Dzus fasteners

Jim Rosenthal

Supporter
We've gotten to the point where I have to install Dzus fasteners in the nostril panel and front clip. There seem to be four openings for them; two that help hold down the front bodywork, which are located up by the base of the windscreen, and four that hold the nostril panel into the front bodywork. So here are a few questions from someone (me) who understands the basics of how these things work (quarter-turn spiral/spring fasteners) but doesn't have very much practical experience with them at all.

1) it looks to me that if the Dzus fastener holds a fiberglass panel down onto a steel one, in compression, there ought to be some kind of cushion under the fiberglass panel, otherwise the strain of being held down onto the (relatively inflexible) steel panel will eventually crack the fiberglass. True or not true?

2) also, it looks like there ought to be some kind of backing arrangement where the Dzus fastener is riveted to the fiberglass panel(s), otherwise the rivets will tear or pull through the fiberglass. True or not true? I figured some kind of aluminum plate ought to be under there to spread the load out. Any comments?

3) should Dzus fasteners be bolted or riveted to the panel that they are installed on? (if riveted, we'll have to size everything and then get all the paintwork done first, since once they're riveted on, they stay there until you drill the rivet out, or break it, either of which will end up requiring the paint be touched up.

There are probably a few things I haven't thought of, which if anyone knows of them, please let me know. I'd rather hear about my mistakes BEFORE I make them,not after. There are a variety of these kinds of locking systems, but since Dzus fasteners are what were on the original car, the choice is made simple. Too bad they don't make them with those little handles that you can see on the original cars. Robert Ashe brazes those on and then replates the whole assembly. Guess who isn't going to do all that?
 
Jim,

I have a SPF MKII, so it may not apply, but mine are riveted. Looking at them, I would have done it a little different and i am considering removing and reinstalling them. I never rivet through fiberglass without a backing rivet washer or backing plate to spread the stress.

Here is one example of how to attach DZUS to fiberglass. Note the backing plate. This is more how I would do it. If not the backing plate at least rivet washers.


Kinetic Vehicles

For authenticity, you need someone else's knowledge.
 

Jim Rosenthal

Supporter
Very useful. I think that I can find enough parts in Pegasus to figure out how to do this and not make a hash of it. Any other advice? don't hesitate...
 

Malcolm

Supporter
On my GTD I have used the Dzus fasteners without issue. I have riveted them on and used backing washers, it does make sense to fit these if the space permits. Mine have been on my car for 18 years now, does that constitute a long term test? :) I have not noticed any cracking of the paint around them either. As to fitting prior to painting, just drill the correct sized holes in the bare fibre glass and then when it gets painted the hole should be a bit small. Re drill it to the correct size again and then final fit. That way the rivet is gripping the fibre glass and not a painted surface which could let go and crumble under any stresses. I have seen on other cars nice looking counter sunk headed bolts with nyloc nuts holding fasteners on and that would work very well.

I have carried out two very non scientific crash tests with my car, one back in 1993 with the outside tyre wall at Madgewick at Goodwood and once in 2002 at Martini at Wiscombe Hill Climb with an earth bank. Both frontal impacts. One needed a new front clip and the other a new windscreen after the front clip got pushed through the windscreen. At Goodwood, all Dzus clips held up well which is why the front clip needed replacing as it did not come backwards so the fibreglass just tore up. As an aside the side latch clips both gave up in this incident. At Wiscombe which was a slower impact, again the dzus fasteners held up but the wires underneath them both bent out of shape so releasing the front clip to push back and up through the base of the windsceen. In both cases the nostril dzus fasteners held up and did not fail at all.

So I think backing washers will work just fine but there are prettier ways of achieving the same goal.
 

Chris Duncan

Supporter
For the nostril you can bolt the dzus fasteners if you don't want to rivet. On mine I used 6-32 internal hex stainless and tapped threads in the fiberglass, there's very little force on these fasteners. The only issue is where the wire part of the fastener goes on the front clip. Should it be on top of the clip or underneath it? If on top then it has less holding strength because it can be relatively easily pulled out. If you look at the configuration of the wire it's structurally weak in that it's just coiled on each end, the coils can unwind under force. If underneath the clip it's much stronger because the wire would have to be pulled through the fiberglass to fail.

It all depends on whether you have a full depth nostril. There have been failures due to non-aero (partial depth) nostils taking flight at speed due to the wire dzus part being on top of the clip and ripping out. The non-aero clip causes the front clip to build pressure which pushes the nostil up and out. The only problem with putting the dzus wire underneath is standard zues fasteners aren't long enough to reach.

The other dzus on the front clip, by the lower front edge of the windshield has issues also. While the dzus is more prevalent you can use a captive hood pin for more secure retention. You can also add a layer of fiberlass underneath at the location if cracking is a concern. About a 4" diameter patch one or two layers thick.

Stainless Hood Pins with Captive Clips
 
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Malcolm

Supporter
On the nostril dzus fasteners, for the front two you need to check clearance with your radiator. The fixings on the clip part, whatever you chose, pass very close to the radiator on a GTD replica so if you have the wire underneath as suggested, check your clearances for when you open the front clip up. Other replica makes may not have this issue to contend with.
 
Jim, another simple solution we have used in areas of concern is to manufacture the centre Dzus pin as a thread rather than a twist cam lock. A nut on winged holders are available or again can be made in house, and this provides a very position lock for panels whilst retaining the same visual image of the Dzus externally. The only downside is the slightly longer time it takes to unscrew the fastner rather than quarter turn it. Frank
 

Terry Oxandale

Skinny Man
1) it looks to me that if the Dzus fastener holds a fiberglass panel down onto a steel one, in compression, there ought to be some kind of cushion under the fiberglass panel, otherwise the strain of being held down onto the (relatively inflexible) steel panel will eventually crack the fiberglass. True or not true?

My experence has been "false". With that said, the steel must be parallel and conforming to the shape of the overlying panel in the immediate area of the fastener. In fact, any cushion will cause the fiberglass to distort and crack if the cushion is larger than the Dzus fasteners steel support attached to the fiberglass panel (which is pretty small).

2) also, it looks like there ought to be some kind of backing arrangement where the Dzus fastener is riveted to the fiberglass panel(s), otherwise the rivets will tear or pull through the fiberglass. True or not true? I figured some kind of aluminum plate ought to be under there to spread the load out. Any comments?

I've always used aluminum washers with the rivets. Unfortunately, they take up a bit more area than the anvil of the rivet, so this must be dealt with on the supporting steel holding the spring in place. Remember though, these fasteners act in a compression mode, so in reality, no rivet is required in order for them to work properly. The rivets really only hold the fastener in place on your fiberglass panel once the fastener is released.

3) should Dzus fasteners be bolted or riveted to the panel that they are installed on? (if riveted, we'll have to size everything and then get all the paintwork done first, since once they're riveted on, they stay there until you drill the rivet out, or break it, either of which will end up requiring the paint be touched up.

I installed mine for the mock-assembly stage, then drilled them out and removed them for the painting stage, and then reinstalled them for the final assembly.

There are probably a few things I haven't thought of, which if anyone knows of them, please let me know. I'd rather hear about my mistakes BEFORE I make them,not after. There are a variety of these kinds of locking systems, but since Dzus fasteners are what were on the original car, the choice is made simple. Too bad they don't make them with those little handles that you can see on the original cars. Robert Ashe brazes those on and then replates the whole assembly. Guess who isn't going to do all that?

My biggest problem with using these fasteners is getting the correctly sized Dzus for the thickness of the panels held together. Too short or long, and you've got to distort the spring, which is no problem for small adjustments (stretching the spring is a lot easier than compressing the spring), but the larger adjustments really need the correct length of fastener in the first place.
 
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Jim Rosenthal

Supporter
All of this is very much appreciated. I am going back to the shop this afternoon and looking all this over again and taking some measurements. Thanks to all and any additional comments are welcome as well.
 
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