Section XV Fuel Tank and Boot

Warning:- Before carrying out any modifications to the standard design seek written approval from the Kit Designer. Use only high quality materials and fasteners and lock all threads. This applies particularly to Safety Critical items such as Brakes, Steering and Suspension Components.

After some thought I have decided to have a semi fixed cover over the top area behind the seats under the roll bar, and to put a small boot with access from inside the car behind the seats. This is a similar design to that of early Austin Healy Sprites, with no external hinged boot lid at all. See section on fitting the Seat Rear Panel.

Route all pipes and wires before you fit the boot. If you intend to fix the boot permanently at this stage you are advised to sort out the rear brake pipes and the 3 way brake fluid union as they exit the propshaft tunnel under the boot floor, as does the wiring loom and twin fuel pipes. Access will be virtually impossible later without removing the boot.

Boot.

The rear seat panel is faced on the back with a large piece of 10mm exterior grade ply secured with at least 6 C'sk screws, these screws pass through the ply into the boot vertical side battens. The panel has a rectangular hole cut out to suit the hole in the stainless panel giving access to the boot. This at least gets rid of the Sierra tank cut out and stiffens up the rear sheet panel considerably. The boot itself is built up using 10mm ply and 25mm x 20mm softwood battens, screwed but not glued. You may need to remove the boot at some time in the future so it needs to be semi -permanent. The floor of the boot sits on the chassis and goes back as far as the tank, giving a boot approx. 40mm high, 710mm wide and 40mm deep. Any bigger items will have go in the passenger footwell or on a rack. This is a sports car not a lorry. The sides and back are vertical with the top sloped to match the outer top cover. The boot sides and floor are secured to the seat back panel, and the floor is also screwed to the chassis. All the ply is double varnished and joints sealed with silicone mastic. Note the angle plates on the top corners. The insides are covered in plain black carpet. When the outer top is finally fitted it will be tack glued to this top face to prevent drumming. Do not be tempted to use chipboard or MDF it will fall to pieces in no time due to the damp. Once the boot is in we can turn to the fuel tank.

Fuel Tank.

The small fuel tank supplied for the 2B, when dropped into the only possible location, is just a couple of inches short, to sit nicely between the rear vertical chassis tubes. It also lies at an angle of 17 degs to the horizontal. This means that the Sierra fuel gauge sender arm does not hang vertically. If you have yet to buy a tank an improved design is suggested. There are endless ways of securing the tank, which if the tank cannot move, are all just as good as the next. The photographs show my solution, but you may care to improve on this. The sender, wiring, delivery pipes and filler can all be addressed later. The boot does in fact form an integral part of the fuel tank fixing, as the fuel tank top front rests on the boot floor's rear edge, which has been made just wide enough to fit between the end flanges of the short tank. The front bottom edge of the tank sits on a piece of 20mm stainless steel angle secured to the chassis at the correct angle by a couple of trunnion plates. The tank is insulated from the angle by a piece of webbing or similar hard rubber material. The outer rear edges of the tank are wedged tight into the chassis vertical tubes with two pieces of wood, secured to the chassis/tank with structural adhesive. The whole lot is strapped down secure with two rigging screws and 4 stranded wire loops. Two are looped around the lower chassis tubes and two are secured to the boot floor. These are then tensioned with the rigging screws. This gives a very secure simple and cheap fitting. To avoid any possibility of the wire loops rubbing on the tank, a piece of 1/8" marine ply, well varnished, is slipped down between the tank and the wires. The lower edge of this panel conveniently rests on the lower flange of the rear panel. The tank is electrically insulated from the chassis so an earthing strap will be required.

Fuel Tank Filler.

After you have fitted the Fuel Tank and the Rear Panel the Fuel Filler flap and neck can be fitted. The kit comes with a very nice lockable "Aero" style unit (a lockable flap is now mandatory for the SVA) The filler neck supplied was clearly of an incorrect design and was never going to fit. Much to their credit RHSC's replaced it without any fuss, despite the fact that the kit was 16 months old. In the event I decided to stick with my original idea. For those of you who may be building from a second hand kit, or refurbishing an older car, another design is offered. By careful cutting and re-welding, all of the old pipe was utilized, but not the flange. Note the small catch plate fitted inside the top front of the filler neck so that the locking flap actually locks. (see also the additional technical information supplied with the original kit) There are details of all these modified bits in Appendix II Link to AutoCAD Drawings No doubt builders will find other (better) solutions that may involve less butchering and welding. To ensure that the pipes were cut and welded correctly, a wire model was first made, and a dummy rear panel/fuel tank made in 20mm chipboard. The unit was tack welded up in this "jig" to ensure a perfect fit. See the photographs. Use the AutoCAD drawings as a guide, as all cars will vary to some degree. The amount of work involved in this filler was unbelievable, probably not worth it. But it does give a very secure, leak and fume free job, which will never be seen !!

To avoid static sparks the delivery system and tank need to be fully chassis earthed.

Sierra Sender unit. (Fuel Gauge Rheostat - Fuel delivery and Return pipes)

The sender unit was rusted very badly so a new base plate was manufactured from a disc of brass sheet. The old unit was stripped, then reassembled onto the brass disc, mainly by soft soldering. This had 4 holes drilled to match the weld studs on the tank, (which are NOT symmetrical) and was bolted down with a cork gasket and sealant. The fuel pipes were connected and clipped to the rear of the boot. Note:- The output signal from the sender rheostat must be insulated from the tank. Do this with care as a spark or short could cause an explosion. Note also the tank needs an earth strap. Note that new units are available for about £15.00.

Fuel Pick Up and Gauge.

The Donor Sierra fuel tank is quite a shallow unit, sitting as it does under the boot floor. The RH tank is quite narrow and deep. This means that the Sierra pick up pipe only extends about 3/4 of the way down the tank. This is fairly simple to remedy. First measure accurately the depth of the RH tank from the gasket face to the bottom. (250mm) Now measure from the gasket face on the sender to the end of the filter.(210mm) So we have a useful 40mm at least. As the tank slopes at 20 degs if we can arrange to sit the filter into the lower corner of the tank we can get quite a bit more. Cut about 40mm off the end of the delivery pipe and solder on a sleeve to increase the length by 40mm. Re-fit the filter. Make sure the gauge float is free. Any air leaks will cause poor fuel delivery as the tank empties. The same applies to the float on the sender, which if not corrected in a similar way will register empty when the tank is in fact still 3/4 full. The float moves thro' 90 degs full to empty. The wire will need to be lengthened by about 50mm but cranked down so that the TOP of the float, when fully up on the top stop, is about 5mm ABOVE the tank top.

A second option, the one I have used, is to remove the filter altogether and fit a long curved plastic pipe that fits snug into the lower corner of the tank. This ensures that every last drop of fuel can be used, the tank is small enough as it is. As a precaution I have fitted an in-line filter which can at least be cleaned now and then. A blocked filter inside the tank is not so easy to clean.

It is always a good idea to test the completed set up by running the tank dry and noting the gauge reading. How many miles will the car do on a FULL tank, how many miles will it do after the gauge shows empty, or more importantly, at what point on the gauge does the car STOP. Do not forget to carry a gallon of fuel to get you to a petrol station when doing these tests. Note the Stainless Steel used for the tank is magnetic, it is a good tip to attach a magnet outside the lowest part of the tank, under the hole for the sender, any swarf etc. will eventually attach itself to the magnet where it can eventually be removed.

Spare Wheel Carrier.

Warning:- When you drill the 4 holes for the Carrier, put a piece of wood between the tank and the rear panel, otherwise you may through drill into the fuel tank

Now is a good time to fit the spare wheel carrier. Full details are given in Appendix II Link to AutoCAD Drawings of a suitable design. Bolt the carrier to the car with 10mm stainless steel bolts and nylock nuts. Drill the 4 holes in the correct position with the new wheel and tyre as a guide. Use a 170mm sq. 2.5mm stainless steel plate and a piece of 9mm ply approx. 300mm sq. on the inside and bolt the lot up very tight. Put some No-Nails glue on the ply panel inner face. The spare is simply bolted to the carrier with 4 suitable bolts. Note:- If you intend to use 4 RHSC's chrome wheel nuts (standard Sierra threads) these are 12mm x 1.5mm pitch which is a non-standard metric fine thread. (Standard is 1.75mm) I suggest using 4 wheel studs knocked out of a Sierra hub. If you secure these studs permanently to the carrier, you may find it impossible to get the spare on or off, (6.5 J wheels only) as you cannot pull the spare wheel forward far enough to clear the studs. To get around this, but still use the studs, I made 4 false hex heads for the studs and pressed these onto the splines. Any protruding splines were turned off to 0.500" dia. You will however need two spanners to get the spare off, but this may usefully deter any thief. Fortunately you do not have to use the spare very often. Whilst on this point, do not forget to carry a Jack that will lift a Robin Hood (very low ground clearance and no jacking points) and carry some tools. You may also need some other form of anti-theft device for the spare, such as a chain or a fancy nut. (A wheel and tyre is worth at least £130.00) The number plate wires are routed through the carrier centre hole inside a 10mm dia plastic tube for insulation. See photographs of the finished unit below. Welding note:- If you do decide to make the carrier as above, bolt and clamp the two flanges to a couple of flat 3/4" plates, otherwise they will distort badly when welded due to heat and fillet shrink etc. Note that the Tyre and Wheel are required to fit the SVA radii requirements so a Tyre/Wheel cover will be required. A hardboard disc to fit into the wheel rim was also suggested. My car failed on this point as I had no cover. See Section XXV The SVA Test.

Ride Height.

Unless you have already done so, you will need to set the rear ride height. I did mine as follows:-

Fully fit the Rear Coil Overs and with the Seats, Fuel and Two adults measure the height of the units from the Swinging Arms to the underside of the uncut tube ends. ie. With the shocks in a loaded state. Jack up the car on the chassis and remove the units. Then with the same set up and the car on two jacks, adjust the height until the wheels are vertical and the drive shafts are at a slight positive angle. Say 1 to 2 degs, (high at the diff) Measure the swinging arm to tube dimension as before. The difference is the amount to cut off. Since this process is more or less non-reversible, measure twice and cut once. You can always cut more off later, but you can't put it back on. As a guide mine came out at 45mm per side. The main Chassis lower tubes will be approx. 7.5" off the ground.

See the attached photographs for details of boot construction etc.

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© Colin Usher 2005