Originally Posted by DoktorT
Just way too big a chunk to ignore. More chunks will follow. Other chunks could be floating around in the chain case. Plan to pull the timing cover this winter, inspect the chain and gears, replace the tensioner rail/s and perhaps the spring.
Don't wait for nasty noises. That would likely mean much more cost than fixing this obvious flaw BEFORE any nasty noises get started.
PS - He's in Western Australia ... It's getting to be spring for him ;-)
Take the timing chain cover off NOW.