Quietening the Fleetline
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DELIVERY is expected to take place soon of the first Daimler Fleetline doubledecker to have a "quiet" engine installation to London Transport, The first prototype vehicle was shown to the technical press in Leyland last week. A mock up of a chassis with an encapsulated engine was first shown at the Earls Court Show.
One of the main features of the quiet programme -designed to achieve a driveby noise level of 82dB(A) — is the use of the Leyland 690 engine.. This is. a turbocharged version of the 680 not normally offered on the British market which is derated to produce no more power.
Because of the Variations in dimension of the various bodies fitted to the Fleetline by bodybuilders, I.eyland has opted to retain the separate engine pod at the rear, rather than adopt air inlets and outlets in the body sides as Bristol has done.
A 5 72 mm (22IA in) diameter fan is mounted below an inlet vent on the offside of the.vehicle.The fan is in cast alloy and is designed to reduce. vibration.. It is hydraulically driven at a constant speed and draws in air through a grp ducting system.
The air is blown through a new larger radiator mounted at a slant and then across the top of the engine and out through a vent on the nearside. A 280 mm (II in) diameter air filter is used which is claimed to give increased element life. Air for the filter is drawn in through a slot imMediately behind the lower saloon rear window.
The engine is encapsulated by three double-skin panels across the bottom of the engine compartment which have quick release fasteners: In a further bid to decrease noise an in line pump is used in place of a DPA unit.
For the first time Leyland has specified a hydraulically driven alternator which is mounted on the gearbox casing so that it is both in the airflow and easily accessible. The hydraulic reservoir is mounted in tfie air outlet vent so that it is kept cool.
Basically, the same treatment will be applied to Gardner-engined versions of the Fleetline though the target noise level is 2d B(A) higher.at 84dB(A).
Production of quietened Fleetlines is expected to get underway in the middle of next year when encapsulation will become a standard feature. Leyland engineers report that a similar treatment may well he applied to the Atlantean chassis which otherwise could become the only Leyland double-decker without the "quiet" treatment.