You'll likely get a bit more bite with a 1" vs. 6" extension.
The following may not be advised by pro MB mechanics; if so, I suspect they'll chime in. I've used the following technique successfully on more than one occasion on non-MB vehicles.
Looking at the bolt from the front, the engine rotates in a clock-wise direction. Take a sturdy breaker bar of sufficient length and attach a good 27mm socket. Attach the socket to the crank pulley bolt and turn the engine clock-wise manually until the right hand end of the breaker bar is touching the ground.
Next, disable the ignition system on your vehicle. This is EXTREMELY important.
Now get inside the vehicle and very quickly hit the starter. DO NOT try to start the vehicle. Merely "tap" the starter VERY quickly.
The engine will turn and meet the resistance of the socket/breaker bar/concrete floor.
This techinque works quite well on vehicles that have crank bolts torqued at approx. 125-150 lbs. I do not no the torque spec. on an MB 27mm crank bolt. I've "heard" that it's quite high.
1991 300-SEL - Model 126
M103 - SOHC
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