mamod rant

A very popular starting point for Live Steam. With their low cost comes a number of problems which can be discussed here
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Roberts wood light railwa
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mamod rant

Post by Roberts wood light railwa » Mon Apr 20, 2015 6:30 pm

problem 1- fitted a uprated safety valve and water top up valve to my mamod, lit it and set it off as normal but then noticed that the gauge glass was bulging badly. as i put the fire out the gauge glass blew and covered me in hot water. i then allowed the loco to cool and replaced the gauge glass and put the old lower pressure safety valve on. when steam tested it i noticed as it began to blow off it bulged again. what am i doing wrong? this is the 4th gauge glass since christmas

problem 2- loose wheel on the axle.

problem 3- my new mamod saddle tank can hardly get its self around my line let alone pull anything.


possible solution to problems.. sell mamods LOL
If its not made to run on rails I'm not bothered

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Post by mikewakefielduk@btinterne » Mon Apr 20, 2015 8:36 pm

Who is the manufacturer? Is it MSS or mamod.co.uk ?

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Post by Roberts wood light railwa » Tue Apr 21, 2015 3:59 am

Old vintage mamod but speaking to a friend I've realised that 40psi was probably a bit high for the gauge glass to take. I also didn't realise that the safety valves I bought are adjustable.

After having disgust the issue with my mate I went outside with the new mss and had a play with the safety valve and got a really good performance from the loco so I'll be trying to get the gauge glass fixed on my old loco bow so I can adjust the safety valve on that too. I just can't seem to get it to seal.
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Post by Keith S » Tue Apr 21, 2015 7:36 am

I recall reading that the gauge "glass" is actually plastic. I wonder if there is an upgrade to this, as of course higher pressure means higher temperature, too.

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Post by Chris Cairns » Tue Apr 21, 2015 7:45 am

The Mamod SL boiler was designed under the Toy Regulations thus it had a working pressure of less than 1 Bar (14.7 PSI), usually around 0.7 Bar (10 PSI). A hydraulic test was conducted on the boiler where the sight glass developed a leak at 120 PSI, sealing again when the pressure reduced to 60 PSI. Thus it would appear that the boiler is quite safe to use at 25 PSI, and possibly up to 40 PSI.

IP Eng adjustable safety valves came set for 20 - 25 PSI, as do Dream Steam ones (unless you ask for a different setting). Not sure what RWM set their adjustable safety valves to. I'm talking about the 1/4" x 26 BSF threaded safety valves here.

The problem with an adjustable safety valve is you need a working pressure gauge to know what it is set to - http://gardenrails.myfreeforum.org/about8661.html

Over the years the sight glass seal has changed from an oval seal to those thin 'O' rings which can be effectively useless, particularly if the boiler backhead has been punched out a bit deeper. Some owners get away with using some sealant on those 'O' rings, but my solution is either a thicker cross section 'O' ring or the oval seals as used by the current Mamod on their rectangular sight glasses (these may need trimming to fit the boiler backhead cut-out). You can also use the current thicker rectangular Mamod sight glass plastic, but again it will need trimming in order to fit into the boiler backhead cut-out.

If you are using a meths burner make sure that the flames are not creeping into the cab - that will easily melt the sight glass plastic. The deflector plate(s) fitted to most 3 wick meths burners do not fully go up to the boiler bottom thus there can be a gap for the flames to creep back (particularly if you have a steam leak from the back of the reverser/regulator valve).

Your saddle tank should improve as it is run in with more running time. These are definitely not strong performers 'straight out the box' as they are only briefly tested on compressed air prior to shipping.

Loose wheels is harder to fix, and they affect the quartering which affects the performance. Some owners have got away with just re-punching the axle ends (never had any real success using that method, and the axles are made of quite soft steel, thus easily bent). I remove the offending wheel by gripping the axle using a pair of mole grips (which will end up putting burrs of the axle which may need filing down, particularly if you are doing both wheels) and gently pulling the wheel off vertically, roughen up the shouldered axle end then refit the wheel using some activator & Loctite 603. Make sure the brass bearing is not next to the wheel or it will be locked in place by the Loctite, and once the Loctite is set make sure to remove all the excess, particularly on the back of the wheel, otherwise it can lock up that bearing again. I set the quartering by eye and make use of clamps whilst waiting for the Loctite to set (I leave it for 24 hours).

Chris Cairns

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Post by Roberts wood light railwa » Tue Apr 21, 2015 4:46 pm

cheers chris thats a great help
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Post by Chris Cairns » Wed Apr 22, 2015 12:31 pm

Unfortunately the thicker cross section 'O' ring that I found works with the standard sight glass plastic came in a box of 165 'O' rings which does not mention their size or code.

It would appear to be 17.3 mm inner diameter & 2.4 mm cross section.

The problem now is finding a trader who stocks this or a very similar size but does not have a minimum order policy (one trader I've found online would require you to order a minimum of 34 'O' rings).

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Post by Big Jim » Wed Apr 22, 2015 6:43 pm

While buying a box of 165 to get one might be a bit OTT. I find it is very useful to keep an assorted box around. You never know when you might need one!
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Post by DLRdan » Wed Apr 22, 2015 8:01 pm

Just to check, you are using the proper replacement sight glass and not a home made one from Perspex ?

The loose wheel can be cured by using a pair if Philips head screwdrivers. Re quarter the wheels by eye, then place one screw driver in a vice so that it cant move, the offending axle over the head of the screw driver, then the other screw driver on top. Give the top screw driver a sharp tap with a hammer and it should lock the wheel back on the axle. Ive done it a few times now and seems to work though an extra pair of hands is helpful.
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Post by Roberts wood light railwa » Wed Apr 22, 2015 8:03 pm

DLRdan:110344 wrote:Just to check, you are using the proper replacement sight glass and not a home made one from Perspex ?

The loose wheel can be cured by using a pair if Philips head screwdrivers. Re quarter the wheels by eye, then place one screw driver in a vice so that it cant move, the offending axle over the head of the screw driver, then the other screw driver on top. Give the top screw driver a sharp tap with a hammer and it should lock the wheel back on the axle. Ive done it a few times now and seems to work though an extra pair of hands is helpful.
Yes I'm using a replacement from manor models.

Ah brilliant I'll give that a try

Thanks alot
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Post by Boustrophedon » Wed Jun 17, 2015 9:01 pm

I have recently been given 5 mamod stationary engines to repair, all have melted/failed sight glasses. Is there anyone who stocks sight glasses in proper glass, preferably pyrex?

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Post by Roberts wood light railwa » Sat Jun 27, 2015 9:20 pm

not that i know of
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Post by Boustrophedon » Mon Jul 27, 2015 9:13 pm

The sight glasses on Mamod loco's and stationary engines is made of perspex, or PMMA. This softens noticeably at 120C. Any rise in steam pressure also requires a rise in temperature. Perspex really is not suitable for anything over the one bar setting of the original safety valve.

Where are my steam tables? Last used them in 1980.

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Post by H2o » Sun Jan 29, 2017 10:15 pm

Like a total idiot , I boiled one of my Mamods dry, I was very pleased to have the plastic sight glass,

I replaced the mess when cool and lit her up again , no issue, glass is not going to give you that protection. This was a very rare mistake and I do not normally leave an engine or neglect it.

My take on the sight glass

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Post by Boustrophedon » Mon Jan 30, 2017 7:42 pm

What did it protect?

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