Manually Turn Mercedes-Benz Engine Crankshaft

This guide provides instructions on manually rotating (turning over) the crankshaft on Mercedes-Benz engines.

What you will need

To manually crank a Mercedes-Benz engine, you will need the following tools:

• 27mm socket
• Ratchet Wrench

Procedure

1. Park your Mercedes-Benz and set the parking brake.
2. Allow the engine to cool down.
3. Switch the ignition off, keep the key away from the car so nobody can start it, and pull the hood release under the dashboard.
4. Remove the front part of the engine cover by lifting it.
5. Locate the crankshaft pulley at the front of the engine.
6. Place the 27mm socket on the bolt at the center of the crankshaft pulley (27mm fits most Mercedes engines; check yours).
7. Rotate the ratchet clockwise.

Do not rotate the engine counterclockwise.

Turning it backwards can let the timing chain jump a tooth or loosen the crankshaft bolt. You will need to apply a considerable amount of force. V8 and V6 engines are harder to turn over than 4-cylinder engines.

Also, as the various cylinders reach the Top Dead Center (TDC), turning the crankshaft will get harder then easier once past the TDC.

If you have difficulty turning over the engine, remove the drive / serpentine belt and try again. Remove the spark plugs if it is still difficult to crank your Mercedes-Benz engine manually.

If your crankshaft doesn’t turn, you will likely have a mechanical problem, such as a broken timing chain, bent valves, bad bearings, etc.

Mercedes-Benz Engine Won’t Turn Over.

Typical problems that can prevent a car from turning over include.

• Seized starter
• Damaged crankshaft bearings
• Engine hydro locked.
• Engine sized
• Timing chain problem
• Bent valves

This is often necessary if your Mercedes does not start and you want to verify that the engine is not seized or locked up.

This procedure is also required for several maintenance procedures, including changing the timing chain, checking for timing chain wear, time injection pump, camshaft replacement, etc. If your engine will not turn over, in most cases, it is due to mechanical problems.

When You Need to Turn the Engine by Hand

• Lining up timing marks during timing chain or camshaft work
• Reaching the torque converter bolts through the inspection hole
• Checking that the engine turns freely after a repair, before you start it
• Checking for a hydrolocked or seized engine

If the Engine Will Not Turn

Do not force it with a longer bar. An engine that suddenly stops turning may have liquid in a cylinder, a jumped timing chain or valve contact. Remove the spark plugs to release compression and check for fluid; if it still will not turn, find the cause before going further.

Frequently Asked Questions

Why must I turn a Mercedes crankshaft clockwise only?

Turning it backward can let the timing chain go slack on the tensioner side and jump a tooth, which can bend valves. Clockwise, viewed from the front, is the normal running direction.

What size socket fits the Mercedes crankshaft bolt?

A 27mm socket fits most Mercedes engines, as listed above. Check yours before buying, since some engines differ.

Can I turn the engine by bumping the starter?

Not for precise work. The starter moves the engine too far and too fast to line up marks, and it is unsafe with tools near the belts.

Check these troubleshooting and repair guides for more help on your Mercedes-Benz.

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