Friday, Sep 11, 2015 at 12:42
Thanks for the
feedback, that is interesting. Essentially, there are only three ways (
well, four, because two are related) that drivetrain vibrations can be produced from a clutch, flywheel and crankshaft combination.
One way is from flywheel and clutch imbalance, which can be cured by removal and proper balancing of the complete clutch and flywheel assembly when imbalance is suspected or noted.
The second way is from a flywheel that is not running true (wobbling). Measurement of flywheel runout is a critical feature of engine building and overhaul - and one measurement that is often ignored during overhauls. A flywheel with excessive runout can be caused by either a buckle in the flywheel or a bend in the end of the crankshaft.
The third way is torsional whip in a crankshaft - a very common source of low-frequency drivetrain vibration. It is caused by poor crankshaft design with inadequate resistance to varying torsional stresses, and it can also be amplified by the material the crankshaft is made from.
The fourth way is less common today and is caused by longitudinal whip in a crankshaft. This is caused by inadequate crankshaft support and was more common in the days of inadequate numbers of main bearings - as in 3 bearing mains in 4 cylinder engines.
I can see where the clutch bloke is coming from, by talking about vibrations created by heavier solid flywheels.
Nearly all engines and crankshafts today are quite high-tech in their design and materials, and they are much much lighter than they ever used to be.
As a result, altering the weight of a component such as a flywheel can immediately create torsional whip problems in a crankshaft that is lighter than ever, and which has narrow design parameters than never considered a heavier flywheel.
I'm not sure about the 2.5L Mazda engine in your vehicle, but I know the new Ford Duratorq engines now utilise a forged steel crankshaft (which Ford claim is "lighter than previous models" - as always!).
A cast iron crankshaft has more weight and rigidity as compared to a lightweight forged steel crankshaft, and the steel crankshaft has a tendency to be "springy", thus creating the potential for introduced crankshaft torsional whip, if a much heavier flywheel is fitted than the original design intended.
Cheers, Ron.
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