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While the main focus of the Strathspey Railway is running steam trains for the paying public, a small but dedicated group of volunteers has been restoring other items of heritage interest in spare moments between working on the loco fleet and improving locoshed infrastructure and facilities.

The current project is a Ruston Hornsby 48DS diesel shunter of 1948 which worked at Longmorn distillery until 1980 (even though Dr Beeching had closed the adjacent main line in 1967). Because it was presented to the Strathspey Railway repainted with advertisements for Queen Anne blended scotch whisky, it is known to most people as “Queen Anne”.

To find out more about our aims, follow this link or click the [About] button above.

This Blog was started over 5 years after the project began, so most of the initial blog entries are retrospective.

Thursday, 25 January 2018

Radiator Grille & Compression Testing

Until recently, there has not been enough spare time to make much progress on Queen Anne, but we now have something to report.

Radiator Grille

The original radiator grille was made of mild steel mesh with a mild steel strip around the edge.  Not surprisingly, the bottom part of the grille was a rust trap and was badly corroded along with lower part of the bonnet that it was bolted to.  So it was decided to replace it with stainless steel this time.

The old grille used ¼ inch 16 gauge woven mesh.  The nearest stainless steel equivalent that can be obtained in small quantities is ¼ inch 18 gauge.  We hope no-one will notice the difference.  Suitable stainless steel U-section strips were also obtained to act as a “hem” for the edges of the mesh.  The grille had been fixed on by 5/16 inch Whitworth dome-head bolts, so suitable replacements were turned up in stainless steel.

The mesh was cut to size and the U-section strips were mitred and fitted round the edges.  The mitred corners were then TIG welded together.  The mesh was positioned over the aperture in the bonnet and the U-sections drilled to match the mounting holes.  The resulting grille is better than new.
Radiator mesh and edging strips

The bonnet with its new grille

Compression Testing

When running the engine, it was noticed that cylinder No. 1 did not appear to be firing, and simply generated clouds of unburnt diesel.  The rings and cylinder liners are new, and we had previously pressure-tested the cylinders.  The test showed that there was very little leakage past the valves or pistons on any of the cylinders.  The spray patterns of the injectors seemed OK, so it was decided to do a compression test.

A simple automotive compression tester kit was bought.  This came with lots of adaptors for modern engines, but none for a Ruston 4VRH, so an adaptor was made to fit the Ruston engine.  The non-return valve was fitted at the bottom end of the adaptor to provide the best reading.  The tester with the Ruston adaptor is shown below.
Compression Tester and Adaptor

The compression tester was fitted to each cylinder in turn and the engine cranked round.  Pressure readings were as follows :-
  1.    290 
  2.    330
  3.    320
  4.    310
The test clearly showed that cylinder No. 1 had significantly lower compression.  It was probably no coincidence that this cylinder had the slightly bent con rod, so it was decided to remove the cylinder heads No. 1 and No. 2 and take some measurements.

The cylinder heads are essentially flat and the piston has a large recess in the crown to form the combustion chamber.  The top of the piston crown at its highest point should ideally be level with the block.  By using a dial gauge, it was found that No. 1 was 40 thou below block level, suggesting that the con rod was short.  This was almost certainly due to the fact that No. 1 and No. 2 cylinders were seized due to water ingress through the exhaust after the loco had been abandoned.

Subsequently a measurement was made of the volume of the recess in the piston crown by filling it with water.  Knowing that the cylinder capacity is 4 ½ inches diameter by 5 ½ inches stroke, the compression ratio comes out at 13.5 to 1.  This is very low for a diesel (modern ones are usually at least 16 to 1), but in 1948 they were probably happy to have a low compression ratio because although the efficiency is less, the crankshaft and crankcase do not have to be so strong and heavy.  The extra 40 thou of clearance on No. 1 reduces the compression ratio to about 12.5 to 1, which is borderline for a compression-ignition engine.

Extensive enquiries were made to see if a replacement con rod could be found, but the search drew a blank, so Plan B was put into operation.  This involved making a new little end bush and boring it eccentrically to bring the piston to the correct height.
No. 1 Con Rod with eccentric bush & old bush

The con rod and piston were re-fitted and the height of the piston re-checked and found to be correct (level with the top of the block within a few thou).  The heads have now been replaced and the engine awaits testing.  It will be tested initially without the exhaust manifold so that the exhaust from each cylinder can be compared.
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