Aluminum ABY Crank & Alternator Pulleys

[Rusty]

Is the 'For Sale' section the right place to discuss, yet again, the issues relating to different pulleys, FWs, balancing and harmonic vibrations? Perhaps move this to a thread in the engine section where it won't get lost?

[driftin jo]

Another good link on the subject for you to have a read of when you have read the links in post #9.

http://www.atiracing.com/products/dampers/damper_dinan.htm

[terrybullwon]

I will say this once more listen carefully "IT HAS NOTHING TO DO WITH BALANCING"

Please read post #9 and the links that i added for ref.

Hes right, Go buy a engine building book. It will say the same.

I sold my aluminum pulley and replaced it with a OEM one

Even though my whole engine is blanced.

[Rusty]

Thanks for the links there Jo, an interesting read.

So basically the vibration damping effects of the OE pulley is designed for a completely stock crank, flywheel, pistons, rods etc. As you start to mess with the components the resonant frequency of the system changes and thus the vibration damping effect of the tuned front pulley will become less effective as it is not longer tuned to the correct frequency, in some cases it could even lead to reinforcement of the destructive waves, should the resonant frequency and tuned frequency coincide in such a way. So for any modified crank setup you should have a new design of torsional damper to ensre that it is correctly tuned... it's alos worth noting that the damping of the OE rubber pulley only works effectively at one frequency and not at all subsequent orders.

[MikeLarwood]

So basically the vibration damping effects of the OE pulley is designed for a completely stock crank, flywheel, pistons, rods etc. As you start to mess with the components the resonant frequency of the system changes and thus the vibration damping effect of the tuned front pulley will become less effective as it is not longer tuned to the correct frequency, in some cases it could even lead to reinforcement of the destructive waves, should the resonant frequency and tuned frequency coincide in such a way. So for any modified crank setup you should have a new design of torsional damper to ensre that it is correctly tuned... it's alos worth noting that the damping of the OE rubber pulley only works effectively at one frequency and not at all subsequent orders.

Partially, but not entirely, correct. A damper isn't necessarily 'tuned' - given it's application and the fact that every crank can have a slight variance on it's resonant fequency, the pulley will just be an unintelligent damper. The use of rubber in the design proves this, as does the fact that cranks can have various critical frequencies that could cause a fracture.

[Rusty]

Guys, I've created a new thread here as this is important information that should be in a more public forum

Thanks Mike, my knowledge on this sort of thing is limited to first principles from uni, if I understand you correctly, small changes to the crank will result in changes that the damper can tolerate, larger changes, such as extremem weight reduction might be outside of tolerance. Also, what effect does flywheel weight have in all of this, does a heavy flywheel mean that the free end of the crank takes more movement than a more equal FW to pullety weight?

[driftin jo]

So basically the vibration damping effects of the OE pulley is designed for a completely stock crank, flywheel, pistons, rods etc. As you start to mess with the components the resonant frequency of the system changes and thus the vibration damping effect of the tuned front pulley will become less effective as it is not longer tuned to the correct frequency, in some cases it could even lead to reinforcement of the destructive waves, should the resonant frequency and tuned frequency coincide in such a way. So for any modified crank setup you should have a new design of torsional damper to ensre that it is correctly tuned... it's alos worth noting that the damping of the OE rubber pulley only works effectively at one frequency and not at all subsequent orders.

Wrong !
If you change the rods / pistons the resonant frequency of the crank will not change, it is not the resonant frequency of the system just the resonant frequency of the crank that the pulley is damping.
your non stock components may be more likely to set off the resonant frequency of the crank as they normally go hand in hand with more power!

The only way the pulley would no longer be effective is if you were to remove a lot of material from the crank itself, this is why the people in the know don't do this either !

[Rusty]

Wrong !
If you change the rods / pistons the resonant frequency of the crank will not change, it is not the resonant frequency of the system just the resonant frequency of the crank that the pulley is damping.
your non stock components may be more likely to set off the resonant frequency of the crank as they normally go hand in hand with more power!

The only way the pulley would no longer be effective is if you were to remove a lot of material from the crank itself, this is why the people in the know don't do this either !

Right, I think I'm getting the picture now, just like to ask questions, even if I am wrong . I've moved the relevant quotes to the new thread, please can we discuss it there? Copy and paste is wearing out on my computer

[MikeLarwood]

The only way the pulley would no longer be effective is if you were to remove a lot of material from the crank itself, this is why the people in the know don't do this either !

So does this mean taking material from the crank (knife-edge?) could cause this issue? Or is this not sufficient material?

[Rusty]

Please can you post up on the new thread Mike?

[MikeLarwood]

Spotted, done.