Fender Mount Problem

[Honcho]

I did a boo boo. This is a really tough one. Last night, I decided to finalize all of the panel gaps on the car. As I was spinning the right fender lower bolt, the rivet nut in the body snapped off. So, yeah. The nut insert is still threaded on the bolt, so it's stuck in the hole. I cannot get any tension/friction on it to back the bolt out. If I take the blade off of my hack saw, I think I can get it in there to cut the bolt. I'm considering the following options, all of which sound bad:

Cut the bolt options:

• Glue the fender to the body with panel adhesive. No idea how to clamp it though. While I think the panel bond will keep the fender in place (the other bolts will hold it firmly to the car), I don't love this because the side sill mounts to the fender and that's a lot of load for just glue.
• Drill another hole through the fender and side sill (after making triple-sure the panel gap is correct- you only get once chance to get it right!) and use a sheet metal screw to hold it in place. It's only a 7 lb/ft torque on that area, so this should be more than enough to hold it. But, it seems like a very redneck way to solve the challenge.
• Fill the existing rivet nut hole with JB Weld epoxy putty, drill a new hole in that and then use a sheet metal screw to mount the fender using the existing hole.
• Take the car to my body shop, which can weld aluminum, and have them drill out the entire rivet nut and weld a new one in there.

Keep the bolt options:

• Glue the fender to the body with panel adhesive, including some on the bolt to stop it from rattling.
• Drill another hole through the fender and side sill (after making triple-sure the panel gap is correct- you only get once chance to get it right!) and use a sheet metal screw to hold it in place. Again, put glue on the old bolt to stop the rattle.

There is a 30mm grommet right next to this area and I'm hoping that it allows access to the inside of the side sill extrusion. if so, I can get a magnet in there to remove the bolt end after it drops.

NSX Prime family- HELP!

 

[Old Guy]

First off, I am not a fan of the glue idea. Not because it won't be strong enough; but, because it complicates future work if it ever should be required. If there is sufficient matched mating surface between the fender and the body extrusion to allow a proper thin joint the glue can make for a very strong and very 'permanent' connection.

I assume that the kind of L shaped piece on the left side of the photo is the edge profile of the fender with the bolt going through it into the failed rivnut? If you cut the bolt off allowing access to the hole, depending on what remains of the original rivnut body your fill with epoxy solution might work. However, from my rather limited experience with rivnuts the failure point is frequently shearing of the thread body where it attaches to its mounting flange. If that is the case I don't think you have enough material left to create a good epoxy plug to accept a sheet metal screw.

Without having eyes on the actual problem area my preferred solution would be to install a new rivnut in the existing hole. Depending on what the problem area looks like, this might be a smaller rivnut in the existing hole or drill out the remains of the old rivnut to install a new rivnut. That bolt looks like it might be about an M6 which is approximately 1/4" and I have installed 1/4" aluminum rivnuts by hand without a lot of effort. Rivnuts are available in metric sizes and you should be able to find M6 in aluminum (which is a hell of a lot easier to install than the stainless or galvanized / zinc coated steel versions). I would think that aluminum would be the preferred material and should suffice because of the relatively low installation torque.

I will leave it to your creativity as to how you retrieve the bolt remains. I have had very good luck using an 18"' long piece of stripped #12 or #14 copper house wire with a little 1/4" magnet glued to the end. The copper is easy to bend to get into tight spaces to wiggle around searching for errant screws and the like. I have had one in my tool box for 30+ years.

The weld a new nut in place would probably work; but, after going to all that work on the paint I would be suffering from seriously chapped cheeks because of the paint damage.

 

[Honcho]

First off, I am not a fan of the glue idea. Not because it won't be strong enough; but, because it complicates future work if it ever should be required. If there is sufficient matched mating surface between the fender and the body extrusion to allow a proper thin joint the glue can make for a very strong and very 'permanent' connection.

I assume that the kind of L shaped piece on the left side of the photo is the edge profile of the fender with the bolt going through it into the failed rivnut? If you cut the bolt off allowing access to the hole, depending on what remains of the original rivnut body your fill with epoxy solution might work. However, from my rather limited experience with rivnuts the failure point is frequently shearing of the thread body where it attaches to its mounting flange. If that is the case I don't think you have enough material left to create a good epoxy plug to accept a sheet metal screw.

Without having eyes on the actual problem area my preferred solution would be to install a new rivnut in the existing hole. Depending on what the problem area looks like, this might be a smaller rivnut in the existing hole or drill out the remains of the old rivnut to install a new rivnut. That bolt looks like it might be about an M6 which is approximately 1/4" and I have installed 1/4" aluminum rivnuts by hand without a lot of effort. Rivnuts are available in metric sizes and you should be able to find M6 in aluminum (which is a hell of a lot easier to install than the stainless or galvanized / zinc coated steel versions). I would think that aluminum would be the preferred material and should suffice because of the relatively low installation torque.

I will leave it to your creativity as to how you retrieve the bolt remains. I have had very good luck using an 18"' long piece of stripped #12 or #14 copper house wire with a little 1/4" magnet glued to the end. The copper is easy to bend to get into tight spaces to wiggle around searching for errant screws and the like. I have had one in my tool box for 30+ years.

The weld a new nut in place would probably work; but, after going to all that work on the paint I would be suffering from seriously chapped cheeks because of the paint damage.

Thank you! I hadn't even considered a rivnut, but it would be the best option. The existing one failed just as you described: the thread body broke off where it joins the flange. I wasn't even turning it that hard- I suspect with all the front end work/damage this car had perhaps that joint was already compromised or over-torqued in the past. Yes, the bolt is a M6 and the remaining hole is about 1/4". I was thinking about using a M5 rivnut and just drilling out the existing flange to fit it. I've seen several DIY rivnut tools on the interwebs- basically a bolt of the same thread, a nut and two washers. Agree that Aluminum is ideal.

Now, I need to cut off that bolt. Using a hacksaw blade and leather work gloves. And not nicking the paint. Maybe I'll just build out the trunk instead lol.

 

[MotorMouth93]

I agree, using a new rivnut in the same hole sounds like the best approach if at all possible. Carefully cutting the bolt (with adequate amounts of masking tape protecting the body and fender) then drilling out the existing rivnut might allow you to remove the remains of the old one before installing the new one.

 

[jwmelvin]

Yea I’d try hard to get rid of the existing rivnut before putting in a new one.

 

[Old Guy]

If you are going to try the rivnut and you have not used them before, purchase some aluminum sheet from Lowes or Home Depot in roughly the same gauge as the fender and do a few practice runs installing the rivnut. On the smaller rivnuts that I have installed I have always used the allen bolt with conical spreader thing to install them and they can be a little fiddly and you can bugger up the install so a little practice is good. I have never used the pop rivet style insertion tools.

 

[JohnWayne]

After reviewing the options, I think the best course of action is to sell the project.

 

[docjohn]

did you pm Joe?

 

[Honcho]

I agree, using a new rivnut in the same hole sounds like the best approach if at all possible. Carefully cutting the bolt (with adequate amounts of masking tape protecting the body and fender) then drilling out the existing rivnut might allow you to remove the remains of the old one before installing the new one.

Yea I’d try hard to get rid of the existing rivnut before putting in a new one.

My first attempt will be to see if I can fit a 5mm rivnut in the 6mm rivnut hole. It's not a lot of installation torque and I'm really, really nervous about drilling out the factory rivnut. If I can avoid that and still get a secure hold, I'll call it a win. But- real talk- I'll probably end up drilling it and using a new 6mm LOL.

If you are going to try the rivnut and you have not used them before, purchase some aluminum sheet from Lowes or Home Depot in roughly the same gauge as the fender and do a few practice runs installing the rivnut. On the smaller rivnuts that I have installed I have always used the allen bolt with conical spreader thing to install them and they can be a little fiddly and you can bugger up the install so a little practice is good. I have never used the pop rivet style insertion tools.

Good advice. I bought some metal for mounting the interior bluetooth speaker and license plate. I'll have plenty of scrap to practice on. I'm going to use a steel 5mm threaded bolt, a couple of washers and two nuts to install.

After reviewing the options, I think the best course of action is to sell the project.

For $500,000, it's yours!

did you pm Joe?

Not yet. Gonna try to get myself out of this jam first.

This weekend, I decided to hide from reality and build out the trunk, rear bumper and tail lights instead. The JDM tails and S-Zero "H" look amazing on the Imola. I'll face the rivnut challenge later this week...

 

[Honcho]

Quick follow-up: repair successful. I decided to mount the 5 mm rivnut into the carcass of the OEM 6 mm rivnut. Total success.

The tools.

The old rivnut body.

The new 5 mm rivnut installed.

The new 5 mm bolt and washer. Since these are zinc-plated steel pieces, I treated them with the silicone grease for added corrosion protection.

 

[Old Guy]

Excellent, and it looks like you have a lifetime supply of 5mm inserts to cover any future 'Oh f***' moments.