How to loosen a rusted nut/screw

Question

I have been trying the change the screws connecting the toilet tank, i managed to remove the tank but the nut it completely rusted and became one with the screw.

I tried holding the screw in place and rotating the nut to no luck. next i used WD-40 (sprayed it and left it for an hour then sprayed it again and left it for another hour with no luck).

I don't have access to a drill to drill out the screw top also i don't know if it may damage the porcelain which is the same reason i can't use a blow torch.

Is there a way to remove this without cutting it off ?

Update: I actually cannot drill the head off as to avoid any damage to the porcelain.

Update 2: Here are some images from the top-bottom view (sorry about things being dirty):

Answer 1

The most expedient and practical solution is to drill out the bolt. Probably access is better from the top through the tank, but it can be done from either side.

The goal of "drilling out" is to weaken the shaft of the bolt enough so that either the friction on the nut is reduced to the point where it turns, or the shaft breaks and separates into two pieces, both of which are easily removed.

Your concerns of damaging the porcelain indicate the choice of too large a drill bit. Choose a diameter smaller than the diameter of the bolt's shaft, preferably in the range 60 to 95%. If kept to the center of the shaft and parallel to it, the drill bit won't touch anything outside the bolt.

In the case of drilling from the top where the head is, drill into it about 6 mm/0.25 inches and then try turning the bolt. The head should break off and free both pieces.

Answer 2

Looks like the threads on the bolt are crushed/damaged, so you're only choice might be to drill it out or cut it off.

Put on a pair of good work gloves. Remove the blade from a hack saw. Then work the blade between the nut, and the plastic washer. It will likely be slow, hard work, but eventually you should be able to cut the bolt. Alternatively, you could try using a metal blade in an oscillating multi-tool or rotary tool.

Answer 3

while this problem was solved by OP, I'll offer another solution:

Take a die that matches the threads and cleanup the lower part of the threades. This is going to leave cruddy threads -- lots of the peaks of the threads will be smoothed off.

Take a pair of connecting nuts that match the thread. A connecting nut is just a nut that is aobut 3-4 thread diamters long. Used to connect chunks of threaded rod end to end.

Thread them both on, and get them about a nuts distance away from the problem nut.

Grab both connecting nuts with wrenches and tighten to each other. you want to jam them together putting lots of tension internally on the bolt.

Now grab the problem nut, and the connecting nut furthest from the problem nut, and try to undo the problem nut.

If you use a vice grip to hold the connecting nut, you can put a sock over the vicegrip, and let it turn freely until it hits the porcelain. This gives you two hands to work on the problem nut.

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Part 2: WD-40 is general purpose. There are compounds that are specfically designed to make removal of stuck bolts. Most DIY stores will have a selection. Stores catering more to mechanics may have a better selection.

Answer 4

Use an angle grinder with a cutting wheel on it.

Tape protection to the porcelain so that if you slip with the grinder you won't scar the porcelain. Heavy cardboard, or a wad of rags.

The grinder will produce sparks. Wear eye protection.

You likely have to remove the guard for this. Guards are mostly to proctect you if a grinding wheel disintigrates. Cutting wheels are reenforced with fiberglass and I've yet to see one fly to pieces. At worst they send a small piece off that hurts if it hits. Hence eye protection.

Slice the bolt at the washer. This will scar the washer. You may have to replace the washer.

Take your time. It's an awkward position. Stop and rest when your arms ache. Twisting may cause the wheel to bind which can break the wheel. It always seems that I do this with my last cutoff wheel. I now buy them in stacks of 50 from amazon.

Answer 5

The bolt looks like a lost cause. I assume you'll be replacing it with a new one?

First try this: Get a good wrench on the nut (closed end preferably). A vice grips set very snugly should work too. Find a way to hold it in place so it doesn't spin with the bolt (the floor or a vice or some helping hands) so you have two hands free. Get a good screwdriver (or better yet just a flathead driver head) that fills the slot completely. You might want to run some kind of a metal blade thru the slot to clean it up so that the driver fits in the slot snugly. Get a hex driver with some leverage or another vice grip and grab the shaft of the driver. Twist with both hands until something happens (most likely the bolt will shear off)

If that fails: cut off the bolt flush with the nut. Get a drill bit the size as the bolt and drill out the bolt inside the nut. Go as far as you feel comfortable (no need to go completely through the nut) and re-try the above technique.

Answer 6

Use a mini-hack and get rid of that bolt, along with those washers. The parts on that tank are all wrong. The bolts should be brass and the washers should be rubber, not hard plastic.