Floor pan popping

[Hindsight]

Someone posted about this long ago but I can't remember who and what the title was.

The heat from the welding that FFR does to the floor pans in the footwell area distorts them. They make a loud pop sound when someone gets in and then randomly driving down the road. It always startles the passenger when they get in and detracts from the overall "quality" feel of the car.

Short of cutting the pan out and welding a new one in place, has anyone successfully fixed this another way?

Thanks!

Jeff

[flynntuna]

https://thefactoryfiveforum.com/show...-China!/page11 post425

[Hindsight]

Thanks for the reply. Any more info on the technique? On mine, it seems like the entire pan pops, not just a small spot. Does heating and cooling it shrink or expand the metal?

[lance corsi]

I cut mine out & welded back a sheet of 11gage. It doesn't pop any more. It's the best way. I tried the heat shrinking method with little results, only to make more smaller warps. I also covered where the FFR fuel tank was supposed to be behind the seats. So little room in these cockpits that I moved my fuel tank forward under hood, using the original fuel tank area for behind the seat storage.

[Hobby Racer]

Here is another couple of posts;

This one uses heat
https://thefactoryfiveforum.com/show...Oil-Can-Effect

This one uses weld beads for the heat.
https://thefactoryfiveforum.com/show...l=1#post312132

I need to do something about my floors as well. Have not decided what method to go with.

[Hobby Racer]

I cut mine out & welded back a sheet of 11gage. It doesn't pop any more. It's the best way. I tried the heat shrinking method with little results, only to make more smaller warps.

What was your technique for not warping the new panels you welded in? I'm sure the FFR guys just lay in all the welds "hot-n-fast" to get it done. Did you skip weld it in small sections, add chill bars, what?

Also wondering how much strength the floor adds to torsional rigidity? I was thinking of cutting them out and putting in 1/8" aluminum plate instead. Welding small angle iron tabs to bolt the aluminum to.

[Mitch Wright]

I would think the easiest thing to do would be to cut a piece of one inch sq tube and welded it in a cross the center of the sheet metal section.

[flynntuna]

Has anyone had any success using dynamat to tame this?

[42Bfast]

Full disclosure, I'm building a roadster so I know NOTHING specific about the 818.

That being said, I just retired from a 32 year career in aerospace, aircraft manufacturing to be specific. (Industrial Engineering and Finance -- yeah, I know, strange mix.)

In our aluminum sheet metal assemblies we called that "oil canning". When we had that condition, one of the solutions, depending on the situation, was to add a stiffener to one side or the other, clearance dependent.

Basically, a strip of metal (multiple if required) in some strengthening configuration would be riveted across the offending section. One could use a "C" channel, "J" stiffener, or a simple angle.

Thus, to your condition, assuming you have access and clearance underneath, before you cut out the pan, try riveting a couple simple angle strips across the pan spaced apart and spanning the full width of the pan. The stiffener doesn't have to attach to anything structural to aid the situation. It basically spreads the load and, well, stiffens the panel.

Lots of the old British cars would utilize a crease or bead roll to stiffen the panels. Obviously you can't do that after the fact.

Worse case, if it doesn't work, you haven't invested much time, money, or effort, and you can go on to more drastic solutions.

Just a suggestion of something simple to try, coming from someone that doesn't have a clue about your specific application.

Hope it helps.

[flynntuna]

That's a good suggestion, especially since I won't be putting in carpet. I'll fabricate a large heel pad for both sides and either screw it down or rivet it in.

[lance corsi]

On my floor, I cut the old pan out and fully tig welded the new floor in. By the halfway point, it broke some tacks loose, but the 11gage steel did not buckle. I'm sure it stressed the framework, but all welding induces stress. I realize also that I increased the car's weight by 75 lbs, but being a floor, it didn't hurt my roll center and it is a trade off I'm okay with. Btw, my floor covers the entire bottom of my passenger compartment.

[Hobby Racer]

Here is a picture from the underside of the huge gap created by the buckling in the floor on the drives side looking toward the back of the car.

warbles.png

I'm thinking of cutting thin slots down the length of the buckle and then hammering the buckled section down and re-welding it back together. I really don't want to drill out all those rivets and pull the undertray aluminum off to fix it the "right way".

[NetWRX]

For what its worth my drivers side was like Hobby Racers. I stood on the floor pan and pushed all the ripples down, then put some strategic dents in it from the top with a hammer. If you stretch the metal down it makes it more rigid in that position and makes popping back up harder. You could also use a cold chisel or something similar to put a crease across it to improve rigidity. It saves the powder coat under the car, the top will likely be covered anyway.

[Doug @ Forma]

On our 818S we bonded a 1/4" sheet of material called PSG AluPOLY to the floor with M1 adhesive and that cured the popping. It's a polyethylene sheet with an aluminum skin on each side. We used it because we had it handy and knew it would be stiff enough. We suspect that something less expensive like ABS might work as well.

IMG_20170714_092750.jpgIMG_20170714_094341.jpgIMG_20170714_155018.jpg

[Hindsight]

Thanks for all the replies. A lot of good options here.