The dual-mass flywheel or DMF is actually a great piece of engineering. The imagination used by it’s original designer has proven itself so worthy not only in the performance of the engine to gearbox transfers of torque but this stroke of ingenuity has more so been a success due to it’s reduction in the vibrations that a diesel or petroleum engine normally transmits to the gearbox of the motor vehicle.
This relatively new piece of equipment has been a ‘must have’ fixture to most modern day engines as standard equipment which also comes with a downside and that is unreliable and expensive.
Any engine that is properly balanced is prone to vibration in a number of ways. These vibrations are almost impossible to eradicate due to the repetitive and stringent combustion forces acting on the pistons, con-rods and crankshaft at regular intervals as per the firing order of a particular engine.
The most damaging of these vibrational modes experienced is torsional and the effect gets worse at the lower engine RPM range or at open throttle operation. Diesel engine vibrations are up to four times more severe under the rotational and pressurized conditions than that of most petrol engines.
There are many designs of the now common DMF which is assembled by adding two flywheels together instead of one flywheel. These discs are about the same diameter as a single flywheel would be but half the thickness, so each one will have less than half the mass of a single flywheel. The first flywheel is attached to the crankshaft and spigotted into the second flywheel in such a way, that the two discs are able to oscillate in respect with one another.
The rotational movement is controlled by ‘circumferential springs’ working against stop ends so that the first flywheel is able to harmonically vibrate with the rotations of the crankshaft while the springs ensure that the least of these primary vibrations get transferred to the second flywheel. Then an almost normal clutch unit, but without springs in the hub of the driven plate is bolted to the second flywheel and the gearbox input shaft is splined to the driven plate.
The result of this set up means that the usual torsional vibrations that a conventional clutch and flywheel gets is harnessed and dampened by the springs that are not transmitted through the gearbox, and to the remainder of the motor vehicles drivetrain, which ultimately results in a smoother running engine and clutch action.
Unfortunately, the DMF units on some vehicles are not as reliable as they should be as some of these units give in at mileages below the warranty of 100,000 km. DMF replacement is far more expensive than the old conventional single plane flywheel and clutch assemblies.
An alternative replacement is available whereby a newly weighted single plane flywheel is machined from either billet steel or extruded aircraft aluminium and fitted with a quality clutch kit, which is reliable and which works.
Contact LOOKING 4 SPARES on 0861-777722 for more info on FLYWHEELS and CLUTCH KITS www.looking4spares.co.za/parts-request