what is the rubber ring in crankshaft pulley?

[gumby]

is it

A.) a balancer

B.) a dampner

C.) for the power stroke

D.) for the ac compressor

E.) all of the above

F.) just there to piss me off

[navysnail]

it is a dampner for when you turn on the ac, so it doesnt engage as harshly putting undue strain on the engine and compressor.

[DAEDALUS]

Why, did you tear it?

The rubber ring is a torsional damper. A large misconception is that dampers aren't needed when engines are internally balanced. But "internally balanced" has nothing to do with torsional harmonics. Without a torsional damper, crankshaft stress increase and can lead to premature failure of the crank (fatigue). Failure can be very quick if the engine is revved through critcal frequencies. Fortunately for you, the crankshaft on 4-cylinder engines is short enough that harmonic frequencies only exist well above redline. This is why you can often get away with using aftermarket underdrive pulleys without dampers.

Edit: I could be way off on this. Usually rubber rings on the crank pulley serve as torsional dampers, but I don't know for certain on that particular engine.

[navysnail]

there was a discusion on this in another thread somewere but i dont remember, the consensus was that it is there for the ac and that many people who have had aluminum underdrive pulleys for thousands or miles have had no problems.

some of the harmonic balancers for say, big block v8's are absolutely nesesary but as DAEDALUS said, on the 4 cylinder, it is not completely necessary

[s13sr20chris]

hmmm, thats interesting. i have always been told that nissans are internally balanced yet the crank pulley on most performed some sort of balancing duty(other than the vq series). i may have been mislead. this all stems from a lack of knoledge on just how harmonic balancers work.

[gumby]

oh great, even the gurus dont know

[DAEDALUS]

hmmm, thats interesting. i have always been told that nissans are internally balanced yet the crank pulley on most performed some sort of balancing duty(other than the vq series). i may have been mislead. this all stems from a lack of knoledge on just how harmonic balancers work.

Counterweights are used to balance vibrations of the shaft...those you can feel when you touch an unbalanced engine with shot mounts. I believe you're right that I4 Nissans are balanced in this respect.Torsional harmonics deal with frequencies in rotation about the shaft, from the power stroke every 180*, separated by a time during which the shaft "unwinds" from the stresses of the last power stroke. These twisting harmonics can't be "balanced"--they can only be damped out if they get too close to a critical frequency (or design for a higher critical frequency with a thicker shaft or better material).

[navysnail]

kind of like how that rusty exhaust heat shield resonates at that certain rpm each time, same idea

[gumby]

essentially it twists

[navysnail]

thats why i think we came to the conclusion that it dampens the engagement of the ac compressor, because it twists a little and gives it a "cusion"

[Nismo_Freak]

thats why i think we came to the conclusion that it dampens the engagement of the ac compressor, because it twists a little and gives it a "cusion"

Supercharger pulleys aren't dampened.

Honestly I think your thesis has little bearing on the reasoning for the dampened pulley.

Daedalus is 100% correct on the reasoning for the dampened pulley.

[s13sr20chris]

heh, funny! i have at one time learned all of that but i was confusing torsional harmonics with vibration. for some reason i was thinking that dampening was just a cheap shortcut to balancing but they are totally separate issues. whew, glad i have a beast of a crank now! thanks daedalus, you did an excellent job of explaining that.

[gumby]

alright so bottom line is i want to keep the stock pulley if im concerned with enigine life cause its dampened. yes?