When the bigger diesel hydraulic locomotives were designed technology was still being developed. Although the Westerns were built from 1961 onwards the transmission design went back to the middle 1950's. At that time the maximum 'input' (the power from the diesel engine) that any single transmission could manage was around 2,000hp. Therefore to have a locomotive more powerful than 2,000hp required two smaller transmissions, each with its own engine.
The twin engine 'reliability' was more by default than design. By the time that the Westerns were actually built technology had overtaken them and transmissions with a bigger capability were already being constructed. Just like today when you buy your new computer, it its already out of date by the time its on the shelf!
When
a transmission changes gear the physical connection between the transmission and
final drive to the intermediate gearbox is momentarily broken by a clutch known
as a 'dog' clutch. This clutch has a 'male' and 'female' side and to 'mate'
properly the teeth on one side need to fit inside the other. On occasions the
teeth will try to mate face to face (tooth on tooth) and the operation of this
button pushes the clutch around until the teeth fit inside each other properly.
Sometimes
in your car you misjudge the gear change and you hear that awful grinding of
gears. If your car was a hydraulic you could press the tooth on tooth button and
the gears would mesh correctly, instead you just dip the clutch and try again!
Did you know that when a twin engine diesel hydraulic locomotive moves forward the rear transmission is in reverse! This is because the Maybach diesel engine rotates clockwise when running at the flywheel end. If both transmissions were in forward the locomotive would try to pull itself apart! Gear changes between the two transmissions also take place at different speeds. The leading transmission changes first, followed by the trailing one. This is to reduce the risk of the locomotive causing a 'snatch' in the train and breaking the train couplings.
No, the engines are not sick! The turbo charger that compresses air and pumps it into the cylinders, along with the fuel, is driven (rotated) by the exhaust gases from the engine itself. When the engine takes power from idling the turbo blower is 'lagging' behind (turning slowly) and the fuel / air mixture is more in favour of fuel until the turbo charger speeds up and pumps the air in faster. Once the turbo charger is rotating faster the fuel / air mixture is corrected again and the exhaust emissions clear. This is called 'turbo lag'. You can clearly hear the turbo charger working hard on a Maybach, it’s the whistling sound as the engine revs pick up.
In
order to aid starting a Maybach diesel engine the coolant water is warmed to 1100F
(around 430C). This warms the cylinder heads and helps combustion of
the diesel fuel oil. The combustion of the fuel and air mixture takes place
inside a chamber within the cylinder head and then expands into the cylinder
itself, forcing the piston downwards. The characteristics of this engine type
doesn’t lend itself easily to cold starting. Warmed engines start more easily,
should run cleaner with the added bonus of reduced wear and deposits (carbon
etc) associated with cold starting of any diesel engine.
There
are a number of unique advanced features incorporated in a Maybach MD series
diesel engine such as pressure oil cooled two piece pistons, roller main bearing
crank shaft, quadruple overhead camshafts, six valves per cylinder head (3
valves air inlet and 3 valve exhaust gases) and a individual pump / injector
unit per cylinder.
The
engine coolant is warmed by a small preheater, located in a compartment behind
the cab side doors at each end. The preheater only runs prior to starting or
when the engines are shut down and are getting 'cold'. You can hear them running
sometimes when we shut down the engines at stations. It carries out the same
purpose as glow plugs do in modern diesel engine cars.
Although it is possible to 'cold-start' a Maybach engine it is not recommended.
Some sites on
the internet have held articles about tours from Paddington always stating that
the departures were always sedate. Well, there is in fact a very good reason for
this policy. The coolant system on a thousand gets very hot very quickly and
storming out of Paddington on full power on a relatively 'cold' engine would
cause the coolant water to heat up quickly and expand (water expands when
heated and this creates the pressure) and there is a risk that the coolant
pressure relief valve could 'lift' and the coolant would be thrown out. This
means that the engine would then probably fail with low coolant and we would
either spend the rest of the trip operating on one engine or become a total
failure until the coolant could be refilled.
In
B.R. days of
course the locos engines ran constantly and this was not too much of a problem.
Once the engine coolant has had time to fully circulate around the system then
full power can be applied. It normally takes around four or five minutes for
this to happen.
The
technical design of the Western diesel hydraulic locomotives was taken from a
German Railways built C-C locomotive type ML3000. This locomotive was a
stretched V200 B-B locomotive giving 3000 hp and weighed just 101 tons.
So
why were Westerns heavier at 108 tons?
Well, originally it was envisaged that the Westerns would be more powerful versions of the Warships with the same internal layout, i.e. engines behind the drivers cab. This did not meet with approval from the drivers and unions as the constant noise and vibrations from having a diesel engine thrashing away directly behind you made driving Warships a very noisy occupation. In order to remedy this the engines were placed in the middle of the body with the cooler groups behind the drivers cab. This meant that the frames in the middle of the locomotive had to be thicker and stronger to take the weight of the engines. Even so the designers put a bend upwards in the frames, and this bend straightens when the engines are mounted. Therefore when a Western has its engines removed the loco bends upwards like a banana! The deflection upwards is around 3 inches, making an empty Western out of gauge for running on the main line.