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Old 09-05-2018, 03:31 PM
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heinke heinke is offline
MetalShaper of the Month Jan 2018
 
Join Date: Nov 2009
Location: Prescott, AZ
Posts: 487
Post Fuel tank construction (Part 1)

The fuel tank for this Miura is centrally located in the chassis, quite literally. It is located in the chassis backbone that’s between the seats and stretches from the cockpit front bulkhead to the rear firewall separating the mid-engine from the cockpit. The fuel tank is placed there so that the car’s front to rear weight balance doesn’t change as fuel is consumed from the tank.

Given this location, the tank has a very unique shape.



The tank is made from Al 5052 alloy in .063 thickness. The aluminum sheet was cut on the same CNC router table as the chassis using tabs and slots to index the pieces. It has two internal baffles to help control fuel slosh during acceleration and braking. Given the high level of precision for the cuts and bends, the un-welded tank holds its basic shape with just a few pieces of masking tape.

I decided to trial fit the fuel tank to the chassis prior to welding the sheets together. The tall part of the tank is located up front just forward of the windshield bottom. When I installed the cowl/windshield in the chassis, the wiper motor needed to be removed due to interference with the chassis. So I knew the chassis backbone needed an alteration for wiper motor clearance and I suspected some additional clearance might also be needed in the fuel tank. I cut away the ¼” thick aluminum in the backbone until the wiper motor could be wiggled into place and bolted down.



The backbone top cover was also cut and additional bends put in it until it cleared as well. The fuel tank was then raised in place. The good news is that chassis backbone fits to the fuel tank like a glove, so fuel capacity is maximized. The bad news is that a small alteration is needed in the fuel tank for wiper motor clearance. The interference area is small, so only a small change was needed. I made ½” cuts about 1.5” apart and folded the metal over 45 degrees to make an angled edge where it was a square edge prior. With this, the wiper motor now clears both the backbone and fuel tank. Note, I also had to carve a half round shape out of the pedal mounting plate for clearance.



I decided to bead roll some “stiffening ribs” into the sides of the tank. I did this to minimize the chance of vibration that might occur in the tank walls when the fuel level is on the lower side. I used a 5/8” wide half round bead roll for this.



Unfortunately, the electric motor on my bead roller died before I was able to finish putting in the beads. I took the gear box portion apart and found one of the motor bushings had been obliterated causing the failure. I’ve been thinking about upgrading to the “industrial strength” motor for a few years and now I’ve got the motivation.

More to come as the fuel tank construction progresses…
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