Fuel Tank

Shifting focus away from the brake lines, I decided to tackle the fuel tank next. I purchased this at the same time as my original kit order. Since its arrival, to save space in the garage the tank has been sitting in its correct location within the chassis, all be it with its tabs resting on the top of the chassis. Although the tank fits perfectly in this position, the manual states that these tabs should be on fastened to the bottom of the chassis rail (not the top). This creates a flat surface between the fuel tank and chassis rail for the boot floor to rest on. To achieve this fitment, we require some bolts holes to be drilled into the tanks mounting tabs and the chassis.

There does however appear to be two schools of thought around the best method to fasten the tank to the chassis:

• The factories (AK’s) suggestion is to drill holes in the fuel tank tabs, and then drill and tap a corresponding holes in the chassis which M8 bolts can be fastened to.
• Alternatively, some builders have proposed securing these fuel tank tabs with strips of metal held in place either side of the tab by M8 rivnuts.

The main motivation for the alternative method is the concern that the chassis rail is too thin to support an M8 bolt. However, I believe from memory that as part of the Gen 3 being nicknamed the ‘super-light’, it uses a thinner gauge steel for the chassis than the Gen 2 chassis (which I have). Therefore, at least for now, I will stick with AK’s method for securing the tank, although I may later add some extra metal straps to some of the fuel tank tabs.

Making holes in the tabs

The first step is to mark and drill holes in each of the 5 fuel tank tabs. These need to be drilled in the center of the tab and in chassis rail. I began by mocking up the location of the fuel tank in its correct location (from the top) within the chassis. To record this location, I placed masking tape around the edges of where the fuel tank tabs met the chassis.  As the chassis rail and fuel tank tabs are about the same width, I only need to determine the center point of the tabs. With a ruler and sharpie this is an easy job.

Fuel tank sitting in chassis with marked center of tabs marked.

To avoid the drill bit from walking, a center punch is used to create a small indent. Then before drilling and to avoid damage to the top side of the chassis I raised all the tabs with some wood offcuts. You will notice there is some ‘rust’ appearing around the tank weld locations. I’m not sure how to deal with this, but I will be coming back to this later.  

Fuel tank tab, with the center marked and punched.

Its then a case of slowly drilling through the tabs, firstly with a 2 mm drill bit and then increasing with larger drill bits up to an 8 mm diameter. This is the first time I drilled into stainless steel and its surprisingly a lot hard and slower than plain steel.

Initial pilot hole drilled

With all the holes drilled out to 8 mm diameter the tank can then be placed directly back top of the chassis rail.

Hole drilled out to 8mm.

The tank then needs to be supported, with the tabs touching the underside of the chassis. For this I broke out my new (second hand) engine hoist and the trolley jack. With the tank it is correct location and lined up with the tape, the location of the corresponding holes can be marked.

Support the tank as I mark the location of corresponding holes.

As before a center punch mark is made before a gradual increase in drill bits from 2 mm up to 6.8 mm. This odd size of the drill bit is required to ensure there is sufficient metal for the coarse M8 (1.25 mm pitch) tap to cut through in order form the desired thread.

Tapping the thread into the chassis.

Tapped hole.

With this process repeated on all five of the fuel tank tabs, the hard part of this job is done. The tank can then be raised back into its slot and fastened in place

Fuel tank mounted to chassis.

I should also point out during this job I noticed that there were more signs of paint bubbling on the rear bar of the chassis. A quick sand down to remove the paint and rust was then followed by a spray with primer and black paint. Despite a slight disparity in the gloss level along this back bar, the repainted areas look good. I’m not too worried about this paint mismatch, as this area of the chassis is covered by the body.

Flush fitting tank.

That’s the fuel tank fitted for now. As I said at the start, I may decide to go back and add some metal straps to some of the tabs for extra support, but we will see.