Pulley Issues!!

wstar

Well, there's a lot of confusion on this issue about vibrations, dampening, and external vs internal balancing. I can't settle the matter for our engine, but I can clear a few things up to put the debate more on-point: Yes, our engine is "internally balanced", and that has virtually nothing to do with the debate about the pulleys.

An externally balanced engine means there's actually an asymmetrical counterweight system on the pulley, which balances against the otherwise-imbalanced crankshaft. You will definitely destroy an engine if you were to slap a random symmetrical pulley onto such an engine. Because our engine is internally balanced, there's no specific need for a balancing component on the pulley. The pulley itself is expected to have neutral balance (even weight distribution).

Even with an internally-balanced design like ours, the stock pulley includes a (neutrally-balanced) dampening ring to reduce vibrations. The debate is about whether replacing the stock pulley (poorly machined, crappy metal, with a dampener) with an aftermarket one (much lighter, machined to better tolerances, no dampener) is going to cause long term damage due to increased vibration.

On the "stock" side of the debate is the idea that the stock dampener serves to quiet important harmonic vibrations at specific RPMs, and that without it the engine will slowly tear itself apart (slowly wear out crankshaft bearings at the very least). On the "aftermarket" side of the debate is the idea that the (a) whatever vibrations the stock pulley dampens are relatively trivial and mostly about reducing engine noise heard by the user, and won't cause engine damage, and (b) the more-precisely machined aftermarket pulley is better-balanced to begin with.

There's little doubt that as you push an engine further beyond its design boundaries, you need to be more precise about balance and vibrational issues in general. The tricky question is whether our engine in basically-stock form needs that NVH ring for long-term health or not.

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