre rivet). Measure and mark these rivet holes.  4 rivets on each side of the centre rivet, total of 9 rivets across the front of the bonnet. 
  • Measure and mark 8 rivets up the side of the bonnet, 1 ½” from the bonnet edge, spacing between rivets is 2 ¼”.
  • There are a total of 25 rivets around the outside edge of the bonnet (see diagram).
  • The bonnet scoop is positioned 2” back from the bonnet edge.  Measure and mark the bonnet scoop starting with the centre rear rivet.
    (11-1-11 pattern: continue to measure and mark out 11 rivets up each side of the scoop. There will be 23 rivets in total. Spacing between rivets is approx 2.5”.)  
    (13-1-13pattern: continue to measure and mark out 13 rivets up each side of the scoop. There will be 27 rivets in total. Spacing between rivets is approx 2.1”.)
    Rivets are positioned dead centre of the bonnet scoop flange, your will need to measure your own scoop as flange size varies according to cobra models.


8-0-8 Pattern – As used by ERA, etc
(none dead centre, 8 rivets up each side edge)
AC Cobra
  • Rivets are positioned 2” in from the front/side edges of the bonnet.
  • Start from the middle of the front edge of the bonnet, measure 2” from the centre line in both the left and right directions and 2” in from the edge of the bonnet. Mark and measure the next rivet according to the diagram attached.  A total of 16 rivets around each side of the outside edge of the bonnet, with a total of 32 rivets.
  • The bonnet scoop is positioned 2.5” back from the bonnet edge.  Measure and mark the bonnet scoop starting with the centre rear rivet. Continue to measure and mark out 13 rivets up each side of the scoop. There will be 27 rivets in total. Spacing between rivets is approx 2.1”. Rivets are positioned dead centre of the bonnet scoop flange, your will need to measure your own scoop as flange size varies according to cobra models.


Drilling Bonnet Scoop Flange Rivets
  • Before painting your car measure and mark the desired location of all rivets around the scoop, the number of rivets will depend on the rivet design you choose to use.  (See 3 options above.)
  • Put first rivet in centre of rear of scoop, measure and mark drilling holes for the desired number of rivets up each side of the scoop depending on preferred design. 
  • Drill holes in bonnet scoop flange.  Make sure the bonnet scoop is NOT on the bonnet/car at time of drilling.
  • Reposition the bonnet scoop on the bonnet.
  • Using the pre-drilled holes in the bonnet scoop flange as your pattern, drill your first hole on one side of the bonnet scoop and bolt in place to locate for further drilling.  Repeat the drilling process for all of the rivet holes in your bonnet scoop.  You may wish to bolt every 4th or 5th hole to hold the bonnet scoop still as you drill more holes. 
  • Measure and mark the desired location of rivets around the outside edge of the bonnet, again the number of rivets will depend on the design you have chosen to use.  (See options below.)
  • It is common to have your paint shop drill out all holes for the rivets once the final coat of primer has been applied to your car.  Don’t forget the holes will need to be re-drilled after the final coat of paint.
  • When the paint has had time to fully cure install your rivets around the bonnet scoop and the bonnet perimeter (generally aluminium pop rivets are used).
  • To avoid panel distortion & cracking paint, only use blind rivets with aluminum mandrels or Button head cap screws.

Source:
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