Chilean Mining Diesel Equipment Shows Strong Vibration Within a Narrow Engine-Speed Range Despite Balanced Injector Contribution as Viscous Torsional-Damper Condition Is Investigated

The Vibration Appeared Only in a Narrow RPM Band

Mining diesel equipment operating in Chile developed a strong vibration that became noticeable only within a particular engine-speed region.

Below that range, the engine ran relatively smoothly. Above it, the vibration reduced again.

Injector contribution data and basic cylinder checks did not show a clear fueling imbalance.

Engine mounts were also inspected without identifying sufficient deterioration to explain the symptom.

This speed-dependent pattern shifted attention toward the crankshaft torsional damper.

Diesel Crankshafts Experience Torsional Oscillation

Combustion does not apply torque to a crankshaft continuously.

Each firing event produces a pulse that can twist the crankshaft slightly before the shaft elastically returns.

The simplified chain is:

Combustion torque pulse → Crankshaft torsional movement → Damper absorbs part of oscillation → Remaining vibration controlled

On engines using a viscous torsional damper, internal damping characteristics are designed for the engine’s torsional behavior.

If that damping capability deteriorates, vibration can become stronger around certain resonant speed ranges.

The Narrow RPM Window Was the Main Diagnostic Clue

Injector-related roughness often follows cylinder load or remains present across a broader operating range.

This case behaved differently:

• vibration increased as RPM approached a specific range;
• peaked within that range;
• and reduced again as RPM moved away from it.

That pattern is consistent with a resonance-related investigation rather than a simple cylinder contribution problem.

Damper Condition Requires More Than an External Look

Depending on damper design, technicians may inspect:

• housing condition;
• fluid leakage;
• deformation;
• mounting integrity;
• heat exposure;
• age or service history;
• and manufacturer-defined inspection criteria.

A viscous damper can appear externally intact while its internal damping capability has deteriorated.

For that reason, service limits should follow the applicable engine documentation.

Chilean Mining Duty Made Resonance More Noticeable

Mining equipment frequently moves between:

• low-speed maneuvering;
• working RPM;
• high-load pulling;
• and deceleration.

Repeated movement through the same speed band made the vibration easy to reproduce.

That repeatability helped separate the symptom from random combustion roughness.

Why Injector Replacement Would Miss the Fault

Balanced injector contribution suggested that the torque pulses themselves were not severely unequal.

The problem was how the rotating assembly handled those pulses.

The diagnostic distinction became:

abnormal torque generation

versus

normal torque pulses with inadequate torsional damping.

Technical Lesson

A diesel engine can vibrate strongly even when combustion is relatively balanced.

When vibration peaks in a narrow RPM band and falls outside that range, technicians should consider resonance and torsional-control components rather than focusing only on injectors or engine mounts.

FAQ

Can a crankshaft torsional damper fail without obvious external damage?

Yes. Some damper faults involve internal damping degradation.

Is this the same as a harmonic-balancer timing-mark problem?

No. Timing-mark slippage affects the reference position; torsional-damper deterioration affects vibration control.