The following article was written by MamodMan, a founding member and moderator of the Unofficial mamod and other steam Forum. I thought it was such an excellent article that it would be a good idea to republish it here, with permission. I have made no amendments, this is a verbatim reproduction - I have just removed references to threads on the newsgroup.

This article has caused some controversy, with a few people questioning the safety of the operation. Personally, I think it's perfectly safe to work on a boiler, as long as you're sure you know what you're doing. If at all unsure: leave it to the experts. But just in case, I will accept no responsibility for any mishaps - the information below is strictly face value.

I'm going to try and make this cover as many parts as possible that hopefully means, threads, pipes, boilers and obviously the clean up. I have used these steps pretty much most of my soldering life and never had anything go wrong as yet. Firstly. I'd just like to say knocking the end off a boiler is ESSENTIAL to solder some and most things. It won't ruin your model, that is very naive, it's never ruined mine and i'll show you a few example which have been soldered by myself.

Tools needed:

Small Blowtorch, plumbers blowtorch or similar. Can be bought on ebay or in D.I.Y stores. a soldering iron won't do it!

Some thin plumbers solder, preferably lead based as it has a lower melting point and is easier to work with.

Some Flux, very important to use this around the threads to make the solder flow better.

Many grades of wet and dry paper, wire/steel wool etc for cleaning purposes.

A vice/work bench is needed too

Resoldering a thread

Ok, firstly i'm going to tell you how to solder a thread from the inside. Personally from a collectors P.O.V I hate boilers with solder slapped over it everywhere, looks messy, is messy and could potentially go at any minute. Firstly you need to strip down your engine as far as it will go, right down to the boiler. If this is an SE3 then that's easily done, likewise with most earlier SE engines.

1) Secure your boiler into the vice. You could use a soft cloth either side so you don't ruin the brass work. Then take your blow torch and gently start to heat around one of the ends. It's important you find out which end come off first. Most early engines 60 and below both ends may come off. If it's 70's+ then with Minors it's usually the front end. Most other startionarys the back end. As you are heating take a small flat ended tool and gently knock around the lip on the cap. Keep the blow torch in place while doing this and eventually the cap will start to lift off and eventually fall off. Again a good idea to make sure it doesn't land on anything hard.

Once the end is off you MUST wait for it to cool down otherwise your skin will no longer exist on your hands. A damp cloth can help
icon_smile . Simply cool it down and take it out the vice. You will end up with this baby:


As you can see it's all limescaled. Ok, now, choose the thread that needs soldering (which ever is loose in the boiler). Take the thread out if it already isn't then move tio step two:

2) You now need to take some wet and dry paper and sand as much limescale away as possible. You basically want it to go back to the brass. I find its best to do it only in the smallest area around the thread otherwise the solder seems to wonder where it likes
icon_biggrin . Once you are back to the brass inside the boiler where the thread needs to be soldered then take this next step. You need to clean up the thread which needs to be soldered as much as possible. If you can sand with wet and dry then that's fine. Obviosuly, only remove the limescale and not too much of the thread Once both parts are clean you are ready to move on to the next stage.

3) Secure the boiler upside down in the vice. Meaning, all the threads along the top of the boiler are now closest to the ground. You will need some flux around the area you wish to solder on. Helps to get quite a bit around so the solder runs properly. Pop the thread back in and get some flux around that too. Gently, heat the whole area up until the flux melts. now you need to wait until the solder will melt so keep heating. Then take your solder and literally run it around the thread. I use semi-circular motions all around the thread so I can get to the back and both sides. The solder will run around the thread and when you are satified it has soldered up you then turn the heat off and leave to cool down a bit.

Sometimes, rarely you may get some come through the top, but all you need to do is keep the heat down to minimum, heat around the top and wipe the solder off carefully with wire wool. If it leaves a silver streak don't worry, we shall remove later
icon_biggrin .

4) Once you are satisfied the thread is steam tight, good to test. Just puddle some water around the thread and see if it stays in there. If it does then chances are she's steam tight!.. Nexy, you need to wet and dry around the boiler edge. This means the outside of it where the engine was previosuly soldered. Just make sure it's level. Then get some flux around it and push the end cap back on your boiler. There are now two schools of thoughts. You can heat it up and hope the old stuff holds it but i prefur this way:

5) stand the boiler in a work bench/vice, so the cap you wish to solder is facing/closest to the floor. So basically it looks like a smarties tube when standing on a table. Then take some thin solder, start heating around the lip where the end cap is on the boiler and gently run your solder all the way around the lip. You got some flux on so it should run right round. That will now be a safe and steam tight boiler ladies and gentlemen.

The clean up

If any solder has come through at some point we will need to clean it off. Simply as before you need to remove all blobs of solder and get the boiler silver as it were. It's quite rare to get some over spill on the boiler but you never know.

1) Take some very fine wet and dry 800 grade and gently working one way, take the solder off the boiler. It will leave it scratched for the time being. Once all solder is removed then simply polish it 2-4 times and the scratches will dissapear, usually after the first Brasso anyway
icon_biggrin . Then you are done! put the engine back together, fire it up and enjoy! icon_biggrin . A few example in my collection that have had this treatment.


No solder, how would you know the end cap has been off? you can't! because it's clean and steam tight!


All threads were resoldered on this engine! Union nut, Safety valve, over flow and whistle.

This one has been soldered more times than anything! now? clean as a whistle


The majority of that was soldered. Don't forget someone else sanded the boiler with W&D all over, now it's a wonderfully clean and good working model.

There is nothing to fear, just follow the steps and you will be fine guys. You won't even know it's been done, and if anything, it will keep the thread in place for much longer.