Ok, your mechanics are telling you many things that are
not true. First, the Fiero 2.8 does not have a camshaft
chain tensioner. What it does have is a dampener that the
chain can rub against to prevent standing waves from
occurring in the chain as it goes around the sprockets.

Here is a picture:
http://web2.airmail.net/jsavage1/formula/timingchain.jpg
The dampener is the piece between the sprockets, it is made of
sheet metal with rubber coatings on each side where the chain rubs. The
chain does not have enough slack in it to allow it to jump teeth unless
the chain and sprockets are both extremely worn out, this only happens
on
engines with very high mileage or that have not had their oil changed
regularly. It is routine for pieces of the dampener rubber to wear away
and break off, no harm occurs because of this.

Now, as to the valves hitting the pistons, as far as I can tell the 2.8
engine design does not open the valves to interfere with the pistons, so
it is extremely unlikely that this happened in your case. Installing a
new
timing chain and gear set (they only come in sets) and replacing the
dampener
should fully restore your engine. Setting the cam and ignition timing is
very,
very easy in the 2.8. Since you have to remove the water pump to get to
the
timing gears I would consider replacing that as a preventative measure,
it is
very easy to clean the water pump mounting surface out of the car, which
it
has to be since it is part of the timing cover that has to be removed to
change
the timing chain set.

JazzMan