Trunk lid rivnut stripped - help

[jaga]

I stripped the rivnut in the trunk lid, bolt is stuck and rivnut is spinning in fibreglass lid. I managed to cut the bolt and get the trunk lid off but wondering how best to repair. I think I will need to cut the stripped nut out, repair the fibreglass and install a new rivnut.

Any recommendations on what to use and how best to do this?

Thx,
Jaga

[SteveP]

I don't know an easy way to remove them. If you can get vice grips on the edges you may be able to gently drill them out. It is a fairly common problem and the main reason not to use rivnuts. Nut plates are probably a better solution but you have to have access to the back side. Aircraft Spruce sells them and they will send you a nice catalog if you give them a call. 877 477 7823. Spruce also sells good quality rivnuts with ribs to help secure them.

[cv2065]

I think I drilled a couple out early in the build. Had to get a larger sized rivnut to replace.

[65 Cobra Dude]

I use this and rivet it where the hinges and striker mount. This gives the rivnut more bite.F0285905-AB1E-4D9A-B248-2AEE7B3969FC.jpg

Henry

[NAZ]

I stripped the rivnut in the trunk lid, bolt is stuck and rivnut is spinning in fibreglass lid. I managed to cut the bolt and get the trunk lid off but wondering how best to repair. I think I will need to cut the stripped nut out, repair the fibreglass and install a new rivnut.

Any recommendations on what to use and how best to do this?

Thx,
Jaga

Yes, you can cut out the fiberglass and make a repair or you can drill out the old rivet nut and install a new one. To make a correct repair you need advanced skills for either of these two options.

I prefer to drill them out. Now, here's where the skill comes in. This is similar to removing a broken bolt in a threaded hole. Most inexperienced with this will not take the extra time and effort to drill a pilot hole directly in the center and just think close enough will work. They end up destroying the hole the fastener is screwed into and end up drilling a larger hole and using a larger fastener but the hole is never quite in the same place as it was originally. A skilled craftsman will take care to mark the exact center and drill a small pilot hole.

So if you have the patience to do the job correctly AND you have the tools, there will be no need to repair fiberglass or use a larger fastener. Remember, to achieve acceptable results you need the skill, knowledge, and tools to do the job correctly. Shortcut any of these and you may not be happy with the results.

First step is to grind the broken fastener flush with the flange on the rivet nut. Go slow and keep it flat. From there you need to precisely mark the center of the rivet nut. This is where the skill comes in. There are various ways to find the center depending on what you're dealing with. What may work best for you is to use a transfer punch about the same diameter as the flange on the rivet nut. That way you align the punch concentric with the round flange and tap the punch lightly to make a witness mark. You can then use a center punch to crater the witness mark.

Start with a small drill ~.070" to make a pilot hole directly in the center of the rivet nut and drill through the stuck fastener. From there it's a simple matter of progressively increasing the size of the hole until you finish with the drill size needed for the size rivet nut you're drilling out. The final cut will completely drill through the body of the rivet nut leaving the flange on your drill bit. If you've done everything correctly the hole will still accept the same size rivet nut.

But if using rivet nuts in plastic, I suggest you use the type made for plastics. I get mine from McMaster-Carr but there are other sources. Here's an example: https://www.mcmaster.com/97217a393

[sread]

I think the real difficulty in drilling out the old rivnut is the fact that it now spins in the hole. As soon as the drill bit bites the whole thing spins and there is no easy way to hold it.
Keep in mind that when you do get it out and go to install a new one, there are aluminum body rivnuts and there are steel body rivnuts. The aluminum ones are very easy to strip out and in fact are quite easy to pull the threads out when you are installing them.
Any type of rivnut in thin fiberglass is never going to be an ideal solution and will suitable only for light duty use.
Some type of added reinforcement (metal or maybe epoxy) will go a long way to prevent more problems.

[NAZ]

I think the real difficulty in drilling out the old rivnut is the fact that it now spins in the hole. As soon as the drill bit bites the whole thing spins and there is no easy way to hold it.
Keep in mind that when you do get it out and go to install a new one, there are aluminum body rivnuts and there are steel body rivnuts. The aluminum ones are very easy to strip out and in fact are quite easy to pull the threads out when you are installing them.
Any type of rivnut in thin fiberglass is never going to be an ideal solution and will suitable only for light duty use.
Some type of added reinforcement (metal or maybe epoxy) will go a long way to prevent more problems.

Perhaps you haven't tried the rivet nut designed for plastics. For these to pull through they would take a huge chunk of fiberglass with them -- think more than triple the size hole you originally drilled.

As for the rivet nut spinning while drilling, there are a few methods I've used successfully to combat this. First try holding the flange with small needle nose vice grips. Second is to drill a small hole through the flange and into the base material (~.040") and insert a short length of .032" safety wire into the hole to stop rotation. These usually work when using a conservative approach to stepping up in drill size, especially on alum rivet nuts. If these won't stop the nut from turning you can use a rotational approach to drilling but this is harder to explain than to demo and I can't demo this through the forum.

[Jeff Kleiner]

Any type of rivnut in thin fiberglass is never going to be an ideal solution and will suitable only for light duty use.
Some type of added reinforcement (metal or maybe epoxy) will go a long way to prevent more problems.

FYI, these rivnuts are not just installed in fiberglass; there is metal under the 'glass in the hinge mount area. If it spun it either wasn't pulled fully when installed or the 1/4-20 stainless screw galled or was cross threaded.

Jeff

[sread]

FYI, these rivnuts are not just installed in fiberglass; there is metal under the 'glass in the hinge mount area. If it spun it either wasn't pulled fully when installed or the 1/4-20 stainless screw galled or was cross threaded.

Jeff

that's what I was thinking - I haven't fully installed the trunk lid yet but did install the hinges and thought there was metal behind the glass. I wasn't sure if the OP was referring to those particular fasteners. Do you know if there is metal reinforcement in the area where the striker mounts?
I do have some of the rivnuts Naz is talking about but haven't tried them yet. I seem to recall they may need a little more depth behind them to insert for installation.

[edwardb]

Do you know if there is metal reinforcement in the area where the striker mounts?

If you mean for the doors, yes. There's metal on the door frame inside for the latches. If you mean for the trunk lid, no. At that location for the handle, the inner and outer shell are basically touching, so it's solid fiberglass. You'll use through bolts there. Also for the license plate mount and light.