Bonnet strutt modification

[Tintin]

The struts on my 1996 celebration are the original and now weak and I am thinking of replacement. In the open position as fitted to the bonnet the standard struts extend to 500mm (centre to centre of ball pivots) which gives very low headroom for working under the bonnet. I fiddled about today and reckon the bonnet will take 590mm centre to centre which gives a massive improvement for head clearance and working access. At this extended distance, the bottom of the grille just brushes the top of the bumper plastic finisher but without leaving a mark; the hinges also just clear the finisher. The bonnet will also then open to a wider angle (55 degrees approx. as opposed to 40/45 degrees) and thus the force required to hold it in the open position should be less.

I can get struts specially made to achieve 590mm open, 335mm closed, 8mm dia rod, 19mm dia tube, 10mm ball sockets and a power of 210 Newtons (I think this is the power of the original struts) but at a cost!!!

A similar modification is described on the Jag Lovers web site.

Before I launch into this does anyone else have experience of fitting modified bonnet struts?

PS I have considered using a bit of old stick as a bonnet prop, but its not quite "Jaguar" is it?!

Robbie

[Brakebuster]

won't the mounting point on the inner wing need to be moved to take the longer strut ( when closed )

to be honest, in 14 years of ownership , i have got used to the amount the bonnet opens allowing me to work , just one of those things


BB

[steve_m]

It depends on the bit of old stick really.
If it has provenance i.e. ex baton from the Sergeant Major of the 14th Foot and Mouth, last used in the Zulu difficulties then it will probably be fine.

[Brakebuster]

It depends on the bit of old stick really.
If it has provenance i.e. ex baton from the Sergeant Major of the 14th Foot and Mouth, last used in the Zulu difficulties then it will probably be fine.

or a cut down broom stick ,

BB

[Tintin]

I did ask my wife if I could borrow her broomstick to hold up the bonnet and it was suggested that I might like it wrapped around my head instead!

Ergo - I will do the modification, save my cranium, and let you all know how I get on!!

Robbie

[Brakebuster]

how and where will the new mounting points be installed ?

BB

[Tintin]

I intend to retain the existing points and ball pivots. Because the new struts will be the same closed length as the existing, they will fit between the fixings when the bonnet is closed. Because the new struts will have the same rod and tube diameter they should have the same side clearances to the edge of the wing and bonnet when closed and in operation. I cannot see that the additional open length will cause an issue re the position of the pivots/fixings. Am I missing something here you have spotted BB?

[Brakebuster]

i may be wrong

but if the struts are the same closed length , then how can they be longer when open ?

as the two rods ( one inside the other ) will only open to the same length ?

as the existing struts are fully closed up when the bonnet is down ,

just cant see how this can be achieved without extending the strut closed length and therefore the mounting points when closed need to be moved further apart ?

just my thoughts

BB

[Tintin]

Thanks BB and always happy to receive a reality check to my ideas. I have re-measured the strut closed length with bonnet shut and obtained 332mm and 329mm (slightly different per side due to bonnet flexing) measured to centres of ball pivots. SGS can produce a strut with 330mm closed and 590mm open lengths. If the strut cylinder is, say, 290mm long and each fixing socket adds another 15mm x 2 = 30mm that gives a closed length of 320 in all so 332 and 329 will be accommodated. When extended 270mm of piston in the 290 long cylinder will move out (stroke) giving an extended length of 290mm + 30mm + 270mm = 590mm. I have talked this through with SGS engineering - they say it will be "tight" but achievable.

The existing strut cylinders are about 290 long but the pistons move out (stroke) by only 215mm giving the "standard" open length of 505mm approx. The closed length of the struts is 305mm whereas the closed distance between the fixings is 330mm and thus there is unused travel in the existing struts.

SGS have given me a more competitive price for bespoke struts than the other supplier I approached, and at the SGS figure I am content to try it and see.

[Brakebuster]

cool

I get it now,

and for every mm gained at the pivot point , the bonnet opening at the top is exaggerated further

would like to see side on pictures of before and after with the bonnet open if you can

BB

[Tintin]

Even with thorough research I can't be 100% sure it will work until I try it, but if it does I'll do a little write up with photos in case anyone else wants to try it.

Robbie

[Tintin]

I have now done the work and the result is amazing - the bonnet rises and holds open smoothly under strut power and there is much improved clearance, especially at the radiator end. I did the work as follows.

1 Raise bonnet and prop open with temporary support. Remove old struts.
2 With the aid of an assistant continue raising bonnet all the while monitoring clearances at the front. Critical clearances are bottom of grille to bumper, and bonnet hinge cover plates to bumper. When the desired/maximum opening has been reached fit a longer temporary prop to hold the bonnet open at the new position.
3 Measure and record the distance between the centres of the strut mounting points.
4 Lower the bonnet to the original open height and re-fit the original gas struts. Tie a small piece of string tightly around the strut piston rods; close and latch the bonnet and then re-open to the original height. The string will have moved to the position of the cylinder when closed. Measure add together and record the string to mounting and cylinder lengths to get the length of the old strut when closed.
5 Measure and record the piston rod and cylinder diameters and the mounting point details.
6 Order new struts same as existing (the force in Newtons will be stamped on the strut body) except with the new closed and open lengths. My maximum closed length was 330mm which limited the maximum new strut open length to 585mm - only 5mm less than my ideal.

I had my struts made and supplied by SGS Engineering - they were absolutely brilliant (Ashley took a lot of time and trouble to check, double check and get it right with me) - cost not much more than off the shelf units and they arrived the next day. A 10 minute job to fit. Cannot understand why I didn't do this a long time ago! Will upload more photos later today.

Before

After

Better access to front of engine bay

Robbie

[Tintin]

Further photos attached

Grille clearance

Hinge clearance

String helps measurement

[Brakebuster]

great work and seemingly worth the effort

i will say that your original struts seem more limited than mine , ( 1989 coupe )

i will take a side on pic myself and pop it up for comparison , as i feel that i have a similar angle to your now modified struts

the results will be interesting

BB

[davidr]

Robbie - looks good - a really worthwhile mod. I'll have to do it on mine.

BB - the struts on the later cars are different in that they have a self-locking mechanism to keep them up so they don't sag and clock you on the head when they start to lose pressure. It may be that their extended length is different. I'll measure both my cars when I get a chance and report back