MGB - floor pans (Part 2)

Today we continue the saga of replacing the floor pans in the MGB. In Part 1 (See MGB - floor pans Part 1), we identified the issue, and made decisions on parts and a method. Today, we get into removing the old pans.

Get Safe

$15 at Harbor Freight

This could be a euphemism for something else, but in this case, it is exactly what it says: safety first. You are going to be cutting and then welding steel. This throws lots of sparks. Your car runs on gasoline which is designed to explode when a vapor meets a spark. When you put these together, my best advice is to remove the fuel system entirely and then wait a couple of days to let the fumes leave the remaining lines. That's what I did, and I'll post on that later. Consider too, that the cutoff wheel throws dirt and dust everywhere so wear eye protection at least. I use a face shield, long sleeves, and denim pants to protest myself. And yes that gets hot in the summer when you're working in the sun on your driveway.

Clear Your Paths
Under the right (passenger in the US) side floor, there are small pipes and cables that you don't want to set your cutoff wheel into. These pipes and cables are held to the floor underside with nuts and brackets, and further held into place with some rubber bits. Remove the nuts and the brackets and pull the rubber bits out. Toss all of it into a ziplock and mark it as part of the right floor. You'll want them later. Let the cables and pipes hang as far out of the way as possible. Among these is the fuel feed line, the vapor line and the main power supply from the battery. All super important.

blue tape the cut lines

I had the brake and clutch pedals already removed from my efforts on the master cylinders (post on that coming). I chose to remove the accelerator pedal as well to improve my access. Since it is held on with a bolt and the cable is held on with a pin, this removal is very easy. Now that my floor has been removed, I couldn't imagine how much harder this would have been with them still in place. Mental picture: you're lying down on the door frame, hips-to-feet sprawled out through the driver-door, with your arms extended into the foot-well with a grinder spinning a cut-off wheel at 11,000 RPM. Getting the cuts right without accidentally catching the underside of the brake pedal sounds virtually impossible. I highly recommend removing the pedals, if you can.

Mark the Spot
Before you grab your grinder, you need to find the frame sections underneath. On the right (passenger) side, I followed instructions I found online, where I drilled holes at the corners of various support structures. I then connected those dots with blue painters tape and then drew on those lines with a sharpie so I had clear lines to follow. This did work, but for the left (driver in the US) side, I thought I could do it with fewer steps. The first step is the same: with one had under the car and the other resting on the top of the floor, tap with your bottom hand at the corners of the beams. Feel for the tapping with your top hand, and keep circling in on the spot by tapping until you know exactly where the spot is. Mark it with a sharpie. On the right side, I drilled a hole. On the left, I just marked it and moved on. I ultimately found that the drilling was unnecessary. There are 2 main under-floor rails, one runs from the transmission hump to the edge under the front seat mounts. The other runs from that cross rail between the legs to the front. In the US model, imagine a rail running straight at the brake pedal. These rails are about 2 inches wide, but there is only about 1/2" lip that it spot-welded to.

not-so-fun part

Measure Twice, Cut Once
This phrase has been made famous by arm-chair trades-persons dating back to the stone cutters in Egypt. Still, its a good practice. Double check your marked lines to make sure that you didn't draw a line through a section of frame. Also consider if your cut-path will send you through any of the cables or pipes you moved aside earlier. Cutting through a fuel line, even if it's empty, really sucks. Yes, I did and I'll explain how I fixed it later. Along the rear edge, there are two heavier sections in the corners that are not to be cut out. They create structural stability and should only be removed it they are not doing that job. My bar had a pretty rusty floor, but those sections were fine. Make sure your cut lines take these sections into account.

The Fun Part
The floor is cut out in 3 or 4 sections, separated by the frame rails. Cut the rear out first. The rear section comes out as one large, nearly square piece, and the steel cuts pretty quickly once you get started. With the rear cut and pulled out of the way, you can see the cable, etc on the right side. Next, I cut the outer of the two forward sections. Again, this allowed me to avoid the cables, etc on the right (passenger) side. Last, I cut the inner section, and it was all pretty clean except I nicked the fuel line for about an inch, leaving a nice gash in the metal fuel line. At this point, I was glad I'd pulled the fuel tank, and let the system sit for a week or so.

The Bit

spot weld cutter

With the main sections of the floor out of the way, it feels like you're really on your way. That's until you start to understand what comes next. The floor was attached to the rails at the factory with a big spot-welder, placing a weld every inch or so along both rails and around the outer edge. Those spot welds are what is holding that last inch of steel to the car. I have read where some folks (who are far more skilled with a grinder than I) were able to cut these sections off without any other tool. High praise to them. I am no way skilled enough for that, so I went the more labor-intensive route.

Hit Harbor Freight and buy at least 2 spot-weld cutting bits. They are small, fit in your drill, like a regular drill bit, but they are designed to cut spot welds. The shiny, silver point in the center of the bit is set into the center of the weld, and then you run the drill at a slow speed to cut the sheet metal around the weld. This allows the rest of the sheet metal to rise from the rail. Each bit is reverse-able, so as you burn out the teeth, you can pop it into a vice, loosen it with a 1/4" spanner, flip the bit and tighten. One bit lasts twice as long... which still isn't that long if you run your drill too fast.

So, now that you understand the weld-cutter, slap a grinding wheel or wire wheel onto your grinder and grind on the remaining bits of floor so you can find the spot welds. Between rust, paint and black-tar seam-sealer, you may have to grind a bit to find the spot welds. If you can't find them all or you don't want to grind to find them, there is an alternative; you just need to be willing to use a framing hammer and chisel.

The Not-So-Fun Part

cleaned up

With your spot weld cutter in your drill, and a framing hammer / chisel nearby, pick a spot to start. I went with the easiest to get to: the rear section. The spot welds are easier to find back here too. Pick a spot weld, cut it out (slowly on the drill!). If the metal didn't make a "ting" noise while cutting, it may not be completely free. Given time you'll get the hang of it where you're not cutting too deep (through the frame) nor too shallow (and leaving the metal well attached). If the metal didn't separate, get under the metal edge with your chisel and give it a couple of smacks with the hammer. Eventually, the floor and rail will separate. Now do that about 120 times. Per side. I spent about 4 hours per side doing this, so be prepared. Now, I do things slower than lots of people, so maybe you'll be a lot faster.

As you remove flooring, the remnant will start to flop around. On my first (right/passenger) side, I just crumpled the metal out of my way. While this worked, I found that by cutting strips in straight sections (using tin snips) was more effective. And, ff you set them aside with the larger sections of floor you cut out, you can re-create the shape of the floor later.

Clean It Up

temporary protective paint

Once all of the spot-welded in bits of floor have been removed from the rails, you're ready to clean up. First, look at what you've done. There is a pile of twisted sheet metal lying on the ground next to your car. The rails have some holes drilled through (I know mine sure did). The rails have like 100 little circles of flooring still attached, there's some rusty spots, some paint, and probably some seam sealer. All of that needs to be taken down to bare metal for welding. Grab your grinder, put in a good grinding wheel and get after it. To me, this was the most satisfying part of the process to this point: Simply grinding away the ugly and leaving a nice clean shiny rail. Once the weld points are nice and clean, I switched over to a wire wheel and removed all of the surface rust I could find in the foot well, along the transmission tunnel and the rear, effectively grinding away all of the rust in the seating tub.

Since I was not going to be working on the project for a while, I shot the cleaned up space (including the rails) with primer and some orange Rustoleum so I wouldn't have new rust appear while I was away. This meant I got to grind that paint off later, but if you're not going to jump right into welding, I'd encourage you to consider the same.

That's it for today. More next time. Thanks, as always, for following along-