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SymptomsTSBs detail noise as loud ticking heard specifically from the top-left of the engine (rear V6 bank, near cylinder #1) and oscillatory in frequency over ~3 seconds (beats). The noise is most noticeable on cold-starts and
stops past 2k-rpm thus differentiating it from carbon-knock or HLA noise.
CauseThe exhaust-cam friction-gear-spring is designed to prevent backlash through the helical cut gear at low rpm.
At higher rpm (>2k) backlash isn´t a problem and it isn´t required, the noise stops. The problem is that the friction-gear can only eliminate backlash over a certain range - excessive HLA lash (dirty oil/HLAs), hunting idle or slight miss-fire will alter the backlash through the cam sufficiently to move it outside the ability of the friction gear to compensate, thus it becomes audible. The noise is simply annoying, the device being fitted for aesthetics and not a critical wear issue.
SolutionThe only solution is a new friction-gear for the exhaust-cam, it can be done without doing the timing belt, but if it is done at a Main Dealer it may be beneficial to do the timing belt simultaneously regarding cost. The task is over 7hrs labour, with the friction gear itself just US$12 or Ł12. Friction Gear noise is often HLA noise, and is not a problem requiring remedy - it´s purpose is aesthetic to achieve a totally silent V6 engine.
T.
Ford Probe 2.5 GT ´93, Praha