Standard Safety Precautions
Like any job, block your wheels, put it up on jack stands if you can't work on it while it's on it's wheels. Since you're working with fuel, at the very least make sure your garage doors are open with a fan blowing on your work area or better yet do this job outside. Obviously, don't smoke or have your friends/kids/wife playing with a welder or blow torch while you're doing this. I'm not your mom, so if you choose to slide under your car without eye or face protection, that's entirely up to you. Personally, I like being able to see things like sunsets and my wife's face, so I wear at least safety glasses, if not a full face shield anytime I'm working on a car. Honestly, the number of times I brain myself on my car has me thinking about wearing a hardhat too.
Free Your Lines
Fuel tanks are all very similar: there's a big hose to get fuel in from the pump, a small hose to supply the engine with fuel and there are vents (at least one) on the top that have lines that lead up to the engine (after routing through charcoal or something) for inclusion into the air that the engine uses at combustion time. On fuel-injected vehicles, there is an additional line for a return from the engine. When the engine doesn't require all of the fuel that the system has pressurized, like when you're decelerating, the excess flows down that fuel line back into the tank. So, once you know what you're looking for, you need to remove them from your tank before you remove the tank itself. First, remove the vent lines. these may not be the easiest to get to, but they will definitely NOT have fuel in them, so you shouldn't need a pan. Make note of where the rubber hose came from when you set it aside. You'll want to cut a replacement that's the right diameter and length at install-time.
|trunk underside - before|
Last, remove the filler hose. In the MGB, this was the easiest part. The filler hose runs from the rear next to the passenger tail light through the trunk and into the top of the fuel tank. It is secured with a simple, albeit big, hose clamp.
Before you can drop the tank, disconnect the wires from the fuel level sender. Depending on the car, the fuel level could have both a signal wire and a ground -OR- it may only have a signal wire. This means that the sender gets it's voltage difference basis from a ground through the tank itself. If this is you, consider a means of improving that ground, especially if your fuel level gauge is a little flighty, like mine.
This is the fun, satisfying part. I put my ATV jack under my tank to support it while I removed the nuts and bolts. Since there will inevitably be some fuel left in the tank after siphoning, you don't want that weight bearing on the fasteners, and then have the tank suddenly drop when the last one comes free. Some tanks are held on with a pair of straps. My old Camaro was like that, and many older American cars are too. These come off with a couple of bolts. The MGB tank is held on with nuts/bolts around the outside lip where the top and bottom sections of the tank come together. In total, there were 9 fasteners: four along the one side, 3 along the other, 2 across the rear. I guess the engineers couldn't make up their minds and be consistent. The ones in the rear can be a little tricky to get to. Once out, the rear edge of the tank can get hung up above the bumper so tilt the front down first and slide forward.
Drain, Clean and Dry
Once on the ground, remove the fuel level sensor. On the MG, it is held on with a spin-on ring that lets go after a couple of taps with a hammer. Set the sensor aside for testing, and then drain the remainder of the fuel through either the fill hole or the fuel level sensor hole. Depending on how old the gas was, you may need to recycle what is now in your catch-pan. Mine was relatively fresh so I used it in my lawnmower.
At this point, I refer to my friends at Mac's Radiator. They cleaned, lined and painted the tank for the bus a few years ago, and I want the same treatment for the MGB. For about $300, your original tank is better than new, you don't have to pay oversized shipping, you know it will fit and best of all... its a genuine shipped-with-the-car original part. In the MGB case, you can no longer buy a true original. The aftermarket tanks generally don't have splash baffles (prevents the fuel from sloshing around when you corner), and some don't have vents. They aren't lined (so they may start rusting from the inside) and they are of inferior, thinner steel. Still, I did find one for $170 plus shipping that "are made with corrosion resistant Ni Terne steel to fight of rust and ethanol fuel". This is from a less-than-best distributor here in Oregon (poor return policy), British Parts Northwest, and again, it isn't lined. Part link here. Of course, good work isn't fast, so it will be a couple of weeks of waiting before I have it back, ready to install.
While your tank is at the radiator shop, test the fuel level sender. Rather than re-hash, here is a fantastic article for testing and calibrating the fuel sender and gauge. My float would not give a consistent reading below about 100ohm (or from a half tank to full tank), so it will be replaced.
The parts list is actually longer than I had anticipated. Looking at the picture above, the newer shaped tank is on the right. It bolts up directly under the trunk, so rather than having steel on steel, there are foam "straps" that fit between. There should also be a seal around the edge of the filler neck. Add the fuel-level sender. I also added in a new sender seal and locking ring. Of course, I'll be using all new 5/16" fasteners and rubber lines from the tank to vent and engine fuel-supply. Once assembled, everything related to the fuel tank and supply to the engine will be refreshed.
|trunk underside - after|
When the tank is returned from the radiator shop, it should have a protective coat of paint, but if your shop is anything like Mac's, they highly recommend a thicker, more protective coating. So, sand an edge into their paint, then prime, sand, wipe and paint with a suitable topcoat. Since this is not going to be seen, this doesn't need to be the expensive body paint, but something chip-resistant makes sense, since it will be exposed to the road. Once cured, install the level sender with the new seal, making sure the fuel pick-up tube is pointing toward to bottom of the tank.
Since the steel tank sits up against a steel trunk floor, the MGB was originally outfitted with foam strips to set between. As you can see by the parts picture above, these foam strips run front to back. They are purchased as a roll and need to be cut-to-fit., It is very possible that you could save a few bucks and get basic home insulation strips at a big box store. The parts vendors assure me that the real deal are gasoline resistant, so the extra few dollars are worth it. Your choice. I bought the real parts since I was getting a bunch of other stuff anyway.
Last, set the foam collar around the fuel filler inlet. This needs to be in-place before the tank is installed.
|the contrast between new and old|
That's it for today. I only got after the fuel system because I had to do some welding, but I'm glad I did. Rust hides. If you don't get into the little crevices, you won't see what's growing until it's too late. The top of the tank looked horrible, but once the rust was arrested, the remaining steel was thick enough to last another 40 years. As always, thanks for following along-