I took the valve cover off my 1980 300SD, 220k miles, to adjust the valves and check the timing chain before a cross country trip. I found the timing chain to be loose. There was about 1/2 mm clearance between the tensioning rod and the chain rail.
I checked the cam timing by lining up the cam timing marks and reading the timing marks on the damper and it was only off by 2 degrees.

I think that this means that there is a problem with the chain tensioner and not a worn (stretched) timing chain. I think the tensioner works on oil preassure and a spring
My other 300SD was off by 3 degrees, but the chain was tight because there was no clearance as above.

Am I right about the tensioner? If so, what has to be replaced in the chain tensioner? Can the offset keys be put into the camshaft and gear without separating the chain?

Thank you for any advice.

Paul

You are partially correct. The loosness is because of the lack of oil pressure and where the cam is sitting and is very normal. If you have no more than 3 degrees, let it go. At or beyond 3, you will need to replace the timing chain, sprocket and tensione...Only with factory or OE manufacturer parts.

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