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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.

Friday, 10 March 2017

Spragging Gear


Spragging Gear

Spragging Gear is the name used by Ruston to describe the exhaust valve lifting mechanism that allows the engine to be turned without compression.

The spragging gear helps in starting the engine.  The crankshaft can be rotated much more rapidly (using the starter motor or by hand) if there is no compression.  When the gear is released, the momentum of the flywheel helps to maintain speed while the engine starts.  If the injectors or pump are worn, the initial rotation will prime the injectors and ensure that fuel is being delivered when compression begins.  In favourable conditions, it might be possible to start the engine by hand using this method, although it would require considerable stamina and probably the use of both winding handles (located on either side of the loco).

Each cylinder head has a side cover which carries the spragging gear.  A cam is rotated through 60 degrees and lifts an operating rod by about 80 thou to push against the exhaust valve rocker and open the valve.  The following diagram from the Parts Manual shows the general arrangement.
Spragging Gear Parts for a Ruston 4VRH
Because the gear spends most of its time inactive, it appears to have been under-designed by Ruston & Hornsby.  The cams had become very loose in the covers (there is no effective lubrication for the bearings), and there was a lot of wear in the operating mechanism.  Also the operating levers on each cam had been pinned at inconsistent angles, so the cams were not properly aligned.  The sprigging gear should be set so there is a 25 thou gap when the gear is inactive and the exhaust valve closed.  However because of wear, there was 40 thou of slack, so proper setting was impossible.  In fact, prior to restoration, the gear had been adjusted to a large gap, effectively putting it out of use.

The bearings in the covers were bored out, fitted with bronze bushes and reamed to size.  The bushes have a groove to take an O-ring seal and an oil hole to allow engine oil to drip through.  New cams were made as the old ones had worn bearing surfaces and worn cam profiles.
Cover with new bush.  New cam on left, old one on right
The operating levers for cylinders nos. 2 and 3 have a slot in the end to allow for slight differences in height.  However, these slots had become worn, so it was decided to make new ones to remove the slack in the operating mechanism.  The long lever on cylinder no. 1 had a crude stop on it to define the two positions (30 degrees either side of vertical).  This had become worn and imprecise, so a new rod was made with an improved design for the stops.
Two new levers.  One old lever.  Two refurbished levers.
Once the improved gear is in place, another attempt will be made to start the engine.
Top view of the engine with new Spragging Gear in place.

Filters

The original Ruston 4VRH engine had mesh/felt filters for oil and fuel.  These filters are not very effective and are messy to strip and clean.  A decision was made to replace them with modern cartridge filters, which are much more effective and because they are easy to change they are more likely to be changed regularly.  An additional water trap was installed on the fuel line as fuel quality cannot always be guaranteed.
New Water Trap and Fuel Filter
In order to make things as original as possible, the upper parts of the filter brackets were retained and adaptor plates made to accommodate the new screw-on filter elements.  The Ruston manual calls for an SAE20 or SAE30 detergent oil for the engine, and the use of a modern oil filter means that modern oils can be used – in this case Morris ring-free XHD30.  Diesel engines generate quite a lot of carbon past the rings and into the sump, so a good detergent oil keeps this in suspension and prevents sludge building up.
The new Oil Filter

Radiator & Fan Belt

The radiator consists of three parts; the upper tank (steel), the core (steel) and the lower tank (brass), which are bolted together with rubber gaskets.  Fortunately the steel core seemed to be OK after cleaning up.  New gaskets were made and the radiator tested for leaks.  The bottom tank was found to be leaking around the bolt holes.  This was traced to hairline cracks in the brass, and these were repaired by brazing.  The inlet and outlet pipes were badly corroded inside, and were not particularly well soldered. so these were replaced by new stainless steel pipes.

Subsequently the filler pipe started leaking around its joint with the upper tank.  It is vulnerable while the radiator cowl is not fitted and had probably been strained.  It was found to be rather crudely soft-soldered to the tank with only a steel wire ring underneath for support.  Because the pipe itself was badly corroded inside, it was decided to replace the pipe and secure the new one using large brass nuts and sealing washers.  The original filler cap was worn and would only engage on a few threads, so a new one was machined out of brass.

The original reinforced rubber hoses were replaced with new polyurethane hose, which is much more durable.  It was decided to incorporate a water level indicator.  This consists of a standard steam loco “gauge glass” tube contained in a machined brass holder and has been fitted next to the thermostat.
Radiator, water gauge and fan belt
The fan belt has been fitted and tensioned.  The belt is of the “link belt” type because it would not be possible to fit a standard belt without removing the bevel gears on the front of the crankshaft that comprise the hand winding mechanism.  In any case, the pulley profiles are of an obsolete type, and modern belts would not fit properly.  Indeed modern link belts are of the wrong profile too, but some suitable “Brammer style” link belt was obtained from Stationary Engine Parts.

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