Tuesday, January 9, 2018

Capturing an Escaped Captive... Nut

Rain. and cold. and blustery wind. All of my projects except one are sitting in the driveway under tarps held down with whatever I could get my hands on. My new-ish job has a policy about how much paid-time-off you can carry forward into the next year, so I find myself with days at home. So... what to do? Work on the one project that's sitting in the garage so one day it too can sit in the driveway under a tarp while one of his brothers are in the garage getting worked on. Today covers one of the final steps to achieving that goal.

Captive Nut
test fitting a panel
On the convertible MG, the top fabric is attached to a steel frame. Depending upon the year, the frame could take on one of a few forms. Mine is the last style, which folds straight back with large scissor-style hinges. These hinges mount to the sides of the car just behind the door latch. The steel inner body panel has a flat surface into which 3 holes were drilled at the factory. Inside the panel a nut was welded behind each hole. These nuts are what holds the convertible frame to the car, and therefore hold the top onto the car. Yes, there are clasps along the top of the windscreen and there are little hold-downs along the rear deck, but most of the work is handled by these 6 bolt-nut combinations.

The Escape
With any car, rust and wear take a toll. On the MGB, the little captive nuts (1/4 - 28) can detach from the inner body panel. Once separated, the frame can be attached, but the person doing the attaching must hold the nut with a wrench or pliers or something. Since the entire inner steel skin is usually covered with a vinyl panel (on top of which the convertible frame is usually attached), the owner has a choice: no more panels, no more top or re-capture the nuts. The PO had decided to select multiple options: no more panels and no more top, leaving the frame stripped of canvas and disconnected, but sitting behind the seats after discarding the vinyl cards prior to selling it to me.

I've driven around in plenty of cars which didn't have all of their inner panels. The operation of the car is in no way negatively impacted. It just looks trash. So, I decided I would get the nuts re-captured. There are a few ways to go after it.

Go Crazy, Tear down and Weld - Since these were originally welded into place at the factory before the body was assembled, getting them welded back in the same way is virtually impossible. I imagine someone industrious enough could take enough of the car apart to get access to the nuts. I don't see the value. Maybe if you have dreams of showing your car at concours or something, this would be the most-like-original path. Or maybe you're just sadistic. Either way, rock on.

Ugliest welds ever
Get a Repair Panel - Moss has a repair kit (link here) that could be used to fix this, so clearly this happens often. They run $18 each, which isn't bad, but as I noted at the beginning, I have some time, and I don't want to wait for shipping. I imagine the kit is a pretty easy solution though: set it so it is aligned with the holes, mark the mounting spot with a pen, drill, install. Easy peasy.

Make your Own Panel - While not necessarily the easiest, if you have some time and either don't have the money for the Moss panel, or don't want to wait for it, it's not that hard. I chose this path and I detailed steps below.

I have the nuts in hand and plenty of super-thin scrap steel lying around. I considered that the steel to which the nuts were attached did not need to be terribly stout. It just needed to be strong enough to hold the nuts in place against some modest pressure during installation. Once the bolts seat into the nuts, the plate doesn't contribute to holding the top on: its still the bolt-nut combination. With this in mind, I cut a couple (one per side) small pieces of HVAC sheet metal with tin shears to they fit in the hole, around the nut(s) which were still clinging to the inner body panel. I held them in place, marked the nut-holes with a pen and step-drilled holes large enough for the bolt to easily pass. I then sanded the steel to get any zinc coating off. This is important as the off-gassing from welding a zinc coating is really bad.

For some reason, my top had an extra bracket that looked like this, but not chromed. I think it is for a wind blocker (like this) that wasn't with the car when I bought it. Love that. Anyway, I took that bracket thing and used it to provide more meat for the next steps (see the top picture). I aligned the HVAC sheet with the holes in the bracket and then threaded the bolt through, tightening the nut against the HVAC sheet.  Next came some of the worst looking welds I have ever produced (see middle picture). That is saying something, because my welding skills are pretty bad. Still, I was able to get the nuts to hold to the sheet and hold well enough for me to remove and re-insert the bolts multiple times.
"Pop" goes the Rivet

Whether you did the Moss repair panel or you made your own, the mounting to the car is very similar. The panel sits flush against the outer-side of the inner wall (inside the cavity) with the nuts pointing out (away from the cabin). With the Moss panel, you can hold the thing on from the inside and see where the hole will be because it's symmetrical. Must be nice. With the home-made job, its not. Instead, I made judgments based on where the holes in the body were, and where the panel was as I held it up against the wall from inside the cavity. I marked 2 holes on the inner wall, pulled the panel aside and step-drilled to 13/32". This is just a hair larger than 3/8" so a 3/8" pop rivet will fit snug without binding as it goes in. To make sure I got the holes in exactly the right spots on the panel, I bolted it into place and drilled through the holes I'd just made in the body and then through the panel. With the panel still bolted on, I pop-riveted the panels in. I was still able to easily remove the bolts from the nuts (without touching the nuts), so the convertible top frame should now be capable of being installed after the interior cards are in place.

That's it for today's post. Yes, I could have simply ordered panels and this would have taken far less time. Instead, I got to play with my MIG and save myself about $40US. Thanks, as always for following along, and I hope you're having a wonderful holiday season. Hapy NewYear!

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