install see-through panel in trunk floor (motor/engine view)

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Well-known member
Mar 5, 2013
Atlanta Georgia USA
An enterprising i3 owner in my area has installed a see-through panel in the bottom surface of the hatch/trunk area, so that he can show people what the motor / engine looks like. On our local Facebook group, I asked him to describe the modification and here is what he wrote.

He supplied some pictures but I haven't figured out how to post pictures here directly, and I'm not going to upload them to another site and then link to them here. Sorry.

Here's his writeup. My comments are in [brackets].


Basically, the window cannot support luggage or any with some weight since it's less than 1/8 in thick so I still need to use the carbon fiber cover that is removed. The cover is secured on top of the window by "locking" into place with new "screws" that I made. First step is to remove the 8 M5 screws (and save if you ever want to put back the cover). Purchase the following from Home Depot.

[he then posts a picture of a list of three parts]
- #10-32 x 3 inch machine screw [qty 8]
- steel T-nut, M5-0.8 [qty 8]
- acrylic sheet, 36 inch x 30 inch x 0.093 inch

[jargon: Plexiglass is a brand of acrylic material; Lexan is a brand of polycarbonate material; this page explains the differences and tradeoffs between them]

You will also need 8 #10 washers (not listed).

(see first reply below for comments on the 10-32 screw)

The acrylic sheet really just needs to be "cut" on one side along the 36" side. I believe it needs to be 24" by 36". The sheet can be scored and the snap off like cutting glass. Also, the corners will need to be cut because there are some rounded corners in the trunk. Use the cover as a template and drill eight hole in the window where the screws goes.

Next I had to make eight screws like this.

[shows picture of three things assembled together: T-nut, washer and screw without the head (see below)]

Cut each 3" #10 screws into two 1-1/4" pieces to get 8 screws. If you don't want to cut screws, I have seen hex screws that can also work. The key is no heads.

Also, you will need to flatten the prongs on the t-nut as shown.

[pic shows prongs bent down completely to make T-nut "washer" part pretty much flat]

Assemble t-nut and washer as shown. Temporarily add the #10 nut as shown. Note, m5 x .8 and #10-32 are close enough to work.

Make 7 more and use these "new" screws to hold the window in place. Just hand tighten the screws. If it is too tight you can ruin the neoprene nut underneath. Once hand tight, remove the nut on top.

Screw in place. Nut helps to hand tight.

Nut removed to allow cover to lock in.

Cover locked in

[answering a question about material] I thought about getting Lexan or even thicker acrylic so that I don't have to use the carbon fiber cover. But I wasn't sure how it would compare to the ribbed carbon fiber cover. Also I didn't know what the embedded metal strip was for, maybe some kind of shielding. So to be safe, I incorporated the cover into this mod by making those screws.
I asked him about the screw cutting. Why cut off the heads at all? Will the trim really not lay down if the
screwhead is left on? Cutting those off makes this little project a lot harder, and a little more risky (metal shavings are baaaad).

He answered:

The head needs to be cut off because it's too big to pass thru the cover. Once the 8 screws are installed, the only way to secure the cover is by having the screw pass thru the cover. If you don't want to cut the heads off, you could buy hex screws from Grainger. I couldn't find 1 1/4" hex screws either 10-32 or M5x.8 at HD.

Actually should clarify, the hex screw should be a set screw that uses the Allen Hex wrench. So instead of using the temporary nut, you could use the correct Allen wrench.
Here you go mrsmith :D
If you are a member of the BMW i3 group on Facebook, Bobby posted a full writeup here, with pictures:

Note that that is a CLOSED group, so you have to join it to see it. It's the end of the internet as we know it ...
ChrisC said:
Note that that is a CLOSED group, so you have to join it to see it. It's the end of the internet as we know it ...

Oh goodness, did you really have to bring that up again? ;)