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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
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| 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.
