Needs timing belt How hard to replace - 1997 Pontiac Sunfire

belt hard and needs replacing
belt loose and needs adjsuting
some thing with a bearing is failing and becoming hard to spin

Most LIKELY is either the belt needs to be replaced or the belt tensioner needs to be replaced. The belt gets hard and "slick" as it ages, the tensioner holds the belt tightly against the pulleys. Either could cause slippage (hence the squeal) when the A/C comes on.

Trick question. The 2.7L has a timing chain and not belt. 3.0L needs a new belt every 60,000 but some companies sell a kevlar/nitrile replacement that's supposed to be good for 100K. Do the water pump at the same time. 2.4L needs a belt at 60K.

check the timing belt it might have jumped a tooth throwing the timing off this is a sign before the belt blows then the valves bend

The timing belt should have been replaced at the 105K service. Someone should look at the timing belt to determine the condition. However, if you have any doubts, you should replace it to be on the safe side. Also replace the mechanical tensioner.

I believe by 2000 interference motors are no longer, but anytime you drop a timing belt when the engine is running at 2,500 RPM's that is hard on the valve train.
I would replace the belt and try it out.
Let me know if you need the procedure, and how it goes.

Technically, nothing else needs to be changed when replacing a timing belt, however it is recommended or suggested to replace the timing belt tensioner and water pump while doing the belt. These items are only accessable when doing a timing belt. The cost should be under $100.00

needs to be replaced every 100,000 Miles

sounds about right. timimg belts are not replaced that frequently. I have a truck with over 80,000 miles, and haven't replaced the belt yet.

It's in it's own casing, screwed to the block, just above the alternator, under the intake manifold.

Check previous posts regarding new fitting timing belt Although a different capacity motor, this should help you:

here