Have a 27 mm crankshaft pulley bolt that is resisting removal. Initially used a 1/2" air impact wrench with a max torque of 420 lb-ft; switched to a 3/4" impact, with a max torque of 700. Using a 6" extension bar with both to gain access to the bolt.

Unable to budge the bolt at this point. Any suggestions? Move up to a 1" drive? TIA.

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.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I've heard of that trick before (using a bar against the floor and tapping the starter). I would never do it myself. I just don't like the idea of:
1) somehow doing something dumb and spinning it in the wrong direction - imagine that breaker bar flying into the radiator and front engine accessories.
2) subjecting the crank to a torsional load along its entire length that it wasn't designed for.
3) breaking a tooth on the ring gear, warping the flexplate - who knows what else.

I have a bunch of 1/8 x 4" steel plate that is 6 or 8 feet long. Every time I need to take off one of these stubborn crank bolts I build a tool to hold the crank in place. The hub of the front pully has bolt holes to mount a puller. Just build a tool that bolts to these holes, cut a hole in the middle for your socket and then use a big breaker bar with a cheater bar (pipe) to get it loose.

I personally would rather use this approach than crossing my fingers, hitting the key and hoping that I don't have a bunch of broken parts a split second later.

I don't use an impact driver on those bolts because booger-ing up threads in the crank snout would be terrible.

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.