Installing rivnuts through floor over frame rails?

[VanGoSki]

There's an extra deep channel in the floor directly over the frame rails. I'd like to attach some L track directly over the rails. It seems like the easiest way would be to use rivnuts. It appears that there's two layers of steel there, the top of the rails and the floor and I'm not sure if that will mess things up. Rather than drill a test hole and try it, I figured I'd just ask and see if anyone has done this. Or barring that, if anyone knows if there are any issues with doing it.

Here's a picture of the channel with a factory bolt hole for a floor anchor. I hope to run my L track directly over this channel.

Many thanks in advance.

 

[sprint2freedom]

I haven't done that but I did set 1/4-20 rivnuts in places on the van where there are two layers of steel overlapping and spot welded together. Specifically at the nexus of the standard height side wall and the high roof where those body pieces join together.

I didn't have any real issues but everything about the process was harder. Harder to drill, harder to deburr, harder to set the rivnut, etc. Take your time, take breaks, and don't expect it to go quickly.

One pitfall I can see with doing this in the floor is the added thickness of the undercoating, although I guess in your case there isn't any because it's inside a frame rail?

 

[Eric Experience]

Vangoski.
When you purchase riv nuts you can specify the clamping thickness so you should have no trouble getting rivnuts to do your job. If you use metric units you should be able to get a much wider range of products. Eric.

 

[Midwestdrifter]

You need enough clearance below the nut obviously. Then select the rivnut with the appropriate grip range for the thickness of material buildup. Otherwise I don't see any issues with your proposal.

 

[VanGoSki]

I haven't done that but I did set 1/4-20 rivnuts in places on the van where there are two layers of steel overlapping and spot welded together. Specifically at the nexus of the standard height side wall and the high roof where those body pieces join together.

I didn't have any real issues but everything about the process was harder. Harder to drill, harder to deburr, harder to set the rivnut, etc. Take your time, take breaks, and don't expect it to go quickly.

One pitfall I can see with doing this in the floor is the added thickness of the undercoating, although I guess in your case there isn't any because it's inside a frame rail?

Thanks. Yes, being in a captive area should mean less corrosion too I imagine.

Vangoski.
When you purchase riv nuts you can specify the clamping thickness so you should have no trouble getting rivnuts to do your job. If you use metric units you should be able to get a much wider range of products. Eric.

You need enough clearance below the nut obviously. Then select the rivnut with the appropriate grip range for the thickness of material buildup. Otherwise I don't see any issues with your proposal.

Thanks, guys. I didn't know that rivnuts came in depths for different thickness materials. That's great to know.

 

[Airtime]

There's an extra deep channel in the floor directly over the frame rails. I'd like to attach some L track directly over the rails. It seems like the easiest way would be to use rivnuts. It appears that there's two layers of steel there, the top of the rails and the floor and I'm not sure if that will mess things up. Rather than drill a test hole and try it, I figured I'd just ask and see if anyone has done this. Or barring that, if anyone knows if there are any issues with doing it.

Looking at the Mercedes BEG (page 61) I believe those are non-drill areas.

 

[VanGoSki]

@Airtime Thanks. I'm curious which BEG you're looking at. My Sprinter 2019 907 BEG dated 06/2018 doesn't have those diagrams. It is still pretty clear that you shouldn't drill through the top and bottom flanges of the frame rails though, so no argument there.

Hmm, now I'm torn....

 

[Airtime]

It's from the 2020 BEG, publication date 12/2019. The 2019 BEG has text but not pictures. And I think 2020 and 2019 bodies are the same in this regard.

 

[VanGoSki]

Gotcha, thanks. So would you do it?

 

[OrioN]

Gotcha, thanks. So would you do it?

"Mike told me to do it!"

 

[VanGoSki]

"Mike told me to do it!"

I value his opinion. You find that amusing?

 

[Airtime]

Gotcha, thanks. So would you do it?

I don't think so, not without more info and/or a knowledgable engineer looking at it. The way Mercedes is pretty black and white about that, adding pictures and arrows makes me think it's important. And without knowing more about why, I'd be hesitant to second guess that.

 

[RVBarry]

How many inches are those from the wall? The factory rails are around 15", iirc.

 

[Airtime]

How many inches are those from the wall? The factory rails are around 15", iirc.

That's a really good question. I just measured mine and it is about 13+ inches from the D-ring bolt to the outer edge of the frame, forward of the wheel wells. The D-rings are about 3- inches from the wall, so if I measured right then I think the frame is from 16-19 inches from the wall. Maybe they bolt it to the flange on the frame, just outside of its outer wall?

The blue areas shown as do not drill are in between the frame walls. The flange on the frame member is not colored blue so looks like that may be OK? It would explain the 15" location for factory rails.

 

[Eric Experience]

Vangoski.
That instruction probably came as a result of some very stupid holes drilled in vans for drainage or other plumbing. I have tried to repair large holes like 75 diameter in rails. In your case you are planning to add stiffness to the rail by clamping a rail on it. If you use M8 screws about 200 apart you will end up with a very similar strength in the floor. The greatest stress on the floor is from excess tyre pressure. Eric.

 

[DanAzon]

Gotcha, thanks. So would you do it?

I find it difficult to believe a 17/32 hole would cause catastrophic structural failure to the frame of a 3/4 ton truck. Let 'er rip VanGoSki, don't lose another ear over it.

 

[VanGoSki]

@RVBarry 16.5"

 

[RVBarry]

@RVBarry 16.5"

That's a really good question. I just measured mine and it is about 13+ inches from the D-ring bolt to the outer edge of the frame, forward of the wheel wells. The D-rings are about 3- inches from the wall, so if I measured right then I think the frame is from 16-19 inches from the wall. Maybe they bolt it to the flange on the frame, just outside of its outer wall?

Sounds like the right place. I don't see a problem (not an expert).

You have a cobalt drill bit?

 

[VanGoSki]

Vangoski.
That instruction probably came as a result of some very stupid holes drilled in vans for drainage or other plumbing. I have tried to repair large holes like 75 diameter in rails. In your case you are planning to add stiffness to the rail by clamping a rail on it. If you use M8 screws about 200 apart you will end up with a very similar strength in the floor. The greatest stress on the floor is from excess tyre pressure. Eric.

That's a great point about the L track actually adding stiffness. Add in the fact there's multiple layers of steel in this area and I'm fitting rivnuts in there, it just doesn't seem like it would be weakening anything. But it is against the BEG for whatever that's worth.

I find it difficult to believe a 17/32 hole would cause catastrophic structural failure to the frame of a 3/4 ton truck. Let 'er rip VanGoSki, don't lose another ear over it.

LOL, good one. And I think I agree.

 

[DanAzon]

That's a great point about the L track actually adding stiffness. Add in the fact there's multiple layers of steel in this area and I'm fitting rivnuts in there, it just doesn't seem like it would be weakening anything. But it is against the BEG for whatever that's worth.

LOL, good one. And I think I agree.