New to me '85 model. On start up after the car has been sitting for a couple days and yesterday after changing the oil, get a very loud noise from right valve cover that lasts maybe 2 seconds. My guess is it takes a couple seconds to pump the lifters up. Is this a common problem? Should I be concerned? Is there a check valve or something that needs to be fixed? At idle the oil pressure drops to 1 bar which should be normal, but seems to fluctuate much more than on my 300SE. Engine has 166K, from the amount of crud I cleaned out of the bottom of the oil filter bowl, not sure how dilegent the previous owners have been with regular oil changes etc.

You may have cam chain stretch. You should take off the valve covers and rotate engine until you can see the cam timing marks and see if there is a 'stretched' difference from one cam to the other. On the other hand, if you know it has been a long while, or if you don't know when the chain was last replaced, just go ahead and roll in another one and put in a new chein. Not really a big deal and is peace of mind in the long run. It will get rid of that clatter on the first 2-3 seconds of start up. I just converted my single chain to a double chain in my garage at home. It cured the clatter and I have peace of mind. ;) Of course, I think you have the double chain already, you just need to roll one in.

Additional Info
 

The car has the double chain. It was replaced about 40K ago by a reputable shop. I don't have any manuals yet. Is there a tensioner and is it adjustable. Where are the timing marks. Thanks for the help.

You can buy a Haynes manual that covers model years of SL's up through 1980. The information is good for most questions and features of later models. The manual is cheap and you can find them at most any discount auto parts place. Hope this helps.

Follow up.
 

As I mentioned in the original post, the oil was pretty nasty when I changed it. Had a 3 hour trip in the car after the oil change. It has been over a week now, numerous starts, some after sitting a couple days. No noise :) My guess is the tensioner was gunked up, seems to be working now. Next time I get in stop and go will see if the oil pressure responds any differently. Planning on changing the oil at about 2000 miles. Hopefully that will get somemore crud out.

The cam tensioner has a spring tension to hold until the oil pumps up. There should be NO noise before Nor after oil pressure builds. You do have a problem. Check it out before you jump sprocket and bend valves.