Lightened Flywheel and Crank pulley

[maytag]

the TC motor is balanced internally, so the crank pulley isn't an issue...

Are you sure about this? I've seen several crank pulleys off Spiders, and they all have varying numbers of 5mm drilled depressions on the back side of the innermost pulley. Sure looks like a factory balancing technique.

Yes, factory balancing technique of the flywheel. The 180 d. Crank its inherently balanced, and the fiat crank comes from the factory balanced to the reciprocating assembly. But this means that your flywheel (and crank pulley) need to be balanced to neutral.

[Daniel]

You should read Crofts' book about flywheel lightening, too much material removal will result in a much-shortened life.

The issue with crank bearings going bad wouldnt be from light flywheels the source of this problem is
a crank pulley being to light lacking the stability from Inertia under high RPM loads to absorb vibrations
on the outer end of the crankshaft .

[opus10583]

You should read Crofts' book about flywheel lightening, too much material removal will result in a much-shortened life.

The issue with crank bearings going bad wouldnt be from light flywheels the source of this problem is
a crank pulley being to light lacking the stability from Inertia under high RPM loads to absorb vibrations
on the outer end of the crankshaft .

So a lightened pulley has to be tuned to the torsional resonance of the crankshaft?

How is this effected?

And, can I replace the crank pulley on a FIAT TC without disturbing the timing belt?

Thanks,
Mark

[coise]

WOOO,
I just ordered an aluminum cranck shaft pulley from Miller´s mull with a smaller diameter so my alternator won´t be overspeeding anymore (the light was going on and off above 5000 RPM).
Do you think it´s going to affect the balance of the cranckshaft?
If so, how do you balance it and Who can do that?

[maytag]

WOOO,
I just ordered an aluminum cranck shaft pulley from Miller´s mull with a smaller diameter so my alternator won´t be overspeeding anymore (the light was going on and off above 5000 RPM).
Do you think it´s going to affect the balance of the cranckshaft?
If so, how do you balance it and Who can do that?

No, no need to balance it, because Miller's Mule already has. Yes, you COULD send it in and have it dynamically balanced with the rotating / reciprocating assembly, but theoretically, no change would be made to the pulley.

I have an alu crank pulley and lightened flywheel coming from Miller's Mule (any day, I hope! ) as well. I am taking them in with my assembly to be balanced, but only because I have lightened / match-balanced my new pistons and the factory rods, so my crank needs to be balanced to them. My machinist will balance the entire assembly together. Again, he probably will not touch the pulley or flywheel.

And Opus, it's not about balancing to torsional anything. remember when you were a kid and you'd make snakes out of playdough? Rememebr that if you rolled it between your hands fast enough, the "top", where it protruded from your hands, would bend and deform? Think about the steel crankshaft in the same way. There is a certain amount of weight hanging out there on the end of the crank, unsupported. There is a rotational frequency at which that "nub" wants to start doing the same as the snake. This is typically absorbed into the damper (sometimes incorrectly called a dampener). When you remove that weight, the damping qualities change, and there is the possibility of harmonics becoming an issue.
IF you are building a motor that you expect to last you 100,000 miles or so.... don't use the lightened pulley. It may or MAY NOT cause a problem.