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DIY: Spare tire well fuel cell cover

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Once I decided to go the fuel cell route in my 240z, one of my biggest concerns was what to do about all of the huge holes that would be left behind in the hatch area, not only simply for comfort (noise and air quality), but also to pass tech for autox/track events.  I enlisted the assistance of a fantastic fabricator buddy of mine (thanks Max!), and this is the (mostly) end result:

2015 06 10 20.56.56


For those just interested in pictures, the full album is here:


What we decided to do was cut a hole parallel to the hatch floor.  What this did was leave behind a nice perfect (70's-ish) circle, and wider recessed circular area where the cardboard cover sits.  Then the idea was to fashion a cover to essentially sit where the original cardboard sat, but fastened through the sheet metal in the hatch.


Of course, the next issue was figuring out how to create an access area for servicing the cell (feed, return, etc.), and more importantly refueling!  After searching high and low for over-sized fuel doors for trucks and other assorted applications, one day I was just staring into the hatch space trying to brain storm and I noticed the factory tool doors.  Perfect!  Not only is the opening big enough to fit your entire hand in, but they're wide enough to cover virtually all of the serviceable components of the cell!  I was able to find a used Z tool door quite easily off of eBay.


We then sourced a large enough piece of 18 gauge stock sheet metal to cut out a 27.5" diameter hole, and sent the stock and tool door off to a local waterjetting shop.  They were able to cut it to 27.5" diameter, and also cut a hole slightly under-sized for the inspection door:

2015 06 10 20.57.04


From here, I ordered 25 feet (15 would've been plenty, but I make mistakes and wanted extra) of X-1015 U-channel, for both the outer edge of the cover and the inner edge of the inspection hole:



We then drilled 8 holes for fasteners, 1/4" in from the outer edge (to sit dead center on the U-channel), and 22.5 degrees offset from center (of the front of the car, offset because of the chassis supports behind the diff and in front of the tail lights).  We also drilled 4 holes for the inspection cover:

2015 05 31 16.03.35

Then we placed the cover in the hatch, and drilled matching holes through the recessed area of the sheet metal.  From here, we slowly worked the trim around the outer edge of the cover:

2015 06 05 21.58.37


We then lifted the trim up at the edges just enough to locate a punch on top of the rubber, and punched out matching holes on the top and bottom of the trim, and also fitted the trim on the inner portion of the inspection hole.  From here, it was just a matter of placing the cover back in the hatch, lining up the fastener holes, and slowly working the fasteners down through the cover:

2015 06 05 22.30.34

Lastly, we had to fabricate tiny pieces of aluminum risers (~1/4") for the inspection door, to sit on top of the cover and below the hinges on the door.  This allowed the hinges to sit nearly flush, and most importantly allowed the door to be elevated just ever so slightly, so that the latching mechanism actually had tension against the U-channel rubber and would latch appropriately:

2015 06 05 23.37.00


As a happy coincidence, the new "3rd Z tool door" happens to sit almost dead centered with the factory ones, as the cell sits as far to the passenger side and as far forward (weight distribution) as possible:

2015 06 10 20.56.46


It could use another paint-job to try to clean up some of the flashing, but all in all I'm extremely happy with it.  It should be both air and water tight, and provides as-good sound dampening as the original spare tire well.



There's also the matter of all the original fuel hose holes (I can't believe it was even legal to run them into the hatch area, considering it isn't isolated from the driver's cabin).  I used this kit, which worked to plug up ALL of them, except for the original fill hole:



Picture for reference as the auction will inevitably end:

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For the original fuel fill hole, we'll just be making a small square cover, and using the original 3 bolt holes to fasten it down... and that should be that!


Please feel free to ask or PM me any questions, happy to help any Z owners to sort through this daunting task!


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Thanks all!  I've "borrowed" so many wonderful ideas from these forums, happy to contribute back in some fashion!  Another member, Zzeal, hooked me up with an exceptional deal on this:



I'll be honest, it's a _really_ tight fight.  Here's an album from the cell swap itself:


The pics aren't perfect; it's a bit hard to get good ones.  However, just beware that the dimensions are about as close as it gets across the board.  If I had to do it all over again, I'd probably opt for a 10 gallon to have more wiggle room.  The width is just perfect to locate it and still fit dual exhaust.  The depth is just perfect to be able to locate it between the diff and bumper, and the height is just perfect to leave enough room for AN fittings and braided steel (clearing the spare tire well cover) and sit ever so slightly above the diff and exhaust, at an angle.  It sits 5" off the ground on a fairly aggressive drop (5 3/4" off the rocker) with sectioned struts, and my region allows 4" at the lowest.  Coming off the trailer, I think 4.5" would be the lowest that would clear.  I got kind of lucky, measuring everything post-purchase.  :-)

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Nice work, I'm about to embark on this task myself. This gives me alot of direction of how to cover a giant hole. Is there any structural rigitidy lost by just fastening the piece instead of welding it in?

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The answer is most probably yes, but we're talking about 18 gauge 1970's sheet metal here.  Personally, I'm relying on my cage to pick up the slack.  :-)


My goal was more air, fuel, and water-proofing it, and this succeeds in that department.  Also, welding it completely takes proper servicing out of the equation without fully dropping the entire cell, which by the way gets veerrryyy interesting with no access from the top.

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Nice set up btw. I am getting to the point where instead of spending $500 on coating my stock fuel tank I think I might do a fuel cell.


With that said, did you custom fabricate the bar that looks like it bolted to a stock location? How much did you have to cut in order to make this fit?


Thanks ahead of time for you help.

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Unfortunately there's nothing underneath the factory setup that you can just bolt to. What I did was use two pieces of bar stock, which I drilled to attach to the front and rear of the cell, then attached them to the car with 4 angle brackets (one on each corner), which were welded to the frame rails / chassis.


You can get a bit of an idea with some of the pictures found here:



It really wasn't that hard.  Everything used to mount the cell itself I bought from Home Depot.  I'd argue that I spent more time taking precise measurements and mocking everything up than fabricating anything.  In the end, it was cutting 2 pieces of bar stock to the correct length, appropriately locating 7 holes on each (3 for the cell, 2 x 2 for the angle brackets), drilling 2 holes per angle bracket, then welding them up and attaching everything.  As far as the car itself, nothing was cut out other than the spare tire-well.  1.5 years and a handful of autox + track days later, and (knock on wood) no leaks, gas fumes, or fuel starvation!

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