Hi Chris, the 104 engines have had very few timing chain problems. It's easy enough to check to see if it's stretched. Removing the valve cover is all you need to do, and you can check it periodically, for instance when you're replacing spark plugs and you've got it halfway apart already. The 116/117 engines, and to a lesser extent the 603 diesel are notorious for their chain problems, but not the 104. If you're determined to replace the chain anyway, simply roll in a new one when the cylinder head is off during head gasket replacement! Good luck