hello and welcome to the site cheers..
the engine timing chain is known to fail on earlier engines and I would recommend you get it changed.
cost will be about £350 ish, so similar to a cambelt change.
once changed it will last 100,000 miles, so worth doing as a new engine costs £1500 :shock:
the engine was designed by General Motors
the blocks don't crack, but the heads can crack if the spark plugs are over tightened :roll:
plenty of info on the site, so enjoy 😃