Sunday, 27 March 2016

You have to be a bit eccentric...

During the week commencing 21/03 there was quite a bit of activity on CR828. Work continued on the boiler to get it ready for the hydraulic test requested by the Boiler Inspector. All we need now is the pair of large blanks required to blank off the safety valve mountings and we'll be good to go.

The crankaxle has had a lot of attention. Colin Boyd measured up the crankpins for ovality and parallelism. We knew from the previous overhaul that the RH pin is slightly tapered (for reasons unknown) and Colin confirmed that this is still the case. Now that we have the sizes Nathan will be able to machine the big end bearings to size and then we can get them scraped in to the required fit.

For the first time in more than half a century the eccentric sheaves have been removed from the crank axle. This is not a job for the fainthearted but Alan French made up an excellent special tool that allows the square headed clamping screws to be accessed deep inside the eccentric castings. The castings are a beautiful piece of 19th Century workmanship but they are heavy....very heavy..! Once the sheaves were removed it was a matter of cleaning them up and then reassembling them so they can be checked for wear. Three out of the four were found to be surprisingly unworn but the RH forward eccentric is the exception and shows about 0.037" of ovality. So that we give the newly white-metalled eccentric straps the best start in life all of the eccentric sheaves will be mounted on a mandrel in the big lathe and skimmed back to full circularity. There is therefore a lot of lathe work coming up in the next couple of weeks...

Removing the gauge glasses in preparation for the boiler hydraulic test. The regulator handle will need a lot of polishing before 828 goes back into service.....

View looking into the smokebox during replacement of the five washout plugs. JF MacIntosh designed the Dunalastair boiler to generate large volumes of steam (828 has a Dunalastair I boiler and Dunalastair II cylinders and motion) and the number of boiler tubes testifies to this...not much room for water...!

A grubby hand inserts the rearmost fusible plug into the roof of the firebox.....the firebox has two fusible plugs, the purpose of which is to alert the footplate crew to very low water level in the boiler. The plugs are hollow and lined with lead. At normal water levels the lead is kept relatively cool. If the water level gets too low the lead quickly overheats, melts and is blown out of the body of the plug. This is followed by a jet of steam and water blowing out into the firebox. This immediately alerts the crew who should take appropriate action to try and increase the water level as quickly as possible. At the subsequent official enquiry the Driver and Fireman will have a lot of explaining to do.....!!!

Removing the gauge glass fittings requires some special tools......!

Bothe gauge glasses removed and blank flanges fitted for the hydraulic test
Concentrating hard - Colin Boyd is using a large micrometer to record very accurate measurements on the RH Crankpin. JF MacIntosh sized the bearing surfaces very generously on his locomotives. The crankpins on 828 are 8 inches in diameter. It was features like this that made the MacIntosh locomotives perform so satisfactorily and achieve such long lives.

The Caledonian Railway in MacIntosh's days preferred to build their locos with inside cylinders. This gave greater stability and reduced wear and tear on the track (outside cylinder locos have a tendency to sway from side to side under the power impulses from the pistons). The price for this was the requirement for a very complex crank axle. The Caley used a variety of types of crank axle but by 1899 when 828 was built they used fully built up steel axles. Because these were very costly and time consuming to manufacture they were bought-in from outside contractors. Here, on one of 828's RH crankwebs we see the identification number that allowed the Caley (or LMS) to trace the manufacturing records of this particular axle. Note also the highly polished surface of the journal for the axlebox bearing.

Crank axle with the RH Eccentric Sheaves removed. The LH Eccentrics are still in place. The leftmost of the two is the eccentric that gives forward motion; the other one gives backward motion. 

The crankaxle with both sets of eccentric sheaves removed. As a "fully built" axle it consists of nine individual parts pressed and dowelled together. Manufacturing a replacement would be horrifyingly expensive today....!

One half of the LH eccentric sheaves being cleaned in the Shed's parts cleaner - a very useful piece of equipment indeed.
Both sets of eccentric sheaves on the bench at the north end of the shed. It takes three people to lift them when they are assembled. Nathan Lightowler is measuring the diameter at 90 degree intervals so that we can check for wear.

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