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lightend crank pully??
Krismc - 14/5/06 at 05:06 PM

I have a lightend flywheel and ive been offered a lightened (aly) crank pully! will i recieve any benefits and will my engine be ok with both these on!

flak monkey - 14/5/06 at 05:21 PM

Crank pulley had little effect on the rotational inertia of the system due to its small diameter.

Up to you if you want to fit it. You cant see it when it is on there anyway

Benefits are negligable and the engine will be fine with or without it.

Krismc - 14/5/06 at 05:25 PM

well i wont bother then!!

cheers for that mate

ned - 14/5/06 at 09:05 PM

i have one (ally front pulley) but unecessary expense really, unless you're lightening and balancing the whole crank, flywheel and clutch as i have but still negligable unless you want every last hp out of it.

Ned.

ps mine is also a smaller diameter so it actually has even less effect when spinning as flakmonkey says, but it also reduces the charge to the alternator

MikeRJ - 14/5/06 at 09:24 PM

If the oringal crank pulley contained a crank damper and the shiny new one doesn't then one of the differences you may notice is shorter crankshaft life!

[Edited on 14/5/06 by MikeRJ]

02GF74 - 15/5/06 at 09:01 AM

quote:
Originally posted by MikeRJ
If the oringal crank pulley contained a crank damper and the shiny new one doesn't then one of the differences you may notice is shorter crankshaft life!

[Edited on 14/5/06 by MikeRJ]

how come?

my understanding, wrong it may be, is that is reduces shock to the drive belt.

as for fitting it, there a no increaes in power, just like when fitting a lightened fly wheel; the difference having less mass to spin up to speed meaqns the engine will reach that speed quicker.

unless it is free or less than £5, don't bother.

MikeRJ - 15/5/06 at 10:34 AM

quote:
Originally posted by 02GF74
my understanding, wrong it may be, is that is reduces shock to the drive belt.


No, a belt drive has inherent shock/vibration absorbtion, no need for any other damping. The crank damper is so-called because it is used to dampen torsional vibrations in the crankshaft.

As with all components the crank has a natural resonant frequency, and once the engine speed hits that frequency the amplitude of the vibrations can increase significantly which can dramaticly shorten the fatigue life of the crank. It can also reduce power as the cylinders furthest from the cam drive (belt/chain or gears) will be seeing timing variations as the crank twists.

Generaly, the longer the crankshaft, the worse the problem becomes.

NS Dev - 15/5/06 at 10:59 AM

Quite right!!!!!!!!

Torsional vibration on the crank is very severe!!!

one of the common problems on the vauxhall xe engine is shattering the oil pump inner gear which sits on two flats on the crank nose.

This happens if the locking bolt that pinches the gear against the shoulder on the crank comes loose, then the torsional vibrations chafes then shatters the gear!!

If you want a demo of the effect, try holding onto an extension bar on an air impact wrench. That's what the engine crank is going through basically!