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Gauge 1 Steam, BR Standard 4MT Tank Loco 80097.

October 6, 2017

By and large the British Railways standard locomotives, designed under RA Riddles, were successful machines, capable for the work they were intended to perform, reasonably efficient, reliable and easy to maintain. They were also handsome, and I think that the BR 4MT Tank loco is one of the most handsome tank locos of them all. The 4 is the power (the classification for steam is strictly not power but tractive effort and runs from lowest to highest being 9 as in 9F) classification while the MT stands for mixed traffic, i.e. freight as well as passenger trains. I remember as a little boy being taken to meet the crew of one of them at Waterloo station and was strongly impressed. This loco is contemporary with the Rebuilt Merchant Navy Pacific (35028) that I have. I duly located and bought one to partner with said Pacific. Two versions of this model have been released, first by the Gauge 1 Model Company and later by Bowande (Wuhu). The G1 MoCo is now defunct and their designs have to some extent passed on to Accucraft. Both model runs sold out quickly, it is a popular loco! I finally located an elderly one that turned out to need to urgent attention (more below). Given the extent of necessary repairs it needed, I paid too much for it, c’est la vie. The previous owner must have realised what a mess it was in but didn’t come clean with the selling agent I think.

The G1 MoCo model is spirit fired, and is equipped with a draft blower that was completely blocked in my example. It has two cylinders with faux outside Walschearts valve gear (nicely done) and inside valves with slip eccentrics for reversing. It also has an axle and a hand water pump, as is usual with spirit fired gauge 1 loco. (The Bowande version is fired by gas and has no blower or water pump.)


A handsome machine, the A4 too! Maybe the scales below will weigh the relative merits of the designs.

To the troubles: The blower was blocked and this led me to wash out the boiler. Quite a bit of sediment both oily and solid, came out. I washed it out with distilled vinegar three times but was unable to clear the blower line. So, the manifold had to come off. It is held to the backhead by 4 M3x0.5 screws, the upper two screw into blind holes while the lower two are open into the boiler. Well, the top screws came out fine. But, the lower screw heads simply fell off when I applied a screwdriver. I didn’t panic. (Not bad for me.) I pried the manifold off using a wrench on each of the protruding square shaped lugs on each side of the manifold so no danger of scratching the faying surfaces. (The lugs house the blower and regulator valves.) Having done that, I started poking about in the two lower screw holes and thank goodness, the screws had corroded completely away so all I had to do was run a tapping drill and tap through each. With galvanic corrosion between steel and brass or copper, the steel looses. (In fact, it is possible to remove a broken tap in brass or copper by dissolving it using an alum solution and heat. I initially thought I might have to do that.)

I cleaned everything up including the blower line and then re-attached the manifold just using silicone grease (Dow Corning) as the joint compound. I took care to make sure that the threaded holes were well packed with grease. I use this on all the pressure fitting threads too. There is no need to use fibre washers under them. For what’s it’s worth (probably not much) I will replace the screws with stainless steel items when they arrive.


Here’s the cab and side tank covers. I was glad to discover that this assembly is easy to remove, just two screws in the back (just above the buffer beam), two screws into the cab floor from underneath and two screws in tabs at the front of each tank.


I wound up removing the side tanks also. The tank containing the hand pump had been gooped up with RTV and the transfer tube between the tanks was blocked! There was no need for the RTV, the tank doesn’t leak! The joint between the pump base and the tank was the likely culprit. Again, I sealed the surfaces using silicone grease.


This view shows one end of the water balance tube for the two tanks.


The tube has fiddly sprung clips on each end and I have nothing suitable to grip them with so I put a 16 SWG copper wire retainer through the ends and simply snipped it away when the clips were in place.


Running the loco:

Well, I now have fierce blower action.

I repacked the burner tubes with 22 strands of ceramic string, leaving about 3/8″ exposed.

Having filled the lubricator and the boiler, I fitted the fan, opened the spirit tap and lit her up. Pressure rose nicely. I opened the drain cocks and the lubricator valve slightly (too much and the loco will run without opening the regulator). Once around 20lb was showing, I opened the blower and removed the fan. Pressure climbed quickly to an indicated 50PSI. Opening the regulator a little and pushing, plenty of oily water was ejected from the drain cocks. Once that was done, I closed the cocks, opened the regulator again and away she went! She runs with little temperament. The only thing is that the axle pump only just keeps up and that was with no load. Still, with occasional top ups of the tanks she run beautifully for quite some time and kept running until the gauge had fallen to well under half pressure (this includes about 50′ of 1% gradient each lap). The loco clicks as she runs and I have noticed this clicking when watching this design run on YouTube. The axle pump is driven via a bell crank, there are five pin joints between the eccentric and the pump plunger resulting in considerable lost motion, I suspect that with the obvious wear this loco has, the extra lost motion is responsible for the clicking. I also expect lost motion may be responsible for the weak pumping action too. That’s a project for another day because the pump is buried under (or over) the inside valve gear.

Oh, no sign of leaks anywhere! The silicone grease works well.





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  1. Bruce Baur permalink

    As always, a great report Richard.


  2. Bruce Baur permalink

    Thanks, As always, you have great information and reports. Silicone grease is also my friend. It is real helpful in keeping battery terminals from getting eaten up by leaking batteries. Bruce

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