Wednesday, November 18, 2015

Bonnet gas struts

I have decided to fit adjustable gas struts to the bonnet, rather than the standard GD opener, even though I have been warned off by GD. I have seen a number of Cobra type cars with them installed for both the bonnet and boot, including GD, AK and Dax, but I have not yet decided what to do with the boot.
Simon Smith's AK with gas struts
If the pressure exerted is too great, the GRP can become distorted. So I knew that I needed adjustable gas struts and brackets that would spread the load to avoid any distortion. After contacting SGS Engineering in Derby, I was convinced that I could install gas struts successfully, using my own brackets.

Using the bonnet stay purchased from GD, I calculated the length of struts to order. I decided that 8 mm diameter was adequate - this is the rod diameter. I then worked out the stroke and the extended length that I required, which was around 220 mm and 470 mm respectively. The nearest gas strut stroke that SGS offered in their NitroLift range was a 200 mm stroke with an extended length of 450 mm (measured to the shoulder of the cylinder) - part number GSV8-200.

The end fixings ordered were 10 mm ball stud type and this adds 25 mm to the end of the centre of the fixing, with an M6 male fitting. This will give an extended length for the strut of 500 mm (450 + 25 +25) and a stroke of 225 mm (200 + 25) which should be ok. The total cost was around £45, plus the brackets etc, so say £50.

To keep the bonnet stays open, with the bonnet lifted, I also ordered a safety lock for each strut. These did not fit - see later!

Thanks to Rob here for the guidance - see the link to his blog to the right of this article.

Lower fixing

To locate the strut to the inner wing, I made a pair of brackets from 25 mm angle 3 mm aluminium, with three 6 mm holes (one in the centre for the strut location/pivot point). The brackets were 250 mm long and fitted up behind the lip of the engine bay. One needed a small amount of filing as the return was slightly smaller.
Bracket with three 6 mm holes
The front of the bracket is located above the suspension cut out - just make sure that the central hole (the pivot) is at the same point on each side). With the pivot point here the strut should be upright when the bonnet is open. Before fitting the bracket, the position of the three holes were marked on the GRP and opened out to 6 mm.
Hole positions for the bracket
Each bracket was fixed in place with two M6 button head screws and nyloc nuts, the pivot from the gas strut and some No More Nails. Nut lock was applied to the pivot nut.
Bracket fixed in place
Upper (bonnet) fixing

The cylinder of the strut was positioned at the end farthest away from the body fixing point (nearest to the windscreen). The other end was fitted to the pivot point on the body. I then compressed the gas strut (after releasing the pressure for about 15 seconds [apparently this reduces the pressure from 700 N to around 250 N!] - but check your own struts for this) and marked the pivot position on some masking tape attached to the wing. The distance was 300 mm from the centre of the body pivot. I then transferred this to some masking tape on the bonnet.
Pivot position marked on wing and bonnet
For the top brackets, the ones that fix to the bonnet, I again used some more aluminium angle (I was going to use 'T' section to keep the load in the centre, but the fixings would not have been ideal on the bonnet ribs, as they are relatively narrow). I made the brackets 200 mm long and shaped them to leave a fixing lug at the centre for the ball stud pivot.
Off-side bracket
Four 6 mm holes were drilled in each bracket, two either side of the pivot. For the pivot point another 6 mm hole was drilled - 12-14 mm in from the 90 degree return of the angle (this is to avoid the strut fouling the capheads).  The brackets were then used to mark the holes to drill in the underside of the bonnet rib  for 6 mm rivnuts. The holes were drilled, the rivnuts inserted and then the brackets were secured to the bonnet with button head bolts.
M6 rivnuts in place
Once the strut had been fitted, the pressure was checked. The strut was adjusted by opening the hex adjuster for about one second at a time (this should be done the same amount on each side until the struts exerted just enough pressure to hold the bonnet open).
Strut from inside the engine bay
Strut from outside the car
Finally, I tried to fit the SGS locking tubes. These are designed to keep the bonnet open, even in winds. However, I found that the tube was too wide and fouled the body, so couldn't be used.
Locking tube fouled the lower mounting point when the bonnet was lowered
Now I just need to do the other side!

6 comments:

Andrew Sherratt said...

Can you put a spacer on the body mounting of the strut so it clears the body with the locking tube fitted?

Dale said...

Hi Andy Thanks for your suggestion. How are you? The ball pivot fixing is not long enough to add a spacer, but I have asked if they have a longer one that I could space out without exerting too much pressure at this point. Dale

Andrew Sherratt said...

I'm well thanks, I expected you would have thought of this but it was the only suggestion I could think of! Looking forward to seeing the completed car.

Dale said...

Great to have your comments or suggestions. Very useful. When you are at the coal face, it can be difficult to see anything but black!

Andrew Sherratt said...

Would something like this work - http://jksmfg.com/i-10079662-bolt-extension.html

Dale said...

Could be ok. Thanks. I want to keep the fitting as short as poss. to avoid too much leverage on pivot. Will see what SGS say. A nut on a longer threaded ball fixing may do the trick