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Old 09-09-2018, 11:54 AM
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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 3)

For the fuel level sending unit and in-tank fuel pump I decided to use thick flanges with blind holes for the mounting screws. By blind holes, I mean the holes don’t go all the way through the flange and thus the fasteners won’t be a source for potential fuel leakage. I came to this decision after consulting with an engineer at Aeromotive which is a maker of aftermarket fuel system components. Given I plan to use an 8 stack EFI on the Miura’s engine, I wanted to use an in-tank fuel pump. Aeromotive makes a real nice universal in-tank pump unit, called Phantom, made to be retrofit into “any” fuel tank.

Given the unique/odd shape of this Miura’s fuel tank, I decided it would be best to confirm with Aeromotive that the 3 ¼” hole needed for their pump unit could be effectively sealed and thus wouldn’t seep fuel. I wanted to install the pump near the back of the tank to ensure fuel would naturally move to it during hard, extended acceleration. So that means it will be in the short part of the tank and there can be up to 12 inches of “head pressure” on the flange seal when the tank is full.

The engineer thought their “as designed” seal would hold fine but suggested a custom weld-in flange with blind holes and an “O” ring seal out of an abundance of caution. My rule of thumb whenever dealing with flammable stuff, always proceed with an abundance of caution. So I decided it would be worth the effort to make custom flanges. In addition, it would give me a non-trivial project to try out on the metal lathe I had recently acquired, so all the incentive I needed. Please note, I’m a newbie machinist so there might be better ways than the below to go about making the flanges.

I don’t have any large diameter aluminum round stock on hand so I decided to make the fuel pump flange from ¾” thick billet and fuel level sensor flange from 5/8”. I measured the lathe chuck and determined I needed a 1.5” hole in order to chuck up the metal. I started by cutting out a square of metal and using my milling machine to bore the 1.5” hole in the center.



I then cut the corners off with a band saw to make it near round and proceeded with machining operations on the lathe to turn the outside and inside surfaces to size. Here it’s being prepared for turning the groove to hold an Oring. Given my lack of experience with a lathe, I took things slowly and it took about a day’s worth of my time to complete the 2 flanges.



Next was fitting and welding the flanges to the tank. I had selected a “tube type” fuel level sensor to minimize the gauge needle movement from fuel slosh. The “full” reading will never be accurate given the odd tank size (i.e. gauge will read full until top part of tank is emptied) but the vertical positioning is important in getting an accurate “empty” reading, which is the more important of the two in my opinion. The flange and sensor were trial fit in the tank to determine how far down to insert the flange such that the sensor tube would be at the bottom of the tank prior to welding.



For the fuel pump flange, vertical positioning isn’t critical as the fuel pump itself is adjustable in height. So I positioned the flange just through the sheet metal where it would be easiest to weld.





Well I’m now blocked waiting for the bead roller motor in order proceed further with the fuel tank. More to come as the fuel tank construction progresses…
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