On 2 Jul 1998, Pat B wrote:
> Crankshaft unbalance for the inline six cylinder is not a typical
> vibration issue, however
Remember that these engines are pretty basic and crude affairs.
Presumably built to generous tolerances when new, and definitely not
getting any better through DPO bodges. Piston and conrod imbalances of 30g
are not uncommon - this makes even an inline six pretty rough even at
modest RPM. Especially on the 2.5: The long stroke in combination with
four main bearings of modest diameter cannot possibly be a recipie for
crankshaft rigidity.
My guess is, then, that for the average owner mass imbalances are
probably a worse problem with respect to vibrations and decreased engine
life than inherent resonances.
> The problem occurs when the firing frequency and the resonant frequency
> are the same.
Thanks for a very clear explanation.
But as explained, I would imagine that your figure of 300 Hz cannot be a
constant, and would depend entirely on the mass and geometry of the
crankshaft.
It is worth noting that the damper for the 2.5 litre and the shorter
stroke 2 litre six are different. Presumably because the two crankshafts
have a different resonant frequency.
> Regardless of the phenomena involved, DO NOT remove the crankshaft
> damper!!
We all agree on that. And also, presumably, that the fan, even if mounted
at the end of the crankshaft, does not contribute significantly to the
prevention of crankshaft vibrations.
Egil
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