Pulley question...

[stinkysGTI]

While I was waiting for my ECU to be flashed, I started talking to a guy who works at the place and we got into a "lightweight parts" discussion; one of the topics was pulleys.

He was saying it's NOT a good idea to change out your crankshaft pulley for a lightweight one because it's heavy for a reason. To counter-balance the crankshaft since it's already rotating on an off-axis kind of spin. It would be like spinning a broom with a heavier or lighter weight at the end and everything would start getting wobbly. It seemed like a pretty logical assumption, but I don't know if it would really effect it like that since it's being held in place by all the piston arm bearings.

What do you think?

[Mr_Diesel]

The crankshaft has near perfect balance in it's self. The whole purpose of the crankshaft's shape is to counteract the movement of the pistons. If your engine has a harmonic balancer (which it doesn't) it would be important not to change it out. IMO, a harmonic balancer is designed to make up for cheap engineering. I stole this from another site:


The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both. When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.The purpose of a heavy flywheel or crank pulley is to transfer the erratic and "explosive" movements from the engine into smooth energy. The problem with heavy rotating mass is your engine can't rev as fast. In formula one engines, you barely touch the accelerator pedal and engine is revving at 8,000rpm. Why? Cause they have virtually no rotating mass. Everything is light weight. This small rotating mass also enables the engine to safely rev to upwards of 12,000rpm.

To put a very long story short, light weight pulleys and flywheels are good. The disadvantage is you will loose some drivability. Very lightweight flywheel/pulley can make it hard to operate the clutch without stalling the engine. If you are a beginner with the manual trans, then you should probably wait a few years before making these mods. I think this guy you talked to must have been thinking of engines with harmonic balancers which is irrelevant with our cars. But anyway... are you talking about lightweight pulleys or UNDER DRIVE pulleys?

[zukgod1]

Mr Diesel nailed it.

Sounds to me like the guy your talking to is thinking of V8 engines and the like.
As Mr Diesel pointed out light weight pulleys are good on our cars but do take some getting use to as far as drive ability goes. Although I doubt you would notice a difference changing just one pulley.

[stinkysGTI]

That made a lot of sense, thanks Mr_Diesel. I'm just talking about the lightweight pulleys. Alternator, power steering and crankshaft. What type of drivability issues will there be?

That guy, yes, was probably talking about bigger engines. He's the BMW guy at the shop.

About the flywheel, I was gonna be getting a flywheel/clutch kit in a couple of months and I think I have a lot of experience with manual. I've owned 4 vehicles and all were manual, except one was auto for a few months, then my dad and I converted it to manual. I also worked as a valet for 4 years so ya know, that entails driving the nicest to the ****tiest of rides. Recently I've been driving a sandrail which is a brute of a machine that needs to be manhandled :D

I don't think I'd have any problems that 5 minutes of driving wouldn't cure :)

[reinaldo]

It seems right that there should be weight counter balance for crankshaft so that it will be held in place for better function.
__________________________________________________ _______________

(http://www.carparts.com/Crankshaft-Kits-Accessories/600022780.car)