Drilling into Fiberglass to Attach Something

[lazabby]

I need to attach something to the wall of the engine bay. This means that I will have to drill into the fiberglass. What kind of screw do you use to attach things? I can't use a bolt since there is no way to attach a nut to it. Do you use some kind of wood-type screw?

[Delorean Industries]

What are you trying to attach?

[stevedmc]

It sounds like either a cruise control unit or a fuel filter mount to me.

[DMCMW Dave]

I need to attach something to the wall of the engine bay. This means that I will have to drill into the fiberglass. What kind of screw do you use to attach things? I can't use a bolt since there is no way to attach a nut to it. Do you use some kind of wood-type screw?

If it's not too heavy a sheet metal screw will work. It's better if you use a rivnut (like everything else on the fiberglass is attached). You can actually get to the back side of most of the fiberglass in the engine bay though - where are you trying to attach something?

[Ron]

Togglebolts are another option:

8630

[lazabby]

I'll attach something next to the battery post by the bulkhead. It won't be heavy.

[dustybarn]

I concur on the Rivnuts:

http://www.aircraftspruce.com/catalog/hapages/rivnuts.php

...depending on how thick the fiberglass is in that area. You'll have to measure the thickness to get Rivnuts with the right grip range.

[Spittybug]

Shannon is attaching a 12V+ bus bar that his friend gave him. Bitsyncmaster just did this I believe.... Dave, how did you attach it? As part of Shannon's EFI conversion we are taking the time to fix a lot of the other things that need addressing in his car. His wiring harness was a little chewed up. Since we are removing so many of the wires with the conversion, I have made him a replacement harness with only the required ones, all neat and tidy within a polyester loom (pics in EFI section once posted). Additionally, he will be getting rid of the ridiculous 12V+ daisy chaining with the triple brown wires like I did. Instead, he will have 4 connections to his nice new bus bar:

Battery +
Main 12V+ car bus post in bulkhead box
Starter
Alternator

All done with nice new red battery cables. Me, I'd use some kind of toggle to ensure that the bar can be drawn nice and tight to the fiberglass and I'd cover over the hole left behind by removing the jumping post.
Shannon, add your general location info to your profile!

[Bitsyncmaster]

I used a "nutplate". That is an aluminum plate that I drilled and tapped. It was tricky getting it in that small existing hole, holding there and getting the two 4-40 machine holding screws installed.

I would just recommend you use #10 sheet metal screws to hold it to the fiberglass. The large sheet metal screws will hold very good. Drill a hole the size of the non-threaded shaft of the screw. You may have to drill a little larger if you can't get them to go in.

[David T]

I don't like using sheet metal screws into fiberglass. They can loosen up from vibration and temperature changes. Much safer to use a machine screw into a rivenut or a nutplate. It is also easier to overtighten a sheet metal screw and strip the hole and now it won't hold at all. Most people treat fiberglass like wood and use sheet metal screws or wood screws. IMHO this is not good especially if you take it apart a few times. Eventually you will strip the hole. In fact, there are few places I would even use a sheet metal screw anywhere on a car.
David Teitelbaum

[lazabby]

I agree that a rivnut would be best. I don't have the tooling so I did go with a sheet metal screw. It's worked just fine.

One thought to keep in mind. The place where the sheet metal screws went in is next to the bulkhead. I contemplated removing the bulkhead to see if it would allow access behind the fiberglass. If so then a bolt could be used with a nut behind the fiberglass. Has anyone removed the bulkhead to see if it does allow access behind the fiberglass?

[Bitsyncmaster]

I agree that a rivnut would be best. I don't have the tooling so I did go with a sheet metal screw. It's worked just fine.

One thought to keep in mind. The place where the sheet metal screws went in is next to the bulkhead. I contemplated removing the bulkhead to see if it would allow access behind the fiberglass. If so then a bolt could be used with a nut behind the fiberglass. Has anyone removed the bulkhead to see if it does allow access behind the fiberglass?

I was thinking about the same thing when I did mine but thought it would be to much work. Let us know if you decide to try this.

Also forgot to suggest, using sheet metal screws into the fiberglass works better if you use a little hand soap on the treads to give it some lubrication.

[lazabby]

I was thinking about the same thing when I did mine but thought it would be to much work. Let us know if you decide to try this.

Also forgot to suggest, using sheet metal screws into the fiberglass works better if you use a little hand soap on the treads to give it some lubrication.

Since I already have the sheetmetal screws in I won't try to remove the bulkhead. But if something happens in the future and the screws get loose and won't tighten or whatever, I'd like to know if I can access the area via going through the bulkhead. Since I've never taken that off, I'm not sure what access it allows.

[dmc6960]

I contemplated removing the bulkhead to see if it would allow access behind the fiberglass. If so then a bolt could be used with a nut behind the fiberglass. Has anyone removed the bulkhead to see if it does allow access behind the fiberglass?

I believe the open access from the inside of the car goes no further than the main harness. The location where the existing 12V post is must be accessed from the rear (remove rear fascia, reach up hole, curse when your arm doesn't quite reach).

[dmc6960]

I have sheet metal screws with large heads holding on my fuel pressure regulator. Its held quite well for 2 years so far.

[DMCMW Dave]

I If so then a bolt could be used with a nut behind the fiberglass. Has anyone removed the bulkhead to see if it does allow access behind the fiberglass?

It does, but you either need an assistant or 6-foot arms at that point.

[Spittybug]

Just added my own 12V+ bus bar and used toggles. No problem. One is between the top two posts (in the original post hole) and the other is at the bottom of the bar in a new hole.