Mamod Ceramic Gas Burner

[Chris Cairns]

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]

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]

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]

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

[Chris Cairns]

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]

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]

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

[DolwyddelanLightRail]

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]

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]

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

[Chris Cairns]

We have previously discussed these speed bursts before.

One theory I had read on-line was it is due to water in the boiler boiling over and going down the steam pipe.

Lloyd (steamie1) had done some trials with his Mark II and decided that the speed bursts were least when he used Roundhouse 220 steam oil.

The Mark I has a shorter run steam pipe to the cylinders (no cab lubricator, although I've fitted a dead leg one at the front) than the Mark II/Saddle Tank yet I get more speed bursts with this loco. Now is that because I have not modified the Mark II/Saddle Tank burner venturi's yet?

And the old Mamod SL/MSS & IP Jane locos were not affected by speed bursts?

I also thought it might be a function of the reheat tubes that Mamod fit to their boilers, although the William boiler has none (and since I modified the burner it has had no more speed bursts).

Another Mamod mystery!

John, an interesting discovery with your burner. I previously did some trials (Page 1 of this Discussion) with my Cheddar & Bix jets into the Mamod burner but did not get all of the ceramic to glow red. I also found that the Mamod jet holder had a much shorter thread cut into it so I could not screw a replacement jet all the way into the holder. We have also determined that Mamod are using a No.5 jet so your 'Mersey Tunnel orifice' sounds like a one off (as I recall your Mark I was actually an early Mamod Train that was supplied to Garden Rail for review).

Mike, sadly Brandbright do not list the specifications of their light & thick steam oil. Given that they are supplied by 'one of Great Britain's major oil companies' I suspect one will be ISO460, which is what Mamod & others are using.

Chris Cairns.

[Aizoon]

Indeed, Chris, the jet doesn't screw all the way into the holder, but PTFE tape covers a multitude of sins The result is perfect, though. Nice cones of blue flame and glowing orange-red ceramic. Gives me all the steam I could ever need.

As you say, it was a review loco, so the jet might have been changed since. It's now a better burn than the Mark II as supplied, though.

[mikewakefielduk@btinterne]

Chris: sadly Brandbright do not list the specifications of their light & thick steam oil. Given that they are supplied by 'one of Great Britain's major oil companies' I suspect one will be ISO460, which is what Mamod & others are using.

Ordered some ISO220 from Roundhouse instead. They were pretty concerned I didn't actually own a Roundhouse loco to use it on and were worried I might damage something as "other makes of locos are designed to run on thicker steam oils".

So now I'll have thin oil, a smallish quantity of Mamod ISO460 (which is what I normally use in my locos) and some really thick ISO680 which I bought to try and stop the Mk11 getting through oil so quickly. Intend to try them all to see if different viscosity makes any difference to the Mk11 speed bursts and whether I get the same results as steamie1. Maybe this Friday if I'm not found other things to do........

Speaking of burners, whatever the faults of the Mamod ceramic burner, at least its quiet. My Ragleth and my newly acquired S/H Konrad are both really noisy, especially the Ragleth which sounds like a 747. Both have gas poker design burners - just a brass tube with holes in the top and the far end pinched closed. I moaned to Accucraft and they sent me a British Made gas jet and a wider ring to adjust the air mix, but its not much quieter. With my Mk11 I can hear it start to chuff really impressively when it tackles the uphill gradient on my outdoor track whereas with the Ragleth it just sounds like Heathrow.

Aizoon: 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.

Interesting. So when Peter Johnson told me he'd put a No.20 size burner in the Thomas Telford as part of his efforts to get it to steam properly, it wasn't the first time Mamod had been experimenting with large gas jets.

Mike

[dougrail]

Hmm. Just as a point to Chris regarding his trials, does anyone know what thickness/grade Accucraft's 'official' steam oil is? I use it now in my RWM-Janet and it seems to work fine but wonder if RH oil would be better ?

[Chris Cairns]

What oils should I use with my live steam loco?

To lubricate the valve gear, axles and crank pins use a light machine oil, e.g. 3 in 1 oil. We recommend 460 steam oil for the locomotive lubricator. Accucraft now supply their own brand, available from our dealers.

[Aizoon]

FWIW I use Roundhouse ISO 220 oil on my drip lubricators for the cylinders on my New Mamods and 3-in-1 on the motion and axles.

Slightly worried yesterday when the Sage was having problems with its 2 Kg load on the test track. Then I discovered the the end of the starboard cylinder had come unscrewed!

It was valiantly trying to haul my maximum test load on one cylinder with the other leaking like a Government department. Solid beast, that Mamod Train.

[mikewakefielduk@btinterne]

OK, I managed to test different oils in my Mk11, in particular looking for signs of sudden short speed bursts. I tested each oil in turn using a warm Mk11 and emptied the inline lubricator every time between runs, using a syringe with a curved needle. The MK11 burner has been drilled out to remove the venturi.

I started with ISO 220 from Roundhouse, then ISO 460 from Mamod and lastly ISO 680 from a steam fair somewhere. I then reversed the process, starting with ISO 680 and working down to ISO 220. Each run lasted 4 minutes.

On both occasions, using the ISO 220 I didn't observe any speed bursts but this oil was the most runny, covering the front plate of the loco and causing the burner to flair up and smoke as surplus oil ran onto the front of it.

Using ISO 460 I experienced 2 - 3 speed bursts, the oil was less runny although the odd bit did get onto the burner.

Using ISO 680 there was one slight speed burst on the first run and none on the second. No oil got onto the burner but the the loco did seem to run slightly slower either because not so much oil was mixing with the steam or the oil was simply thicker so causing slightly more resistance.

My conclusions are that, as the only loco to experience speed bursts is my Mk11, there is something in its design that causes speed bursts with two of the three oils. At first I thought it must be something to do with the oil/steam mix in the superheater tube that runs under the boiler above the burner but my Ragleth has the same sort of arrangement and it runs smoothly using Mamod ISO 460 oil. So I really have no idea.

Now the question of what oil to use for real. The answer is I don't know. The ISO 220 would be my choice except for the mess on the front of the loco plus oil getting on the burner makes me think the odd speed burst might be the lesser of the two evils as I have read somewhere that getting oil on a ceramic burner damages the ceramic.

Mike

[Chris Cairns]

Mike,

Thank You for taking the time to conduct and then report on your oil trials.

I'm still unsure what is really causing these speed bursts. I experienced them on my William & William II locos but since drilling out their burner venturi's they have had no more speed bursts. Their lubricators are at the front of the loco after the steam pipe runs through the burner flame.

My Mark I had several speed bursts even after drilling out it's burner venturi and again it's lubricator is fitted at the front of the loco after the steam pipe runs through the burner flame.

On the Mark II & Saddle Tank locos their lubricators are in the cab from where the steam exit pipe then goes through the burner flame.

It appears to be a factor of how hot the steam is in the steam pipe and that is influenced by whether it contains oil, the routing of the steam pipe (in the William family it is mainly through the combustion chamber - in the others it runs through the cab first), and possibly the type of copper tubing used (wall thickness).

Chris Cairns.