Why is it better to have the springs on a bi-mass flywheel than on the clutch plate?
When a bi-mass flywheel starts going wrong it starts to shudder and vibrate. Why is that?
Short answer:
because the long specially wound springs in the flywheel are broken and your flywheel is no longer stopping the TORSIONAL vibrations from the engine from being transmitted into the other driveline components. (Steve67 explanation is unfortunately wrong !)
Long answer:
the springs do NOT push weights outboard!!!!
2 mass flywheels were introduced into cars when the tdi engines started to produce massive amounts of torque, compared to petrol or non-tdi diesel engines, at low revs. The increase in torque also came with an increase in crankshaft torsional vibrations.
In the past, pre tdi, manual gearbox drivetrains had two systems of reducing the torsional vibration being passed onto the gearbox and drive line.
1) a torsional vibration damper mounted at the front of the crankshaft, this had an outer mass (which drove the alternator etc) and was connected to the crankshaft by a rubber ring. The outer mass and rubber stiffness were "tuned" for each engine to reduce the torsional vibrations of the crank to a minimum.
2) a torsional vibration damper was also incorporated in the clutch plate ( the little radial springs). These dampers were also tuned for each powertrain.
Automatic cars with "slush" torque converters eliminated the torsional vibrations from being transferred. Later auto boxes with lockup also have a clutch plate with a torsional vibration damper (in use when locked up).
When tdi engines were introduced they initially (before two mass flywheels) had gearbox noise problems, "razzeln", which could easily be heard in the car and was frequently complained about by customers. The "razzeln" was caused by the torsional vibrations (if you have ridden a single cylinder motorbike they also "razzeln" at low engine revs).
Possibly the torsional vibrations also caused pitting on the gears and other driveline durability problems.
The two mass flywheel uses the long springs, mounted at a constant circumference, and second mass to "disconnect/isolate" the engine torsional vibrations from the gearbox. The spring stiffness and flywheel mass are "tuned for each engine".
A bit like a LINN turntable uses springs to isolate vertical vibrations, or speaker isolators.
When you replace the two mass flywheel with a conventional flywheel you allow the "torsional" vibrations to pass down the drivetrain and create other problems. You will probably find that the original clutch plate used with a two mass flywheel does not have any springs in it (doesn't need the springs as the vibrations have already been isolated).
If you replace the two mass flywheel then you should use a cluch plate with springs that has been "tuned" to try and reduce a portion of the vibrations passing down the driveline.
Perhaps the car manufactuers have on two mass flywheel applications also eliminated the old front mounted crankshaft damper to reduce costs (the old front mounted crankshaft dampers were only fitted on large capacity engines). This would also mean that when you remove the two mass flywheel high levels of vibrations are being passed down the driveline.
Hope this helps.
