Fuel Tank Sending Unit Studs

[specracer]

Im working on a car that hasn't moved in 5+ years, and part of getting it going, is tank cleaning. The tank is in overall decent condition, but was gross inside. So part of the effort, was to remove the sending unit. I soaked the studs with penetrating oil for a few days, and would normally use heat to free these nuts, but

tank was not free of vapors yet, so no heat, and I didn't yet know the sending unit was junk. With all this, I was still very patient, just barely breaking the nuts free and working them back and forth to get them off slowly. Got all but one off. It broke off the stud.

Is the stud able to be pressed or threaded out of the tank? If not, has anyone come up with a solution to a broken stud? And if parts are needed, maybe a recommended source?

Thanks

[ja17]

I think the studs are welded in place during the manufacturing process. Most likely four will work with a new gasket. Otherwise it is a tough fix.  If you must repair it most likely the tank will have to be removed, the broken stud drilled out and another stud brazed or welded in place. You can get a used stud from a bad tank from someone on this forum most likely.

[specracer]

That is exactly what I figured was the case. Thank you for the reply.

[mistertj]

All is not lost. Will take a couple of photos and send along with how to fix later today. With the fix I'm thinking of, tank need not be removed.

[mistertj]

Assuming that you have the fuel sending unit out of the car, take it to the hardware store to fit and purchase what I think is called a tension pin, I called them curl pins but many do not recognize it by that name. In the photo I show two but they are not the correct size. The purpose of the tension pin is to help you locate the exact center of the broken stud so you can drill a pilot hole in it. While at the hardware store, purchase a screw that is of an appropriate thread and length to be the replacement stud. What we are going to do is drill out the old stud and then thread the hole for the new stud.
OK. now that you have the parts needed, take your vacuum cleaner hose (vacuum attached) and insert into the gas tank filler so that you can continuously remove any vapors from the tank and thus work safely. Next, need to tape over the tank hole vacated by the sending unit. Then need to grind the broken stud remains to almost even with the tank surface. Don't want to damage the tank sealing surface. Next, put washers on each of the tank studs and then (with tape removed) reinstall the sending unit. In the sending unit plate empty hole were the stud was, need to insert the tension pin. Needs to be a very tight fit. Since the pin is hollow, it provides a path to drill into the tank where the broken stud remains remain. With as large a drill bit as will fit into the tension pin center, very carefully drill into the stud...slow and steady is the trick. Once you drill through into the tank, stop drilling and remove the sending unit. Some very small metal cuttings may have fallen into the tank but they can be easily removed later with a magnet.
Now, just need enlarge the hole to the proper size so that it can be threaded (tapped) for the new stud. For the new stud, with the screw that you bought, you can leave the head on and screw up into the hole from inside the tank or you can cut the head off and screw the stud in from the tank topside. In either case, need to put a dob of something like JB Weld on the threads where they will touch the tank threads. Let cure overnight and you're done.
Any questions, just let me know.
p.s. My preference would be to insert the screw with head on up from inside the tank. It would make for a stronger fix. Still put a dob of JB Well or something like that up close to the screw (could be a bolt as well) head.

[doitwright]

Great description of the process by mistertj. But someone had to point this out. When you talk about "Then need to grind the broken stud remains to almost even with the tank surface." Reminds me of chapter 4 in the book about Max und Moritz, the two little German troublemakers. My mother made me read it when I was a kid. Still impacts all my decision making to this day.

[ja17]

Not sure it would be safe to use a vacuum cleaner in the tank, since the fumes would "evacuate" around the electric motor in the vacuum. I would drain the tank and use a compressor hose to blow the fumes out of the tank during the process. Might even re-fill the tank with water until the work is finished.

[mistertj]

Additional info. Since you said..."tank was not free of vapors yet"...I assumed that all liquid was gone, which I should have stated. My description assumes an empty tank where no liquid fuel remains.

[Benz Dr.]

I've seen guys run their car exhaust into an empty fuel tank to purge out any fumes. I can't say that I've tried it myself.

[Rick]

I do not take any chances with a fuel tank, even with old rotton fuel they can be very flammable.  It just isnt all that hard to remove the tank. If your has corrosion inside, that's the best way to do it anyway.

[Shvegel]

Not that I suggest this but I once watched a man torch and weld on the top of a 10,000 US gallon gasoline tank after draining it and filling it with water.  I brought out a 100# cylinder of CO2 and he laid that over the hole and cracked the valve.  When we got the bill he had listed a massage for “Stress Reduction” on it.  We paid in full.

[specracer]

This is exactly what Im planning on doing. Great write up. The roll pin to center is a great tip. The good news for me, tank is out, soaked a week or so with lacquer thinner (cuts the varnish), then another week with POR15 de greaser,  with a handful of larger nuts to roll around the tank helping free the rust. The tank is now clean and dry, and didn't need any acids to get there. Once I get this stud resolved it will be back in the car.

Now, just need enlarge the hole to the proper size so that it can be threaded (tapped) for the new stud. For the new stud,

[specracer]

As a follow up to close this out. The studs are actually attached to a ring, that is held in place with tabs bent over from the top. You can free this ring, but cant get it out, as it was installed before the tank halves were joined (our car is a 70 280SL). I did drill out and tap new threads, installed a new stud, and installed a new sending unit.  Success. Tank will go back in tomorrow.

Thanks for all the comments.