Rivnut vs Plusnut

[David T]

The root of the problem with the riv-nuts is the exposed length of the threaded fastener protruding out of the "back" of the riv-nut. It corrodes and when you try to remove the screw and you get to the corroded threads it jams up. In trying to force the screw, it binds up inside the riv-nut and because the force to rotate the riv-nut in the fiberglass is less than what is required to loosen the screw, the riv-nut rotates. Once it rotates you can no longer remove the screw. Worse still, the hole in the fiberglass gets enlarged so you cannot repair using a riv-nut of the same size, it requires a riv-nut with a larger diameter. Riv-nuts and similar fasteners operate only over a very small grip length and hole size. The ultimate repair would be a nut plate. Basically a rectangular plate with a hole in each end for a rivet and a central hole that is threaded. A very good replacement is a "jack-nut" which is like a sheet rock toggle bolt. Look them up over at Mr G's Hardware. They are used a lot in later Lotus's. They have a long grip length and are not as sensitive to the hole diameter.

[nkemp]

... I have been thinking of having a stainless "ring" fabricated that would have nuts pressed into the backside of the ring. I imagine that the ring could be installed through the opening and held in place with adhesive to the backside of the opening. Then, the panel would be re-attached with new screws.

I'm not quite sure what you are thinking of doing ... but if you can get to the backside, there are a number of options. Maybe "T Nuts" would work. Tighten the first time tight enough to set the "points" or "barbs". I'd epoxy them in place. Usually the flange is put to the back side but I used them to hold the battery compartment door. Because I couldn't get to the back side, I epoxied them to the front of the wood. Then I use thumbscrews to hold the battery panel in place. I suppose if I tightened too hard it might pull off the board. If so, redo it. To keep epoxy out of the threads, put oil or grease or wax or similar on the threads before epoxying.

If you don't want the "points" then grind them off. I believe there is something similar to T-bolts but bigger flanges and designed to be glued. Kinda like the studs in the bumpers except nuts instead of bolts

[nkemp]

Unless you're talking about digging into the fiberglass, which I can see.

Basically that is it. It all depends on how well the cross forms and how much the cross grabs the fiberglass on the backside. If it was to squeeze tight against the fiberglass, then it should hold better than a Rivnut in fiberglass. But it does beg the question of how consistent the plus forms and grabs. If the plus forms in such a way that it is not in contact with the fiberglass then you may have a bigger problem than what you started with.

Rivnuts in metal makes sense. Rivnuts in fiberglass does not make sense especially any application where the bolt needs to be removed on occasion. It is a matter of time before the Rivnut spins ... and the mechanic cusses. Kinda like those plastic wall anchors in drywall. Sorta OK to hold a thermostat, not OK for the toilet paper holder. Sooner or later you end up with a bigger hole and spinning anchor.

[Shep]

Sooner or later you end up with a bigger hole and spinning anchor.

And at least in my house, a new cat toy.

Rivnuts on metal "work", but they are still annoying as hell, and still strip just as easily as fiberglass, if not more easily due to the normally decreased thickness (and "give") of sheet metal vs. fiberglass. Welding nuts into the backside is a much sturdier approach I've seen on some of my cars. They are often painted over in this process.

[Bitsyncmaster]

I have the same issues in the luggage compartment. I suppose the screws seized in the rivnuts, so the rivnuts spun and pulled out of the fiberglass and blew out the holes. So, someone applied a heavy bead of RTV on the panel and used larger sheet metal screws to re-attach the panel.
Short of patching the fiberglass at each hole, drilling new holes, and inserting new rivuts or similar, I have been thinking of having a stainless "ring" fabricated that would have nuts pressed into the backside of the ring. I imagine that the ring could be installed through the opening and held in place with adhesive to the backside of the opening. Then, the panel would be re-attached with new screws.
Dave, is what I have described what you are thinking?

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That is what I was thinking. That thought crosses my mind every time I install the rear stop light fixtures. Actually they did use that idea on the rear license plate light.

[nkemp]

Is something like this what you are thinking of?
8IN_3675.jpg5-16-t-nut-a89.jpgT-nut.jpg

Obviously these are a lot easier to install if you can get to the back side. I suppose you could slot the hole, insert with a string attached and pull it back towards the hole. Epoxy would secure it. But that would not be easy!

The one on the right can be used on the front side using a couple small screws to hold to the fiberglass .., and applications without a lot of pull load.

I used the middle one on the front side of the plywood panel for the battery cover. It works great. And the thumb screws make removing the cover a lot easier/quicker.

[nkemp]

These might be a great option ... Mag Daddy Blind Nuts: http://magdaddyusa.com/products/all-...ez-blind-nuts/

The downside is the need for a 1/2 inch hole which may not look right in all applications.

https://www.youtube.com/watch?v=sKwtJYssUQo

[Shep]

Is something like this what you are thinking of?

[pics]

With the first guy, you simply put an other layer of fiberglass on top of it ("patch" it) to permanently affix. The shape alone prevents spin-outs. They often already appear similar to that, just built into the metal bodywork of cars, I see a lot of it in trunk and engine bay areas in late-model cars that need good grounding points. Sometimes you'll see it in the B-pillar if you can access the seat belt mechanism too. It's a robust solution that doesn't fail often in the right application. Middle guy is typically wood-only due to the depth of how much it needs to dig and also the directional strength of the grain.

I would also be interested to know what they use on carbon fiber vehicles. Formula One and later lambos might be a good indication here.

EDIT: Also, just to be clear, I am talking about the "ultimate" approach being to add these as part of the manufacturing process, not as part of a generic repair job. It could be a huge undertaking to make the swap once the car is assembled for sure.