Well about 3 yrs. ago when I got the 85 300 SD a mechanic told me I should replace the timing chain because when he adjusted the valves he could see the chain tensioner was near the end of its adjustment to keep tension on the chain.I did some research on chain replacement and no place did it mention by looking at the tensioner that would dictate chain replacement every where said to measure stretch by either of 2 ways 1st lining up marks on cam tower I got 0 or 1 degree. The more precise way to measure by taking lash out of 1 intake valve then measureing the reading when the valve drops 2 mm or .078 which I did and again came up same reading 11 right on or 12 degrees . All the rails looked good the spring in the tensioner did show some wear and was about 1/4" shorter then the new one so I did replace that but think I am not going to replace chain as I do not see how I can better the readings I got. Looking from top of engine down the adjuster is sticking out about 1/4" against the tensioner rail. The car has about 300,000 on it but dont know the history on it. Like to hear some thoughts on matter. Oh and I really do'nt know why you would have to pull whole tensioner out when all you have to do is take center bolt out to take spring out and release tension when rolling a new chain in?