Fuel tank Installation

I have now moved on to install the stainless fuel tank from AK and a very nice part it is too. I've spent quite a lot of time reading various blogs etc. on how best to fit the tank ranging from drilling right through the chassis and welding in studs to straps that go under the tank and are fastened on top of the chassis. These are all great ideas but I have decided to go a different route.

On the AK Gen III chassis I believe that the tubing section has reduced from 3mm thick to 2mm thick (please correct if wrong but I'm going to be safe rather than sorry!). I would have been concerned simply tapping into 3mm thick with an 8mm thread which has a 1.25mm pitch doesn't leave many threads in the chassis tube. I have been known to be a little heavy handed when tightening up the screws so was worried about stripping a thread or two.

My solution was to make 5 off 3mm thk x 25mm wide stainless straps that go over the 5 mounting lugs welded to the tank. Rather than bolt through the luge and bolt directly into the chassis I have 2 bolts, one either side of the mounting lugs. These screw into M6 steel rivnuts.

I carefully offered up the fuel tank into the chassis, positioned it with an equal gap all round and marked the position each of the 5 mounting lugs onto tape that I have stuck on the chassis.

When all was suitably marked the tank was removed and the drilling process began. I had made a small drilling jig which I clamped to the chassis in the correct position and then initially drilled through with a 4mm drill followed by a cone drill easing out to the correct diameter. The cone drill was very much easier than using a much larger diameter drill in thin steel tube.

The only problem I had was that as soon as the 4mm drill broke through the chassis wall it snapped!!!! However, I was able to remove the broken part with pliers so no harm done. This would have been OK, I never break drills I thought to myself as the next one broke!!!. Chassis 2 me nil! The second drill end stayed inside the chassis and rang like a bell. This had to come out so I continued opening up the holes to 8.9mm (for the M6 rivnuts) and then used a combination of Henry the hoover, to suck out most of the drilling's and then a small powerful magnet on a string to get the broken drill bit out. This meant lowering the rear of the chassis and thumping the chassis with a rubber mallet to slowly make the broken drill migrate to the larger hole. 40 minutes of frustration and then joy as the broken bit attached to the magnet and came out the hole.

New plan was needed. I decided to use the jig only to spot the holes part way through then remove the jig and carefully finish. This generally took a little longer but gave much better results with no frustration.

The picture on the left shows the tank offered up with the lug located between the 2 rivnuts. The picture on the right shows it fully clamped up and nice and secure. In actual fact the strap evenly distributes the clamping load over the whole lug rather than just one bolt in the middle.

As you can see the tank in now installed. Not a permanent fix yet as I need to add sound deadening sheet to the large flat areas of the tank as it rings like the proverbial bell. Also I need to waxoyl the drilled chassis tubes. The 10 off  M6 screws will then be thread locked which will also seal the threads.

Only thing left to do is to add an earth strap from the tank to the chassis. I'll think about that later.

Next job is the brake pipes and fuel line.

Looking forward to the Bank holiday weekend as it is Stoneleigh Kit Car Show and I have lots of bits to collect. Lets hope for better weather this year than last.