TEC-1,
I'm sorry to hear about your problem. A couple of questions: If the tensioners were replaced and the problem wasn't resolved, it would seem that Ford should continue working to fix the problem if the tensioners failed again. The repair itself is warrantied unrelated to the original problem. If you mentioned it to your dealer what did he say? Since the replacement tensioners have failed, why is Ford wanting to replace the entire engine? Damage to what other engine parts based on tensioner failure? How many miles on your vehicle when the problem started? Miles before you went to Ford complaining? Has Ford given you any reason why they won't cover the fix besides being out of warranty?
BTW, the warranty isn't an ironclad answer to everything. It is just one of the terms of your purchase agreement with Ford. Lawsuits on negligence theories can be, and are won, long after the warranty has expired. Ford, and every other manufacturer of any product, would be very happy if you thought you had no recourse once the warranty expired. If the product fails because it was a faulty product design that caused/contributed to the failure, you very well might win. If the tensioners failed because they were assembled incorrectly you also stand a good chance of winning on a negligent manufacturing defect theory.
The bottom line is don't let Ford refuse service based on the warranty especially where other owners are reporting identical problems. If yours was a single and isolated incident the odds would be greater against you but that doesn't seem to be what is happening here. If you don't get any satisfaction from them you might want to talk to a products liability attorney first and depending on their answer, consider a small claims suit. Please keep us posted.