Skin screws coming loose.

[Mike S]

This forum is awesome. I've learned so much and got so much inspiration from you all. Here's a question for the engineers in here.

Charmac builds their Stealth line of trailers with "S" shaped channel steal studs and aluminum skin with a strip of butyl tape between the metal studs and the exterior skin. They say the butyl helps with water resistance. They use the #2 square head self driving screws to attach the skin.

I drive my trailer about 300 miles per week over state roads, some of them bumpy. In the last 6 months, I've put probably 7-10K miles on the trailer. I've noticed that the self drilling screws on my skin are backing out. I can, of course, tighten them back up as needed. But due to the nature of the aluminum and the relatively thin steal studs, I forsee this being a problem in the long term. The screws will get looser and looser every time I tighten them.

So I called Charmac to see what they recommend I do. They gave me the answer which I kind of expected; try blue loctite. However, I'm a little concerned about using blue loctite for this application. I think loctite is meant for situations where there's a lot of screw-thread to substrate contact (that is, something like threading a lug nut onto a wheel, or threading a nut on an engine bolt). In this application, there is very little exposed screw thread.

1) has anyone here experienced this?
2) what product would you suggest that I try on my screws? I was thinking maybe one something like a construction adhesive, or a polyurethane glue like Gorilla glue. Ideas?

Thanks!

[MtnDon]

I've not had any issues with this so far.

You could always try the red loctite. When used on threaded bolts and nuts it is almost impossible to loosen. And FYI there is also green loctite that can be applied after the fasteners have been assembled. Very very thin, low viscosity, it wicks in under screw / bolt heads and all. Not quite as tough as blue though.


construction adhesive, or a polyurethane glue ..... would work, but isn't that going to be uber-messy if used from the exterior side. I could see it being a help id applied to the threaded portion that sticks through on the inside though.

[hankaye]

Mike S, Howdy;

Loctite Red ... used to use it on H-3 and H-60 Helicopters when I worked on them (it was specified in the maint. manuals).
Skins were 0.030" regular #2 Phillips screws ... great stuff. Those helicopters vibrate a lot more than most folks think...

hank

[chiefb711]

Mike S, Howdy;

Loctite Red ... used to use it on H-3 and H-60 Helicopters when I worked on them (it was specified in the maint. manuals).
Skins were 0.030" regular #2 Phillips screws ... great stuff. Those helicopters vibrate a lot more than most folks think...

hank

+1

Loctite Red is amazing!

[Mike S]

I've not had any issues with this so far.

You could always try the red loctite. When used on threaded bolts and nuts it is almost impossible to loosen. And FYI there is also green loctite that can be applied after the fasteners have been assembled. Very very thin, low viscosity, it wicks in under screw / bolt heads and all. Not quite as tough as blue though.


construction adhesive, or a polyurethane glue ..... would work, but isn't that going to be uber-messy if used from the exterior side. I could see it being a help id applied to the threaded portion that sticks through on the inside though.

Thanks MtnDon. uber-messy is right. And I've got I don't know how many screws to potentially create a mess. Since I've already got most of my insulation up, gluing the screws from the inside isn't an easy option. Red loctite seems to be the consensus here.

[Mike S]

Mike S, Howdy;

Loctite Red ... used to use it on H-3 and H-60 Helicopters when I worked on them (it was specified in the maint. manuals).
Skins were 0.030" regular #2 Phillips screws ... great stuff. Those helicopters vibrate a lot more than most folks think...

hank

Okay, I'm going to get the red stuff and try it. Does it dry hard or is it soft?

[chiefb711]

Okay, I'm going to get the red stuff and try it. Does it dry hard or is it soft?

It dries hard. It's almost an epoxy. Here is the info sheet:

http://www.loctiteproducts.com/tds/T_LKR_RED_tds.pdf

[lm248]

I had a similar issue on my dirt bike,,
The same screws would loosen up over time, and then fall out if I didnt catch them in time.
So I took the offending screws out and added a dab of low odor silicon caulk.
They will come out when I need them to.
But they dont back out on there own anymore.

Les

[Mike S]

I had a similar issue on my dirt bike,,
The same screws would loosen up over time, and then fall out if I didnt catch them in time.
So I took the offending screws out and added a dab of low odor silicon caulk.
They will come out when I need them to.
But they dont back out on there own anymore.

Les

I was considering something like caulk. Did it make a mess at the screw head?

[lm248]

[/quote]
I was considering something like caulk. Did it make a mess at the screw head?[/quote]

If you fill the hole full then yes it would ooze out,
I just put a dab on the threads,
Then tighten down,,,
The thing I like about caulk, is it doesnt harden.
Then if you have to pull the screw out there's no residue left in the hole.
I also like it because it cuts down on the dissimilar metal issue.
( which is important in a motorcycle application )
However having said all that I don't know if I would use caulk with a fastener that had to be torqued.
I'm not saying it wouldn't work i've just never used it that way....

Les

[Mike S]

Dissimilar metals...hmm. This has got me thinking; Charmac uses butyl putty between the outer aluminum skin and the steal studs. I didn't even think about the dissimilar metal issue, but maybe that's a benefit to the putty. However a disadvantage of the putty is that it will prevent any thread compound from contacting the steal studs. So whatever compound I use will have to do it's thing at the aluminum skin to screw head contact point.

[Gonefishin]

I've had a bunch of skin screws work out of my Haulmark after tens of thousands of miles. I've been screwing them back in with some marine silicone. After tightening, I just wipe away the excess, and they never come out again. No leaks either. I do the same thing with screws on boats. 3M 5200 is the heavy duty chit, but may never come out! A simpler clear or white silicone works fine too, and makes unscrewing easier if you ever had to do that. I never have. There's also a GE "aluminum caulk" I had to use, and it also worked great, and is my first choice now. Here it is. http://www.amazon.com/gp/product/B000BP7Z48/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

[walkrdg]

Gonefishin...
Thank you for that. I've bookmarked that caulk.
Dave

[sbshaver]

Is bolting feasible?

[Mike S]

Bolting is not really feasible because I've already got my insulation in and walls re-installed. Similarly I've considered aircraft structural rivets, but just like bolts, you need access to both sides to put those in. I suppose I could tear apart the work I've already done but I'd rather not.

I've been using Geocel Proflex RV Sealant on other areas of the trailer and have found it to be an excellent product. I wonder if it would work well for my screws, like caulk? http://www.geocelusa.com/product/all-rv-aftermarket/pro-flex-rva-flexible-sealant-detail.html