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Crankshaft pulley rubber perishes

The crankshaft pulley on this engine is two metal rings bonded together through a rubber layer that damps torsional vibration. That rubber perishes with age rather than with distance, which is why the one source that documents this for the fourth generation says the failures turn up on trucks of a certain age regardless of how far they have gone. One source is why this entry carries the site's weakest confidence tier: the Spanish-language owner record beside it covers earlier trucks, and its single fourth-generation entry is somebody asking for a torque figure rather than reporting a failure — and every fourth-generation truck is now that age. When the bond lets go, the outer ring walks relative to the hub: the belt runs off line and squeals, then throws, and everything the belt drives stops. Spanish-language owner reports on the same family of trucks describe the related failure of the centre bolt working loose or breaking, which the first-generation entry on this site documents in detail from federal complaint records. Treat a wobbling pulley the same way in both cases: stop. Losing the belt takes the water pump and the steering assist with it, which is why this is filed as safety-critical work for a qualified mechanic rather than a noise to monitor.

Gen 42006–2021CR · UK · AU · JDM · EU · ME · GLOBALDamages other partsAnecdotalSafety-critical

Do not driveNo lo maneje

Safety notice — Engine.

This affects a safety-critical system. Reference material only: for safety-critical work, consult a qualified mechanic.

Esto afecta un sistema crítico para la seguridad. Material de referencia únicamente: en trabajos críticos para la seguridad, consulte a un mecánico calificado.

Anecdotal. This entry is not backed by factory documentation — treat its values and steps as a starting point, not as if they came from the factory manual.

Anecdótico. Esta entrada no se apoya en documentación de fábrica — tome los valores y los pasos como punto de partida, no como si vinieran del manual de fábrica.

Symptoms

  • A belt squeal on a cold start that clears as things warm up
  • The pulley visibly wobbles or runs off line at idle
  • Black rubber crumbs collecting around the front of the engine or on the undertray
  • The drive belt has been thrown off or has shredded

Likely causes

  1. The rubber bonding the pulley's outer ring to its hub has perished and is letting go
  2. The pulley centre bolt has worked loose or broken
  3. The drive belt or its tensioner is worn, which makes a similar noise from a healthy pulley

Diagnostic steps

  1. With the engine stopped, shine a light on the rubber ring between the pulley's outer and inner sections and look for cracks, bulging and separationPoints toThe rubber bonding the pulley's outer ring to its hub has perished and is letting go
  2. At idle, watch the outer ring against the hub — timing marks that appear to move relative to each other mean the bond has gonePoints toThe rubber bonding the pulley's outer ring to its hub has perished and is letting go · The pulley centre bolt has worked loose or broken
  3. Look for black rubber crumbs and belt dust in the undertray and around the front of the enginePoints toThe rubber bonding the pulley's outer ring to its hub has perished and is letting go · The drive belt or its tensioner is worn, which makes a similar noise from a healthy pulley
  4. Check that the pulley centre bolt is still there and pulled down flushPoints toThe pulley centre bolt has worked loose or brokenRules outThe drive belt or its tensioner is worn, which makes a similar noise from a healthy pulley

Fix paths

Replace the crankshaft pulley

$$–$$$Difficulty 4/5

A perished pulley is replaced, not repaired. A Costa Rican counter lists this part category, which is worth knowing before somebody quotes you weeks of import lead time — though the listing is a quote request, not a stock check.

Renew the drive belt and tensioner

$–$$Difficulty 3/5

Do these with the pulley whatever else you find. A belt that has been running on a wobbling pulley has been abraded unevenly and will not last.

Renew the centre bolt to the factory torque

$–$$$Difficulty 4/5

Owner reports in the cited Spanish-language record describe this bolt loosening again after a repair on other trucks in the model line, so the torque figure and the thread condition both matter. Take the figure from the factory manual and do not accept a number quoted from memory.

Sources

  1. Mitsubishi Pajero 4x4 Life — "Pajero 3.2 DI-D common problems": lists crankshaft pulley (harmonic damper) failure on both the third and fourth generations, with cold-start squeal, visible wobble and rubber crumbs as the symptoms, notes that "rubber perishes with age rather than mileage, so failures turn up on ten to fifteen year old vehicles", and warns that ignoring it can escalate to an engine-out repairOwner forumarchived copy
  2. Opinautos — Mitsubishi Montero, reportes de dueños sobre la polea del cigüeñal: seven entries spanning 1994 to 2008 model years describing the pulley working loose, the centre bolt breaking or disappearing, and repeat failures after refitting. The single fourth-generation entry (a 2008 3.2 DI-D) is a request for the tightening torque rather than a failure report, so it evidences the question owners ask, not a fourth-generation failureOwner forumarchived copy
  3. Repuestos USA Motors, Tres Ríos, Cartago, Costa Rica — catalogue category page listing "polea principal del motor o damper"; a quote-request listing, not a per-vehicle stock or price checkVendor cataloguearchived copy