Sprinter Units share a common drivetrain, being alternator [not 158] – driveshaft – engine – cardan shaft – gearbox – cardan shaft – master (inner) final drive – cardan shaft – outer (slave) final drive.

The engine is a 6-cylinder, 285 bhp Cummins NT855R5 unit fitted roughly halfway along the vehicle, with an idle speed of 600rpm and a maximum speed of 2100rpm when vehicle fully loaded and 2400rpm when vehicle empty.

• On class 158 units the engine is uprated to 350hp by use of an intercooler between the compressor and engine which cools the (hot) compressed air allowing higher rate input and thus higher speed of engine operation.
• Certain class 158 units (numbered in the 8xx series) are fitted with a Perkins engine in place of the Cummins unit.

The gearbox is a Voith T211R Hydraulic transmission, consisting simply of a Torque Converter, Fluid Coupling and Control System. The Torque Converter is used for starting and low speed running up to about 40 mph. The Speed Shift Governor will then operate and cause oil to empty from the Torque Converter and fill the Fluid Coupling. When engine idling all oil is drained from the gearbox and there is no drive transmitted from the engine to the final drives.

Final drives are manufactured by Gmeinder and are driven by the cardan shafts from the Voith to the master final drive and thence by a second cardan shaft to the slave final drive. Both final drives are permanently engaged in gear; no isolation or reversing mechanism is supplied or necessary.

Batteries: there are two sets of 24v batteries on Sprinter units – Start and Auxiliary. Except on 153s, Auxiliary batteries are located on the nearside of the vehicle; Start batteries on the offside. Battery Isolation Switches (BIS) are provided for each set of batteries, and should be left ‘ON’ (handle vertical) unless otherwise instructed.

• The Auxiliary Batteries supply power for all lighting, for the Webasto heater and also to operate the bottom row of MCBs, including Door Supply. There is a Low Battery Volts Protection Device fitted which will operate at 22.5V and will cut out all lights including frontal lights – but not the Webasto heater which will flatten the battery if left running and must therefore be isolated when units are stabled.
• The Start Batteries provide the supply to start the engine, to all controls and the desk, to the TCA and AWS, and to the top row of MCBs including Door Control. There is no low voltage protection fitted as supply can be obtained remotely from other vehicles.

Alternator: Supplies 28V to charge both sets of 24V batteries.

• If failed, Engine Stop light will be bright, but all engines will still run. Engine on affected vehicle will revert to idling; use Compressor Speed Up and check all engines. Locally shut down and isolate affected engine. Note that aux. Battery is not now being charged; lights will extinguish after approximately 30 minutes.

The diesel engine used is a Four Stroke engine, the cycle being Induction – Compression – Power – Exhaust.

1. Induction – Piston Down, sucks air into cylinder;
2. Compression – Piston Up, Compresses air, heating it;
3. Power – Fuel injected, mixture explodes (resultant temperature about 4000°C), piston forced down, power transmitted to crankshaft;
4. Exhaust – Piston up, exhaust gases forced out via turbocharger to atmosphere.

The engine has 6 cylinders fitted ‘in-line’, meaning that all 6 cylinders are attached to the same crankshaft. There are 3 visible cylinder heads, each covering 2 cylinders; each cylinder has 2 inlet, 2 exhaust and 1 injection valve, operated by used of 3 rocker switches attached by pushrods to the camshaft, which runs at half the speed of the crankshaft. The valves are sprung to return them to the closed position. The firing order of the cylinders is 1,5,3,6,2,4.

Turbocharger: Operated by exhaust gases from the cylinders, this draws air in from atmosphere to feed to the cylinders. The turbine blades and linked compressor blades run at speeds of up to 25000rpm.

Lubricating oil: Oil is pumped by a camshaft driven, externally mounted pump from the sump through two Pump Pressure Relief Valves at 140psi and 45psi respectively, then through the Oil Cooler Thermostat Valve (Bypass Valve), which opens at 96°C and is fully open at 112°C, to the Oil Cooler (at lower temperatures bypasses the cooler) and thence to the Oil Filter. From there oil will pass through the galleries to lubricate the compressor, turbocharger and bearings via drillings in the crankshaft. It will eventually leach back to the sump.

The 140psi PPR valve guards against abnormally high oil pressure, for instance when starting engine during very cold weather.

When the engine is hot, oil pressure should be 10psi at idling and 45psi when under power. The absolute minimum is 8psi at which point the Oil Pressure Switch will operate, closing the Engine Run Solenoid and shutting down the engine.

Fuel System: A 400 gallon fuel tank is provided; Capacity is actually 450 gallons but space is left for fuel expansion when heated. Fuel is pressurised at 300psi, and is drawn from the tank by the fuel pump (driven by the engine at engine speed) through the filter and pump and thence through the governor unit, which runs at twice engine speed and controls engine speed by blocking fuel line to control fuel supply to the engine. From the governor it is fed through the idle and main passages to the Throttle Control Unit, where 4 valves control supply through the Engine Run Solenoid to the injectors.

The throttle control unit consists of 4 EP valves, A, B, C and D, which are energised by the drivers power controller and give a total of 7 combinations of fuel supply to the engine and thus seven power settings.

These are:

Engine Cooling: Coolant is pumped around the engine, the engine and transmission cooling system and also the vehicle heating system. If there is insufficient coolant in the header tank, this will be detected by the Mowbury Float Switch which will de-energise the ERS and cause the engine to shut down.

The coolant system is pressurised at 12psi and has a capacity of 17.7 gallons. This is pumped round the system at the rate of 7000 gallons per hour.

To ensure coolant runs at the appropriate temperature, the Webasto cuts in at 72°C and cuts out at 78°C. The thermostat starts opening at 78°C and is fully open at 95°C, allowing water to pass to the radiator to cool. At 88°C the Fan Drive Control Unit starts to allow hydrostatic (Serck) oil to the fan motor to run the radiator fan; this will be running at its fastest at 95°C and above, when it will reach approximately 3000rpm. At 96°C, the High Water Temperature Switch will operate and the engine will revert to idling.

The coolant system also provides train heating with hot coolant passing through the saloon heater units. Fan motors blow air over the coolant pipes, heating the air which is blown into the saloon. Isolating Cocks are provided for the Heater Feed and Return pipes, and an MCB is provided for the Saloon Fans.

Air system: Each vehicle has an engine run compressor that supplies air to the Main Reservoir Pipe and thence to the brakes, doors, suspension, horn, wipers, martonair box and so on. The compressor runs continuously and is unloaded when the air supplied is not required. Minimum air pressure is 4.4 bar (@64psi); if pressure drops below this the brakes will apply.

When building air pressure, the Low Main Air Governor will hold the brakes on until 5.5 bar (@80psi) is reached, and will apply the brakes at 4.4 bar. The unloader valve will operate at 7.6 bar (110psi) and will close at 6.6 bar (@95psi), thus maintaining system air pressure at between 6.6 and 7.6 bar. Safety valves are fitted, one before the unloader valve rated at 9 bar and one between the unloader valve and the main reservoir rated at 8.3 bar. In the event of an unloader valve failure, an isolating cock is fitted.

Main res. air is supplied through the train by through MR pipes, protected by star valves fitted to the pipe on the coupling. MRP isolating cocks are fitted to isolate the vehicle.

Numbering of wheels: Wheels on sprinter vehicles are numbered, starting at the secondmans side of the cab (no.1 end of class 153) with wheel 1 and working clockwise around the unit to wheel 8 under the driver.

• Parking brake operates on wheels 2 and 8 only of each vehicle, except on class 158 units where it applies to wheels 1,2,7 & 8. They are fully released when Main Air pressure reaches 5.1 bar (74psi).

• Speed Sensors are fitted to wheels 3 and 7. If greater than 7% difference in axle speeds sensed, wheelslip (WSP) will operate, returning engine to idle and operating WSP light [Gearbox Train light]. When WSP ceases, power will be restored without the need to reset the power handle.