Dzus fastener help

nfharris · Post by **nfharris** » Mon Jun 20, 2011 12:54 am

I am wanting to change the dzus fasteners on my cowling. Can someone please explain how I remove the old grommits and install the new ones? Do I need the (very expensive) installation tool?

Any help much appreciated.

Brian Hope · Post by **Brian Hope** » Mon Jun 20, 2011 6:37 am

Have to say I'm not a fan of Dzus fasteners, mainly because you do need a rather expensive tool to fit them. Hopefully somebody will come back with a quick fix and insexpensive method. If not you may wish to consider using Camlocs, which are much easier to install. That will unfortunately mean re-glassing the existing cowling holes as they are rather smaller in diameter.

macconnacher · Post by **macconnacher** » Mon Jun 20, 2011 1:08 pm

As Brian says the tool makes it expensive if you need to do it. I have come across Dzus fastners with a built in small Al backing plate that you can glass into the cowling. I am assuming that we are talking about a glass fibre cowling as on a Jodel.

nfharris · Post by **nfharris** » Mon Jun 20, 2011 4:53 pm

Many thanks gents.

It is a fibreglass cowl but for an Emeraude; the dzus fasteners though are part in the metal latch. If I make my peace with buying the tool could someone please explain how it works? I suspect that removing the old grommets may be more difficult. Does anyhow have any experience of removing them?

Much appreciated

Richard Mole · Post by **Richard Mole** » Sun Jun 26, 2011 6:35 pm

I made a very simple tool 20 years ago that seems to work OK to this day on the winged Dzus fasteners. The 'tool' is just a pair of small steel cylinders machined as follows.

One end of the first steel cylinder, about the same diameter as the wings of the stud, has a cup and a slot machined on one end. THis part of the 'tool' just allows the winged Dzus fastener stud to nestle in.

This combo is offered up to the cowling once the collar has been loosely pressed in place from the outside (I usually put a dab of body filler with hardener between the two so that no gaps remain after fitting).

The second part of the 'tool' is an even simpler cylinder with an axial drilling to match the Dzus stud. The drilling has a very small radius where it exits, at the end that will abutt the collar (ie on the inside of the cowl).

A G clamp presses the two cylinders together. The collar being very soft aluminium simply folds back against the inner face of the cowl and as it does so its internal diameter also closes up. This closing up prevents the Dzus fastener falling out. One final grunt on the G clamp and it is loostened and removed along with the cylinders and hey presto!

With the larger size of Dzus fasteners this scheme may need an initial operation to kick start the collar deformation. So you put the second cylinder with the axial drilling on the OUTSIDE of the collar when it is inserted into the cowl with its dab of filler paste but BEFORE you install the Dzus stud. A third part of the 'tool' is simply a shouldered stud with stud diameter equal to the original collar id. The shoulder is angled at say 45 degs (any old angle should work OK). The third part of the tool is inserted from the inside of the cowl. The trusty G clamp then presses the shoulder against the protruding collar to start it spreading out. Only press it lightly as all you want to achieve is that the collar has learnt that it must spread out evenly under pressure. Then remove the tool and quickly do as described above.

Warning: if the spreading pressure is too extreme then you will not be able to get the tool out without scrapping tthe collar (very cheap and a doddle to cut or file away)

There is absolutely no need to buy an expensive tool. If you want to fit hundreds then I guess you could get the machined cylinders hardened. But a decent bilt of mild steel should last you a lifetime.

Tip: order two or three times as many collars as you studs and have spares to last teh life of the aircraft because collars are soft aluminium and they don't last for ever.

Richard Mole · Post by **Richard Mole** » Sun Jun 26, 2011 9:56 pm

PS. You should only need to remove a grommet (what I called a collar) if it is damaged. When it is damaged you will probably find that you can cut it away with a Stanley knife plus some brute strength, starting at the worn area. Failing that, a combination of a needle file and a short length of junior hack saw blade (without the spigots) will do the job. It looks much tougher material than it actually is!

PPS Buy a selction of springs because they are cheap enough and you may well find that due to varying cowl thickness (and the like) you will need a deeper and also a shallower spring than the type that best suits the majority of the fasteners.

PPPS !! if you line the cowl with the very thin sticky backed silver foil tape you will protect the material from oil seepage, lower the temperature of the cowl material especially near the exhaust pipes, and find that a quick wipe with a rag is an easy way to keep the inside surface pretty spotless (and it weighs nothing worth mentioning)

nfharris · Post by **nfharris** » Tue Jun 28, 2011 12:50 am

That's fantastic thanks very much Richard.