Timing chain replacement is generally determined by the amount of stretch. If your chain is original then I would imagine it is overdue for replacement...general consensus seems to be around 200k until the stretch becomes worrisome.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth