Mamod Ceramic Gas Burner

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Sun Mar 17, 2013 1:20 pm

Mamod O rings are made of nitrile which is ideal as it is resistant to petroleum substances as well as a high range of temperatures. Nitrile O rings are usually black although I have seen them in other colours so I don't think the colour is particularly significant.

On the other hand silicon O rings are usually red, but again can be other colours as well. Silicon wouldn't be as suitable for loco cylinders as it can be attacked by some petroleum substances.

Mike

dougrail · Post by **dougrail** » Sun Mar 17, 2013 1:46 pm

I'm using the colour only as a means to identify them. I'm just wondering whether the o-rings in the slide-valves are the right type/too stiff?

Chris Cairns · Post by **Chris Cairns** » Sun Mar 17, 2013 4:27 pm

Unfortunately most types of 'O' rings are available in most of the colours, so colour alone is no way of identifying the type of 'O' ring used.

It is not the Shore Hardness (Doug's flexing, but most are of a standard Hardness) but the type of material used that is important.

Silicone is not suitable for wet steam, all but one source I reviewed on-line say that Nitrile is also not suitable for wet steam, with Viton or EPDM being the choice for wet steam. So if Mamod are indeed using Nitrile then that might be causing the stiffness problem which is being hidden by the 'lack of steam' theory.

Over on Hornby OO Live Steam we are experiencing a similar stiff running locomotive problem (but it does not affect every locomotive, as they are all very individual in their performance), and the Supporters Club are doing a trial with red Viton 'O' rings. Unfortunately I've still not fashioned the oddly sized spanner to remove the piston gland housing so have not joined in on that trial yet.

Chris Cairns.

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Sun Mar 17, 2013 4:41 pm

A good few weeks back, when Mamod first said they were having problems sourcing O rings of exactly 11mm OD (apparently the only ones they could get measured 11.2mm OD) I had a dig through my spares box and came across an unopened packet of rings which measured exactly 11.0mm OD. I offered them to David Terry to try and he said they would be fine so long as they were made of Nitrile, which they were.

From that conversation I presume Mamod O rings are made of Nitrile.

(It turned out that the O rings I sent had an internal diameter of 7mm while Mamod needed 7.5mm, so I don't believe they were ever used).

Mike

spooner · Post by **spooner** » Sun Mar 17, 2013 5:53 pm

One thing with O rings that they have to have another room to roll in thee slot.

Chris Cairns · Post by **Chris Cairns** » Sun Mar 17, 2013 7:30 pm

they have to have another room to roll in thee slot.

Say again!

Chris Cairns.

spooner · Post by **spooner** » Sun Mar 17, 2013 7:49 pm

Slots for O rings are meant to be a certain percentage larger than the O rings.

Aizoon · Post by **Aizoon** » Mon Mar 18, 2013 12:02 pm

Chris pointed me at this thread in Another Place. Thanks, Chris.

I have a Mamod Train Mark II and also had the problem with a blowback caused by leakage between the jet holder and the burner tube, but fixing it in firmly seems to have cured that even without PTFE tape.

The flame is still too yellow, and only the edges of the ceramic glow red, unlike the Bix burner on the Thing which is a solid cheerful red.

I'm wondering about drilling out the venturi to 6 mm. Good idea or what?

I'm getting pretty solid runs now, so maybe it's not necessary...

PS I also have a Mark I, but that's another story.

Chris Cairns · Post by **Chris Cairns** » Mon Mar 18, 2013 5:37 pm

John,

The good thing about the Mark I & II locomotives is they are very good runners mechanically and do not need a lot of steam pressure to run unlike the piston valve locomotives.

My initial response was to answer your condensate blocking the oscillating cylinders problem, which is probably being caused by the steam condensing in the steam pipe as it goes through your weak (yellowish) burner flame. As the Mamod jet holder does not allow much in the way of air adjustment like you have on the Bix burner, the only other alternative I see to improving the burner is to drill out that venturi. So far I'm the only one to do that here as everyone else is happy with the way their Mark IIs run.

It has certainly transformed both my William ( http://gardenrails.myfreeforum.org/about6899.html ) and my William II, but I'm leaving the rest of my Mamods until after I've cleared other workshop projects (trying to get a feel for my shopping list for the Peterborough show).

No photos were taken during my recent venturi drilling (forgot!) but what I do, after getting the burner out of the chassis which is awkward on the Mark I & II with those spacing washers, is place the burner in my mini vice, insert a 4mm drill in reverse (blunt end first) to gauge the depth required until you meet the ceramic material inside the burner, then drill 6mm to just short of that depth. You will get a lot of swarf inside the burner which needs a good shaking/blowing out.

The ceramic material goes to approx the line on this photo -

I do find that this modification means the burner gets hotter now and running around in my kitchen it will suffer from the occasional pop-back to the jet. Carefully reducing the gas valve stops the pop-backs (although I use my extractor fan in the kitchen there is no ready supply of cold air coming in, and I watched the temperature increase by 3 degrees Centigrade whilst running my William II!!).

Hope the above makes sense.

Chris Cairns.

Aizoon · Post by **Aizoon** » Mon Mar 18, 2013 5:55 pm

Thanks, Chris, I had a superb run on my Mark II "DOMESTIC DRAGON" today, so maybe it doesn't need extra fettling.

See https://www.dropbox.com/s/cwwuv3lltkgx6 ... 155438.mpg

Chris Cairns · Post by **Chris Cairns** » Mon Mar 18, 2013 6:44 pm

Yes it is running well John so like the others here why change it.

At some point I will be modifying my Mark I as it still has a nylon gas pipe. So fitting a copper gas pipe, drilling out the venturi and blocking off the combustion chamber wall holes is all on my 'To Do' list.

Chris Cairns.

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Wed Mar 20, 2013 5:06 pm

I've just drill the venturi out and fired the Mk11 up afterwards. A noticeable change to the ceramic, which is now glowing red hot and it got up steam a bit quicker than before. Ran it on the rolling road for the whole tank of gas. Didn't try outside on the track - too bloomin' cold.

No burner pop-back but I never had that before either.

As yet I haven't tried closing up any holes on the combustion chamber wall but if I do I will probably experiment with a large diameter stubby pop rivet in each hole.

Actually drilling out the venturi proved harder than I thought. I used a milling machine, a 6mm cutter and held the burner vertically in a machine vice as I advanced the cutter down about 1mm at a time. Unlike the burner Chris drilled out, in mine the venturi opening extended all the way in so it was touching the ceramic material. Maybe Mamod have changed the design?

Mike

Chris Cairns · Post by **Chris Cairns** » Wed Mar 20, 2013 7:30 pm

On the 2 I've done so far there was something stopping my 4 mm depth gauge going any further, and if it is ceramic material I did not want to drill into it in case it cracked.

My burner pop-backs were probably a combination of having the gas valve turned up a little high for the piston valve locos (the oscillating Mark I, II & Saddle Tank do not need as much steam pressure), and the air getting too hot in my kitchen (should really run with the window open but too cold for that at present).

When I do my Mark I next I will do a before & after timing comparison.

Given how many of these faulty burners were made I've not seen it being discussed elsewhere on-line. Will Mamod tell anyone else?

Chris Cairns.

Lner fan Sam · Post by **Lner fan Sam** » Wed Mar 20, 2013 7:44 pm

Is there a possibility of you doing a how to vid chris on drilling out the hole on the burner?

Chris Cairns · Post by **Chris Cairns** » Thu Mar 21, 2013 1:52 am

Is there a possibility of you doing a how to video

As my mini vice has just decided to strip its thread then the answer is no. One of my long 'To Do' list items is to build a proper work bench.

Not difficult to drill out, although looks like Mamod have introduced 2 venturis as my 4mm drill goes into the burner so far, but my 2 mm drill goes in even further. Very strange!

Chris Cairns.

Chris Cairns · Post by **Chris Cairns** » Sat Mar 23, 2013 10:13 pm

So my comment above about 2 venturis was just caused by the 4mm drilling not being completed to the end of the tube. A quick run through with the 4mm drill fixed that.

There is still something within the burner before the external ceramic material which stops the drill bit going any further.

After some hassle I managed to drill out my Mark I burner to 6mm. Unfortunately as it has thrown a 'sicky' I could not get a decent comparision before & after timings. Certainly it raised steam quicker and the blue cone pattern is now more pronounced with more of the ceramic material glowing red.

This loco has no burner pop-backs (I filed the jet holder so the retaining screw has a flatter face to grip, and it is mounted flush to the burner). However this loco still suffers from regular speed bursts, even after closing the gas valve off. I plan to get some Roundhouse 220 steam oil at Peterborough to see if that changes these speed bursts.

Chris Cairns.

Aizoon · Post by **Aizoon** » Sun Mar 24, 2013 3:01 pm

I was under the impression that speed bursts were cause by water flash-boiling in the "superheater" - might be wrong, though...

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Sun Mar 24, 2013 3:22 pm

That's an interesting thought about the speed bursts, as I also was under the impression that it was down to water flashing over within the superheater...

mikewakefielduk@btinterne · Post by **mikewakefielduk@btinterne** » Sun Mar 24, 2013 5:29 pm

I also think its something to do with the superheater as my current Mk11 has the odd speed burst even when I've just closed the throttle. I'm wondering whether its got something to do with the steam oil. I'm going to try the stuff Brandbright sells to see if it makes any difference.

Mike

Aizoon · Post by **Aizoon** » Sun Mar 24, 2013 5:31 pm

I think I have managed to get the Mamod Train Mark I burner to behave.

When I bodged mine into SAGE OF WOOKEY, I slightly altered the front mounting so that it's simple to remove the boiler. Curious to find out what the burner was doing, I removed said boiler and lit up. The result was interesting - the ceramic didn't heat up at all, and I was presented with a rather inefficient gas poker. This doesn't show quite so much with the boiler in place, because the boiler itself deflects the flame on to the edge of the ceramic. (Also because you can't get a good look at it in situ).

I removed the gas jet supplied and, taking a good look at it, noted that it has a orifice resembling the Mersey Tunnel, so I replaced it with a Number 6 burner from my things box.

Result! The burner now did its ceramic thing and glowed orange-red, just like the Bix burner on the Thing. With the boiler back in place, it produced all the steam I could possibly need. I am now, officially, a happy bunny

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