Not normal. The tensioner has a check valve to keep the chain tight. I would replace it before starting the car again. With the new piece installed, pull the green wire out of the ignition unit and crank the engine until you get oil pressure. Then plug it back in and start the car.

This is a common failure. Tensioner bleeds down while sitting, engine starts before it's pressurized, chain jumps.

In fact, this may already have happened. Can you check the cam marks against the timing marks, since you have the covers off?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe