I am no expert, but I think that the majority, if not all of the first and second generation Explorers use Timing Chains, and not belts. The likelihood that the chain will fail leading to catastrophic engine damage is very small. There is no regular maintenance requirement for the chain in the '92 Exp (which I have). However, there have been problems with the timing chains. In the 1998 4.0 SOHC engine, there is a technical service bulletin out on the subject. Here is a link to it
http://www.alldata.com/TSB/20/982015D1.html

You can do a search on this site for timing chains to get more data.
Also, look over at: https://www.ford-trucks.com/ and do a search as well.

Regards,
John