The Tale of an Aluminum Rear Lid

[GeorgeK]

I love aluminum lids. The idea is so simple, yet so effective in shedding weight, and at the same time so seldom used by Porsche on the 911, it ticks all the boxes I like. Light, simple, efficient and rare.

I have had a front and a rear lid in the past, that were on my Orange Carrera 3.o that some will remember. I also have a front lid off a 1991 964 Cup, predating the alloy lid of the 964 RS. That one has been hanging on a ceiling longer than I want to know...

Enter Ebay classifieds, a german branch of eBay for local deals, usually without shipping or with local shipping. I peruse it from time to time, some good deals to be found.
I had an eye on an alloy rear lid (for the record, 2.2 S and E, 1970-1971) that would not sell, because it was damaged by the latch, obviously visible from the pics on the ad.

[GeorgeK]

I messaged the seller about it. After a bit of back and forth, we reached a price that suited both of us, less than the original asking, since there is (quite) some work to be done on it.

Of course, the agreement also included no shipping. A hassle for the seller, and a risk for such a fragile, old rare part.

So, road trip. 470 miles north to Cologne, with my 11 year old son for company, and to give him a taste of what we did with his mom before he was born. He loved every minute of the trip up north, even the part where the fuse for the fuel pump *melted* in it socket, leading to a 1 hour roadside repair with a swiss army knife and the car's tool roll.

Once we got home, a quick clean revealed what I have to deal with:











So busted central rib by the latch, corroded and broken, with a repair consisting of steel plate and a boatload of pop rivets. The other end by the grille frame had the decency to let go of the factory welds without further damage. The frame by the license lights is also slightly cracked, but is surprisingly stiff considering.

But there is more. The astute here will have noticed that the lid is smooth outside, but has pop rivets on the back side where the holes for the 911S (or E) and the Porsche script letters are on a vintage rear lid. That means the pop rivets were put in from the outside then hammered below lever and bondoed smooth. Oh boy...

[Knockdown]

Pinky light, nice!

[GeorgeK]

So, I need a plan. This rib must be repaired, no question. Maybe it can be welded? My body shop of choice welds aluminum, since they are one of the few shops That Audi brings their alloy bodied cars to.
But no. The aluminum is so thin, weakened by endless flexing and corrosion, there is no longer enough material to weld.
I need to take this rib out, to assess it correctly, without damaging the rest of the structure. 47+ years have done most of the work for me, with broken welds everywhere. A few rivets to drill, and...nothing. The rib is also welded to the inner frame, exactly between the license plate lights. Hmmm.... Enter paint stripper, on the supposed area of the welds. Bingo. 3 small visible depressions, that are easily drilled out with a 6mm bit, and the rib falls out.

[GeorgeK]

So......
Crap. That piece is not salvageable. No way no how.

After sudying it, I realised that while it looks like a rather simple folded sheet, it is in fact not made with straight folds, has progressive depth and curved parts. A stamping.

I decided to make the part. First step is to create a buck over which I can hammer/shape aluminum sheet. Calipers, pencil, scrap wood, file, saw, and I got a reasonable buck of the general shape, minus the lower/rearmost end, that goes in the inner frame of the lid.

[reachme]

beginning of a great story. inspiring me to write my tragedy about a horizontal seat motor.
can't wait to see how this ends

[GeorgeK]

I have had that set of bodywork hammers/dollies for a few years, bought them at some shop sale thinking they could be of use someday, That day is today.

Measured the original rib at.85mm, with paint, so the .8mm aluminum sheet available at the local shop should do it. scribed the middle line, drilled twice where the large holes are on the original part and screwed it to the wodden buck.

Have I said that I suffer from a rather chronic epicondylitis (tennis elbow, except I don't play tennis)? I feel a flareup and Ibuprofen in my near future. Ear muffs are a must.

[RDM]

Man, this is a mess!

Where are you located, 470 miles south of Cologne? Italy? The South of France?

I only had to go 150 miles north to Cologne for my Cerakote applier.

You've got a fascinating story going on.

[GeorgeK]

Swiss Alps

[RDM]

Nice. We try to make it to Interlaken every few years, but not this year. If you make the journey again and need a way-station, let me know.

[chrisbalich]

great work! excited to see this fully sorted.

[30westrob]

We hope to see your progress, and of course the final product in the future. Rob

[dafischer]

Nice work! I'm always amazed at the ability and determination of we Pelicans.

[Trackrash]

Nice work. Great documentation and a wonderful motivating project.

I have done fabrications in steel and fiberglass, but aluminum? Bravo!

[adias]

Great project! Where did you store the lid on your trip back? Behind the front seats? Do you have a photo?

[GeorgeK]

Adias, I could not go with a 911. The C4 is in 1000 pieces post repaint, and the cab has an unbalanceable front wheel that prevents highway driving (note: 15 inch dia. Pirelli P6000 become worse as they wear. Hard to balance when new? you'll never get them balanced after 15K miles). The sissy in me will also admit that 30+°c heat and traffic jams are no longer fun for 8 hours at a time. So MB 280 TE it was.

Back at it. Cutting to shape and forming the end.
Cutting to shape was no challenge. Lay the broken part on top, scribe a rough outline, cut 10mm too large, then trim as needed.
The rearmost part needed carful clamping in the vice and oh-so-soft hammering to get the fold and work the inevitable redundance flat. It is amazing how aluminum is malleable, given enough time and finesse.
Then it is try fit, adjust a tiny bit, repeat a hundred times. In the end the part fits, doesn't bind or stress the frame or fall out by itself.

I purposedly did not cut the 2 large openings in the center rib. First they are there to allow attaching the badges, which will no longer be there, second they weaken the part significantly, witness the lergest crack right through the opening.

This is where I am now. Next is to strip paint in strategic places and see about those blind rivets. Next installment when time permits.

[mb911]

Looks like its getting there.. What is your plan for dealing with all the tool marks?

[GeorgeK]

Hi Ben,
Tool marks are beyond my capacity, but if you have a way, I am all ears. I figure since it is not visible, they won't matter so much, plus I get some pride in seeing that it was hand made.

Today was a start at stripping and rivet removal. By using a sharp wood chisel I managed to cut off the inner part of the pop rivets without damaging the alloy. I am relieved to see that the lid skin is not damaged otherwise. It was then a matter of punching the outer parts out, which revealed how much bondo there is, about 2.5mm in the worse spots.

I also stripped the inner frame by the license plate lights. A few years ago regulations changed, and the paint stripper available now is a weakish sauce that would hardly marinate your BBQ meat. I am in for a while with this.

Original lid color was viper or signal green. So if your early S or E has a missing lid, now you know...

[mb911]

Here are a couple thoughts and suggestions..

1st the orginal plan to weld would have worked well if you found someone at an airport that was a real avaition welder not just a guy that can weld. They would use a TIG machine versus MIG which is what the body shop you mentioned would likely do.

Second when forming parts especially aluminum you can form with wood versus steel which you likely used. The execution of your buck and forming is fantastic its only the tool marks that are the issue. Now to get rid of them you could planish them out or if you want but not suggested would be to use file's and scotchbrite wheels on a die grinder..

Just suggestions as I teach fabrication at a local technical college.

[GeorgeK]

I did indeed use steel body hammers. I don't want to planish by sanding, as I don't want to remove material. I will scotchbite the piece to remove the sheen, and to allow for better paint adhesion.

As for welding, my body shop guys do alloy regularly, and know how to weld it correctly. Aston, Ferrari and Audi are there regularly. I guess they have the correct setup, but I'll ask them.
Keep suggestions coming, I'm all ears.