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john brown 1711/10/2021 07:53:07
135 forum posts
3 photos

Hi all was given a mamod steam engine to se if l could repair it as the boiler has had a big dent in it ,now am happy to replace the boiler tube ,but the only thing is all l have is of the right size is thick walled seamless brass tube,will that be ok to use ,what is the experts opinion please.

Thor 🇳🇴11/10/2021 08:20:15
1437 forum posts
41 photos

Hi John,

Using brass for the boiler may lead to de-zincification of the brass so it looses its strength. Use copper tube instead.


Roger Best11/10/2021 08:35:04
318 forum posts
36 photos

Do you want to run the engine or just admire it on the shelf John?

From a performance point of view I think that it will be OK, copper is a good conductor and although there will be more to warm up it will still heat up the water.

The practical issues are that you will need to make new ends, so its not an insignificant amount of work. On the other hand it is an opportunity to make improvements, like raising the operating pressure, or fitting hedgehog pins or pipes to raise more steam. If you go that way I suggest you use gas to fire it.

However most dents can be removed from a toy boiler, lots of annealing and careful beating can do a great job and filling it with water and putting it in a freezer can stretch out badly crumpled boilers, so please post some pictures and we can assess what is needed.

There are plenty of stories about dents on the Unofficial Mamod Forum

Here is a typical example: Dented MM1

john brown 1711/10/2021 08:44:52
135 forum posts
3 photos

Well have just had a look at it and it seems that the boiler was made in brass in the first place,would think the meths fuel would run out before the boiler ran out of water,and would think that it will not have a lot of use,but will se if what more posts will bring ,as for repairing the dents ,no go its bad ,can get dents out of most things but not this time.

John Olsen11/10/2021 09:20:54
1216 forum posts
92 photos
1 articles

Mamod boilers are brass and dezincification does not seem to be a problem.

How bad is the dent? Is it worth worrying about? They run at a pretty low pressure, and provided they are used with the standard burner are pretty much inherently safe, eg if the safety valve was blocked off the burner would be unable to build up enough pressure to burst the boiler. Also the burner would be unable to heat the boiler up to a temperature that would soften the joints or damage the material even if bone dry. They are below the size where there is any legal requirements in most countries.


Ady111/10/2021 09:37:00
4827 forum posts
724 photos
Posted by John Olsen on 11/10/2021 09:20:54:

Mamod boilers are brass and dezincification does not seem to be a problem.

Now that's interesting, some of those models are decades old

Mike Hurley11/10/2021 09:49:12
210 forum posts
70 photos

Just out of interest, I live a stones throw from one of what used to be their factory back in the 70's (its now a health club - closed). Employees used to be able to buy models that were ' for display only ' at a nominal cost - these had failed the rigorous quality control and just had a hole drilled through the boiler at the bottom, you couldn't see it so they did make a nice shelf mode l- I've still got one sitting in my workshop - the traction engine

Yes. the boiler is brass.

regards Mike

Grindstone Cowboy11/10/2021 10:00:57
761 forum posts
60 photos

I'm with John Olsen on this one. None of my Mamod boilers show any sign of de-zincification after years of use - but always with the supplied meths burners.

As some may remember from school science lessons, you can heat a paper bag of water with a candle flame with no damge to the bag, as long as the water is in contact with the inside of the bag wherever the flame is in contact with the outside. The heat is conducted away quickly enough to prevent burning the paper.

I'd say the same principle holds true for the Mamod brass boilers. All bets are off if you either run out of water, or use a heat source that supplies heat faster than it can be conducted away.


Thor 🇳🇴11/10/2021 11:54:25
1437 forum posts
41 photos

Some brass alloys do resist dezincification, what alloy John's brass tube is I don't know, so if making a new boiler that will be fired, copper would be safer unless you know what brass alloy is used in the brass tube.


Roger Best16/10/2021 14:37:55
318 forum posts
36 photos

Its not entirely true to say that Mamods don't get dezinc, compromised boilers turn up on occasion, usually the stationary engines, however compared to the numbers produced and the age of the toys concerned its a low proportion so Mamod's suppliers should be proud.

Some other manufacturers have a dreadful reputation.

noel shelley16/10/2021 15:31:44
870 forum posts
19 photos

Brass can age and crack, so pushing the dent out even after annealing, which may cause the soldered joints to part could be risky - proceed with caution. What Dia is the tube ? Noel.

kevin laxon16/10/2021 16:20:06
10 forum posts

I had the job of repairing a Mamod roller boiler years ago where the solder had failed & let the inserts turn,the entire boiler appeared to be brass as did the insert's,all joints were soft soldered, one think that struck me was the entire internal surface of the boiler was tinned,I can only assume to stop the Brass coming into contact with water & hence prevent dezincification,could this be the case??.

JasonB16/10/2021 16:27:39
21649 forum posts
2495 photos
1 articles
john brown 1716/10/2021 16:53:53
135 forum posts
3 photos

Thanks jason am clear now with what to do ,so will make a new brass boiler,and if it was made when new with soft solder then l will use that as well,but will test it to its double working pressure.

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