BS 5514/1.
MARINE ENGINES
The Thornycroft 90 and 108 engines are both 4 cylinder, 4 stroke naturally
aspirated high speed diesel units, both engines having electrically operated heater
plugs to aid cold starting.
The cast iron crankcase with ribbed sidewalls houses a forged steel, fully
counterbalanced crankshaft carried in three or five bearings respectively.
A full pressure wet sump lubrication system is employed with a full flow
detachable element type oil filter and integrated lubricating oil cooler.
The cooling system is indirect and usually employs an engine mounted heat
exchanger with a belt driven raw water pump. This system is known as IFWC
(internal fresh water cooled).
An optional system is EFWC (external fresh water cooled.) This system utilizes the
engine fresh water pump and usually employs skin tanks attached to the hull to serve as heat
exchangers.
The single belt driven alternator and fresh water pump drive include a manual
belt tensioning arrangement for low maintenance completes the comprehensive
engine package.
90 108
4 Cylinder naturally aspirated 4 Cylinder naturally aspirated
Power intermittent at 3500rpm = 36BHP Power intermittent at 3500rpm = 47BHP
2500rpm = 531bf ft
= 570rpm
Idle speed = 570rpm
Minimum full load speed = 1500rpm
ENGINE RATINGS
Minimum full load speed = 1500rpm
The type 90 Engine may be set to develop continuous outputs from 13.5 to 30 BHP according to
requirements
The type 108 Engine may be set to develop continuous outputs from 21 to 38 BHP
according to requirements.
For special applications where full power will not be required for periods in
excess of 1 hour in any 12 hours consecutive running the engine can be supplied at an
intermittent rating as shown above.
NOTE: All horsepower ratings quoted are at the engine flywheel. Due allowance must
be made for transmission losses which will depend on the type of gearbox fitted.
For tropical use it is necessary to derate the engine by 2% for each 5%°C (10°F)
above 30°C (85°F) air temperature at sea level. In some parts of the world
further derating for humidity is necessary in accordance with
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