Tuesday, 19 January 2016

Here are a few views of the motion parts being removed from 828 in preparation for lifting her off of her wheels. It's worth pointing out the disadvantages of working on an inside cylinder loco. While the people working on 828 were struggling with heavy parts in the confined space between the frames other SRC staff members were cheerfully removing similar parts from the outside of 46512 EV Cooper Engineer...When the Caledonian Railway Company built 828 in 1899 the science of metallurgy was developing rapidly - even as late as the 1880s it was normal practice to make use of iron rather than steel. But by 1899 steel manufacturing techniques were being refined and expanded at a rapid pace and thus 828 makes extensive use of the low-alloy steels that were becoming widely available in 19th Century heavy engineering. From our perspective in the 21st Century "heavy" is the appropriate word. 828's connecting rods are steel forgings and they weigh just under 400kg each, which makes their removal something that needs to be undertaken with caution..but rather than depress ourselves right now with the connecting rods, lets look at the removal of the somewhat lighter valve eccentric rods and spindles...

The view from beneath....! Imagine you're standing in a three foot deep pit in Aviemore Shed underneath 828 and looking backwards towards the driving (middle) axle. This is what you see...! From right to left we see the LH Driving Wheel, the axle box suspension springs and above them, bolted to the frame, the fractured LH Driving Hornblock. Next is the LH Connecting Rod with one of its two large bolts visible at the bottom. Then we have have the four eccentrics and their eccentric rods that form the basis of the Stephensons Link valve gear that drives the slide valves to allow admission and exhaust of the working steam. Finally, on the left is the RH Connecting Rod. If you are impressed at how clean it is you can thank Dave Green who spent a day under the loco with a steam cleaner removing the oil and grease that normally saturates the motion and the inside of the frame plates...!

Look! The first of the four eccentric rods has been disconnected from the expansion link that it normally helps to swing. This one is known as the RH (right hand) Back Going Rod. It is attached to the bottom of the RH expansion link and its purpose is to give the principal valve movement to the RH Cylinder when the loco is running backwards. By a very clever piece of geometry it also helps to modify the valve events when the loco is running forwards.

Now we're crouching on the RH running plate and looking in at the valve spindle extension rods which can be seen emerging from their large support bushes mounted on the Motion Plate. The odd looking linkage on the LH Rod is the patent drive to the Mechanical Lubricator that ensures positive lubrication of slide valves and other parts of the valve gear. At the far left hand side are the LH Slide Bars and in the middle you can just see a vertical bolted joint that is the joint between the two halves of the cylinder block casting.

This picture shows the connection between the valve spindle extension rods and the valve spindles. The valve spindles are pulled up into a tapered socket and held firmly in position by a tapered wedge. The RH tapered wedge has been temporarily refitted after the spindle has been separated and pushed forwards.

Out in the open, just behind the front bufferbeam and below the smokebox door the "piano lid" has been removed and we can see the front covers of the two cylinders with the steamchest cover in between them. The steamchest cover has to come off to allow removal of the valve spindles. On the far side of the picture can be seen the extensive remedial work that was carried out in 2014 to strengthen the connection between the front bufferbeam and the main frames. 

The steamchest cover has been removed and we can see the two valve spindles. The slide valves themselves are the two bronze inserts in the valve yokes. 

Close up of the end of the valve spindles

Slide valve removed from its yoke (the yoke is lying on the shed floor). The valves are made from a phosphor bronze alloy. Because 828's cylinder block is quite old, the port faces that the valves move back and forward over are worn to an odd shape. It takes quite a while for new valves to bed in and form a good steam-tight seal. You can see the ridge that needs to form where the finger is pointing. When the next heavy overhaul is carried out it is quite probable that the cylinder block casting will need to be renewed.....

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