If you look at the cam sprocket and compare it with the crank sprocket, you'll see that the cam is driven at 1/2 the speed of the crank. This has to be as when #1 is on power stroke, the valves stay closed until just before BDC, then the exhaust begins to open and stays open until just before TDC on the exhaust stroke. Same with the intake. Closed at TDC on the power stroke, stays closed until just before TDC on exhaust stroke. If the cam were turning at 2x crank speed, each valve would be opening twice on each power and exhaust cycle. Each valve has to be open only once in 720 degrees of crank rotation. What you have to be sure about is which TDC your looking at when you do the final setup of the timing chain. Basically three things have to be in synch. #1 is at TDC on compression stroke, the cam is aligned so both valves are closed at that point. You can usually feel some slight play at the end of the valve lifter. You can also see if the cam followers are on the flats of the cam base circle. And, the rotor is sitting at the firing position for number one cylinder on the distributor cap. Another tip is if you look at the engine from the front, it rotates clockwise. If #1 cylinder is at TDC on compression, check the position of the cam lobe on the exhaust valve, it should be approximately 180 degrees away from the cam follower because that valve doesn't open until the crank has traveled all the way thru the power stroke and is beginning the exhaust stroke, i.e. heading back towards TDC. Hope this helps. Remember 3 things need to be in harmony, the cam, the crank and the ignition. With this done, you will have good Karma and your Benz will love you. Many folks get flustered with all the hoopla about this procedure. If you sit down and think about it, it's not too hard to figure out. Happy motoring..
1987 BMW 325