One and it's integral to the engine.
This Explorer could have either the standard configuration 4.0 cam in block or the 4.0 SOHC engine. If it is SOHC there are 4 timing chains and some of this hardware is located on the back of the engine. It is necessary to remove the engine to replace all the timing chains on a 4.0 SOHC Ford engine. The standard OHV 4.0 has 1 timing chain accessible from the front. Do some reading here on the differences...http://www.therangerstation.com/tech_library/4_0_P age.shtml
If you have the SOHC engine here is a good overview of what is required to replace the timing hardware....http://www.explorerforum.com/forums/index.php? threads/sohc-v6-timing-chain-parts-removal-procedure.316471/
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