of AC's post-war 2 Litre Saloon

Fuel Tank, Pipe and Filter

The AC's fuel tank is constructed in the old traditional way, from steel coated in 80/20 solder, and then soldered together. Presumably, that means that a fire will cause a fuel leak! That is all the more reason to keep your precious AC safe from fire risks. The good news is that the solder coating preserves the steel tank very effectively, so that reduces one potential risk of leakage.


If you have not dismantled the car as part of a restoration, then there are a few bits and pieces to remove before you can get your hands on the tank. The plywood partition in the boot (trunk) needs to be removed. Mine had previously been cut into two parts, probably by AC themselves, making it much easier to take out. Remove the rear seat and the trim from behind the backrest. I'll leave it to your initiative as to how best to drain out the fuel, noting that earlier ACs had the fuel filter mounted lower than the tank, on the bulkhead, making it a useful drainage point.

Remove the rear shelf trim to reveal the two coach-bolts that the tank hangs from. Remove the 4 nuts from the front of the tank, and disconnect the rubber hose to the filler. It helps if you can unstick the two hose-clips from the filler-hose, after which the filler-cap complete with hose can be lifted out. Remove the outlet pipe (90 deg. bend). Taking out the gauge sender-unit, also gives a little extra room. The tank will pull out through the boot, although this might turn into a lengthy wrestling match! The boot-lid will need to be either removed, or opened out horizontally.

Cleaning up

The outside of my tank was originally coated with bitumen, which I scraped off with a heavy duty scraper. Don't use any power-tools to remove the paint/coating, because of the lead in the solder coating.

Old petrol left to stand, deposits a varnish. This varnish crumbles to a fine dust when dried out, which resembles rust, so don't panic thinking the tank is rusting away, when a pile of reddish-brown powder comes out!

I'm not dancing with R2D2's little brother. I'm cleaning out the petrol tank.

To clean the inside, I used some POR15 Cleaner Degreaser, diluted, plus some old nuts and bolts to rattle around in the tank to dislodge rust and varnish. I sealed all the openings with heavy-duty tape and turned the tank around, shook it, and left it to stand on each of its six sides in turn (at least 20 minutes each side). After draining out the cleaner, I kept repeating until clean. I have a borascope, and was able to examine the condition and cleanliness of the inside.

This isn't a sunken ship wreckage. It's the inside of my fuel tank after cleaning, with a baffle visible to the left. The horizontal solder seam (on the front side of the tank) can be seen to the right.

Tank filter

The tank outlet pipe incorporates a double gauze filter. This consists of an extremely fine brass gauze wrapped into a tube, with a coarse gauze outside it, and a brass cap to seal off the top. This was largely blocked up, so I dipped it in that same POR15 Cleaner Degreaser, and within a few minutes, it came out shining. The very fine inner gauze was already slightly damaged, with larger holes through it. I'm not sure if it is worth repairing, since it is so prone to blockage?


I gave the inside of my tank the same phosphoric acid treatment as I do for steelwork that I paint. I stuck with the POR15 brand and used their "Metal Prep". The procedure was similar to cleaning out the tank, with all internal sides getting a treatment for at least half an hour each. Sloshing the liquid around, helps to treat the two baffles in the tank. Extra care needs to be taken, since this is an acid, so wear goggles and suitable gloves. I found that a small pile of rust flakes came out afterwards.

I decided not to use any kind of tank sealant. It is not needed unless the tank condition is fairly poor - perhaps with some pin-hole leaks. Applying tank sealant presents a challenge, since you need a very clean surface inside, but obviously have a limited view and access. A borascope would be really handy for this. If the sealant doesn't stick well, then it can cause serious problems if it comes loose.

Fuel gauge sender unit

The float can be cleaned up with the same cleaner used above. Hopefully, the float pivot will unseize with some penetrating oil and very gentle persuasion. New sender units and floats (plastic - ugh!) are available at the time of writing (2017). I made a Viton gasket for it, to replace the original cork item, to improve resistance to fuel with ethanol in it. The fixing screws (6 of them) are 3BA x 3/8", making it a little harder than usual to find replacements. I replaced the steel screws with brass ones.

Painting the outside

The 80/20 solder coating doesn't present any problems for painting. You can treat it with that same phosphoric acid solution prior to applying your preferred painting system. In my case, it was epoxy mastic followed by 2-part polyurethane. The tank should be given the best protection to guard against external damage or deterioration. I didn't top-coat the filler pipe, because this will be flock sprayed (as original) to match the boot.

I was already aware of a tiny leakage where the filler pipe is soldered to the tank - fortunately near the top of that pipe. This could be clearly seen while cleaning the inside of the tank, since some cleaner seeped out of a pin-hole in the solder join. Rather than try and use epoxy tank repair material, I thought I might as well rely on the epoxy-mastic that was going onto the tank anyway. It is thin enough to work into any such tiny hole. I'll monitor it for any leakage in service.

Finally, the hessian padding can be stuck on with paint. This padding cushions the tank against the aluminium frame that helps to support it.


Fitting the tank back into the car looks straight-forward, but can take some time. With the hessian padding, it is a tight fit in the aluminium support frame. The nuts at the front of the tank, allow you to adjust the tank's position until the top mountings line up. There may be some plywood packing pieces to refit, before the 2 coach-bolts go back in.

Update: Although the 4 bolts at the front of the tank are made long - so that you can pull the tank into the support frame - I would not recommend installing this way. It places a lot of stress on the aluminium rivets holding the steel brackets onto the aluminium frame (although you could always change these for steel rivets?). Instead, persuade the tank and frame to come together with a soft mallet and some wrestling with your hands! After it is installed, those little rivets are unlikely to be placed under much stress.

Above is one of the front brackets for the fuel
tank with the long bolt welded to the tank.

When I refitted the outlet pipe, I could not screw in the 90 degree bend, because the damper subframe obstructed it as I turned it. Since the end of the pipe had not been cut square, I filed it square, which gave the needed clearance. The damper subframe had been a later addition to this early AC. The coupler hose for the filler, is a standard length, 75mm. Inside diameter is 60mm, with a wall thickness of 4.5mm. It is reinforced and it would seem prudent to obtain one that can resist modern fuel, although it might be hard to find hose of such large diameter? The fibre washer for the filler cap can also be renewed, but I'll make a new one out of Viton rubber.


A problem for classic cars that are not used frequently, is that varnish forms in the fuel tank and system, and this leads to blockages. Condensation in the tank might also lead to corrosion. There are additives available to reduce this problem, although I can't give any first-hand experience of how effective they are.

Fuel line

Above is the original copper pipe resting on a coil of new copper-nickel alloy pipe.

The original pipe connecting the tank to the filter was made of copper (5/16" outside diameter). To remove it, you have to straighten out the rear end and slide it through the chassis and out of the engine bay. Installing it, involves bending the end of the pipe again. This work-hardens it and increases the risk of fracture. Therefore, I made a new pipe, but used copper-nickel alloy piping which is less likely to crack and is more resistant to corrosion.

The rear of the pipe has a soldered connector with a 1/4BSP coupling nut. Needless to say, you don't want this to leak fuel and so it should be fabricated with care. Clean the surfaces with abrasives just before soldering. I gave a final clean with some meths. Then apply a suitable flux paste to the area where you want the solder to flow. Slide the coupling nut on, then the connector and heat with a small blow-torch until hot enough for plumber's solder to melt against the metal (keeping the solder out of the flame). When it has cooled down, clean off the excess flux with meths. Then pressure test the pipe. I applied a tyre pump to the front end of the pipe. The rear end was submerged in water with my finger over the pipe end. All very hi-tech! No bubbles came out of the joint.

The length of my original pipe was 118 inches (3 metres). I made the new one 2 inches longer to increase the amount of bends at the rear. The extra bends give some springiness to allow for movement of the tank without stressing the pipe connections. The extra length made it easier for me to experiment by adding a valve (see below), but still be able to remove the valve without putting more permanent bends in the pipe. The pipe will be longer if you have the later car with the filter mounted higher on the bulkhead, above the pump.

The front end of the pipe has an olive and compression nut. Surprisingly, the pipe threads on the filter are not BSP... or UNF or BSF, and are finer than any of them! A small fraction smaller in diameter than 1/4BSP. 1/2 inch diameter and 24 threads-per-inch, and appear to be of Whitworth threadform. So, I re-used the original coupling nuts.

The new pipe can be threaded into the chassis just ahead of the bulkhead. Towards the rear of the chassis, it has to pass above the tubular cross-member within the box section, and then re-emerge. A brass P-clip secures it to the wooden sillboard, with a sheet of thin rubber to prevent it rubbing against the chassis. There were originally 2 steel spring clips to hold it inside the chassis channel, but these tend to pop out (as well as rusting). So, I made new brass P-clips to bolt on and lined the clips with heavy-duty sticky-tape. For the front one, I added a rubber block to raise the pipe. Originally, the elbow pipe under the tank pointed to the left of the car, and required a tight bend in the main pipe. Depending on the thickness of the 2 fibre washers (plus sealant) under the tank, the elbow can be made to point more rearwards which is more convenient.

Above is the tank outlet with filter gauze (3/4 BSP tread) and the elbow pipe (1/4 BSP threads).

If the car is dismantled for restoration, make sure the pipe will not obstruct any parts that will go on later. At the front, there is a tight clearance for the ignition coil. At the rear, it needs to clear the back seat, and also the axle and spring at maximum deflection.

It is worth applying non-setting gasket sealant to the threads on each fuel connection. I used to use Golden Hermatite some years ago, and now use Hylomar Blue. Don't use PTFE plumber's tape for fuel systems.

Above can be seen the back of the valve I added under the tank.

Fuel Filter

AC used a British made Zenith filter. Internally, it has a stack of flat brass washers that are quite robust and can be cleaned when necessary. The glass sediment bowl, causes the fuel velocity to reduce, allowing anything heavier than the fuel to sink and be trapped. That might be solid debris or water. With alcohol added to petrol, and thus more risk of water separating, the bottom exit tank helps to remove any water which can be caught by the filter bowl.

The sealing ring for the bowl is a typical cork/rubber gasket. I made a new one from 1mm sheet Viton to be sure it will stand up to modern fuel. The ring size is 44mm OD and 36mm ID.

There seem to have been a great many makes and models of filter on contemporary makes of car. Most of the new ones on the market are larger AC Delco units with UNF threads. Land Rovers, and some commercial vehicles, have a tap built in to the filter, making maintenance easier.

An old filter will be covered in varnish and gum deposits. I soaked mine in POR-15 metal cleaner for a couple of days, and sprayed the threads with penetrating oil to dissolve gum. I cut out a rubber mounting pad from 6mm thick natural rubber.

Adding a fuel cut-off valve?

This is still experimental at the time of writing (2020). With a bottom exit tank, any fuel leak will empty the entire tank contents. Early 2 Litre ACs have a low mounted filter on the bulkhead, below tank level. That means you can't remove the pipe end, or filter bowl, unless the front of the car is jacked up (or parked facing up hill).

I decided to experiment with a valve under the tank. I considered an electric solenoid valve, but most of these need well filtered fuel to avoid clogging up the valve. They also draw over 1 amp in current continuously. I have fitted a competition style manual shut-off valve which only turns 45 degrees to close it fully. I chose a metal unit with a ball-valve in a PTFE seal (which resists most liquids), and a 10mm aperture. That should be more than large enough. It also has 1/4BSP internal threads, so it screwed straight onto the existing elbow pipe under the tank. I bought an additional union to connect it to the main fuel pipe.

Having made a new plywood partition for the boot (trunk), I have cut out a hatch for quick access to the fuel valve. I've fastened the hatch with 2 magnetic catches, rather than having it hinged. But, I've attached a hinge to use as a handle which, hopefully, won't get damaged by luggage.

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Website started 29th December 2006