question about rivnuts

[Farrar Hudkins]

For those with experience installing riv-nuts... a question.

To attach my fuel pump bracket, I am planning to install a riv-nut in the fiberglass body in front of the HVAC box. (Or, if you're inside the car looking forward, at the *back* of the HVAC box.) How thick is the body material there? There are different rivnuts to buy for different thicknesses of material, and McMaster-Carr charges dearly for shipping. Also, they sell different rivnuts for installation in plastic and composite materials. Since the body is GRP, should I buy the rivnuts designed for use in plastic (which look like jacknuts), or go with the standard solid-tube type?

Also, since I am essentially mounting a fastener into the back of the HVAC system, should I use a closed-end rivnut to prevent leakage into and out of the HVAC system there?

Sorry if these questions are unclear. I'm on cold medicine and fairly groggy at the moment, but I've been inside all day and going a bit stir crazy need something to think about.

Thanks,
Farrar

[Bill Robertson]

None of the HVAC components actually touch the firewall.

Lower portion of the firewall is surprisingly thick. There's a layer of foam sandwiched between fiberglass "crusts." Pull your lower speedometer cable out and you'll see what I'm talking about. That foam extends to the passenger side -- I drill through it next to the evaporator box when running my ground buses. How high up it goes I do not know.

Bill.

[Farrar Hudkins]

Thanks, Bill. That gives me a good starting point. I'm going to measure the fuel pump bracket and see what size bolt/washer I need, then find an appropriate rivnut for that thick material. McMaster carries everything from a fraction of a millimeter up to over an inch, I think.

Farrar

[Bill Robertson]

I would bury the rivnut in the foam rather than trying to go all the way through. I'm pretty sure that's how the trunk latch rivnuts are mounted. Outer layer of fiberglass is probably 1/8" or so.

Bill.

[Farrar Hudkins]

That seems to be the way the rocker panel rivnuts are attached, as well. Kenny in Alabama recently had his rocker panels off and talked about the fasteners going onto a kind of foam beyond.

Speaking of which, I wonder if well-nuts would work in attaching rocker panels and other externally-mounted bits for protection against moisture intrusion. I imagine they'd be a maintenance item, since the rubber would eventually degrade, but I wonder how long they'd last. I'm only thinking of this because Kenny used all stainless hardware for his rocker panels, but I'd want black since it's less noticeable.

Boy oh boy, looking through McMaster's catalogue gives me all sorts of strange ideas. I could probably spend all my money with them.

Farrar