Engine balancing

[Luce]

Let me take a stab at this....

A crank is sort of like the crystal wine glass the fat lady sings to and makes it break. If you tap the rim, it rings. If you sing the exact same frequency to it, in the right location, the pressure waves will reinforce the vibrations causing the ring, and the vibration will increase until the forces are stronger than the glass, and it breaks. If you keep a finger lightly touching the rim, the vibrations are dampened and absorbed, and can never reach a dangerous level.

The soft mounted weigh of the harmonic dampener is that lightly touching finger. It dampens high frequency vibration that the pistons and rods can induce. A good crank will ring too if smacked, but not anywhere near as long if the harmonic balancer is installed.

And another reason the clutch disc doesn't need to be balanced WITH the rest of the rotating mass is because it's not indexed. Each time the clutch is engaged, it stops at a different place.

[AL427SBF]

Originally Posted by Luce

Let me take a stab at this....

A crank is sort of like the crystal wine glass the fat lady sings to and makes it break. If you tap the rim, it rings. If you sing the exact same frequency to it, in the right location, the pressure waves will reinforce the vibrations causing the ring, and the vibration will increase until the forces are stronger than the glass, and it breaks. If you keep a finger lightly touching the rim, the vibrations are dampened and absorbed, and can never reach a dangerous level.

The soft mounted weigh of the harmonic dampener is that lightly touching finger. It dampens high frequency vibration that the pistons and rods can induce. A good crank will ring too if smacked, but not anywhere near as long if the harmonic balancer is installed.

And another reason the clutch disc doesn't need to be balanced WITH the rest of the rotating mass is because it's not indexed. Each time the clutch is engaged, it stops at a different place.

... or just say you need to dampen the engine's resonant frequency so you don't end up like that bridge caught in the wind oscillating at its' resonant frequency until it disintegrated.
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[Bill Hughes]

I believe that I comprehend the concept of an externially balanced system. What I don't understand is, what radius is this 28 or 50 OZ external weight at each end of the crank supposed to be at?

[xb-60]

Originally Posted by AL427SBF

... or just say you need to dampen the engine's resonant frequency so you don't end up like that bridge caught in the wind oscillating at its' resonant frequency until it disintegrated.
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You're talking the Tacoma Narrows Bridge? I was just thinking about that one, after Luce's reply

[xb-60]

Originally Posted by Luce

Let me take a stab at this....

A crank is sort of like the crystal wine glass the fat lady sings to and makes it break. If you tap the rim, it rings. If you sing the exact same frequency to it, in the right location, the pressure waves will reinforce the vibrations causing the ring, and the vibration will increase until the forces are stronger than the glass, and it breaks. If you keep a finger lightly touching the rim, the vibrations are dampened and absorbed, and can never reach a dangerous level.

The soft mounted weigh of the harmonic dampener is that lightly touching finger. It dampens high frequency vibration that the pistons and rods can induce. A good crank will ring too if smacked, but not anywhere near as long if the harmonic balancer is installed.

Thanks Luce. That's making sense.