I had the timingchain changed on my '86 300E just for the peace of mind. I asked the mechanic for the old one to compare it with the new one. The difference was about 1/2 inch in length. The milage is about 250K on the car. It cost me $300.00 canadian including the tennsioner (aftermarket), chain and the drivebelt (both original Merc.). It may not have been necessary but I sleep better now, what can I tell you.