aantonic,

You got some good replies here, but they mostly apply to the diesels and other engines.

The tensioner will typically not indicate problems because of oil pressure because on the M103 it is a ratcheting tensioner. As the chain wears the tensioner ratchets tighter. When you change the chain you MUST push the ratchet plunger all the way through the mechanism and reinsert it from the outer direction to give the system slack and allow it to begin ratcheting again. If you don't do this you can break something when tightening everything up on the new chain.

The chain and associated parts are inexpensive as a previous responder indicated, but replacing it is not too bad. The tough part, until you learn the trick to it, is putting the upper timing cover back in place so that it doesn't leak. It is a chronic leak problem unless you put it in place correctly.

Once the upper timing cover is off, you merely cut a link off the old chain at the very top, temporarily connect the new chain to old and feed it through while turning the crankshaft bolt. This is done with tensioner removed. Once you have it in place, CHECK THE CAM TIMING and then peen the master link carefully in place.

The trick to putting the upper timing cover in place is using the special sealant from MB for the lower U Seal, it will let the cover slide into place without moving the U Seal out of place.

These chains are remarkably long lived given that they are a single row chain. I believe that this is due to the ratcheting tensioner.

My personal belief is that the double row chains on the diesels and in line SOHC single bank engines will last virtually forever if the oil and filter are changed FREQUENTLY. However, the single row chains are beginning to be suspect now that miles are stacking up on lots of these engines. If you look at mplefluer's picture in one of his threads, you will see chain failure picture he has very kindly posted. With nothing more than his picture to look at, I am still not sure whether his chain failure was metal fatique or wear-through. But I just ordered a new chain for my M103 engine that has 198,000 miles with 3,300 mile hot oil and filter changes. His picture and some other statements of failure have changed my theory about single row chain life. I still hold by my thinking as far as double row, single bank engines go.

Hope this is helpful and have a great day,