Removal the cylinder head
If the engine has not yet been removed from the vehicle, first perform the following operations:
1. Disconnect the ground wire from the battery.
2. Remove the intake and exhaust manifolds.
3. Remove the air conditioning compressor, where applicable.
4. Remove the ignition distributor, high tension wires and spark plugs.
5. Remove the rear suspension automatic level control hydraulic pump, where applicable.
6. Disconnect all wires and hoses and drain the cooling system.
7. Remove the oil level indicator dipstick tube, where present.
Engine M123
Removing the camshaft gear
Tightening sequence of cylinder head bolts on M 123 engine
The arrows indicate the small cylinder head bolts in the timing chain opening (engine M 123)
1. Loosen the nuts and remove the valve cover.
2. Loosen the clamps and remove the bypass hose between the water pump and the thermostat housing. Remove the thermostat housing.
3. On vehicles with automatic transmission, remove the strut between the right engine mount and the cylinder head.
4. Turn the crankshaft pulley bolt until both valves in cylinder 1 are closed and the TDC mark on the vibration damper is aligned with the ignition timing arrow.
5. Make marks of the relative positions of the chain and camshaft sprocket.
6. Unscrew the chain tensioner plug and remove the spring. Then unscrew the nuts and remove the tensioner body together with the plunger.
7. Loosen the camshaft sprocket bolt, locking the sprockets using a metal rod inserted into one of the holes.
8. Move the sprocket aside, remove it from the chain and tie it to one side. Note that the marks on the sprocket are on its outer face.
9. Loosen the bolts and remove the ventilation tube running from the water pump to the cylinder head.
10. Remove the cylinder head bolts in the reverse order to that shown in the illustration using an Allen key. Don't forget the two bolts in the camshaft tunnel. Note that the longer bolts are on the camshaft supports.
11. Have an assistant lift the chain and hold the chain guide inside while you remove the cylinder head from the block. If it is stubborn, tap it with a wooden mallet. Do not insert a lever into the gasket slot to avoid damaging the mating surfaces. Place the cylinder head on wooden blocks to avoid damaging the valves.
12. Remove the cylinder head gasket from the block.
Engine M110
Removing the valve tappet (engine M 110)
TDC marks on the camshaft gear and its housing (engine M 110)
Removing the side guide studs (engine M 110)
Tightening sequence of cylinder head bolts on M 110 engine
1. Remove the vacuum pump (where provided by design).
2. Using Allen keys, loosen the bolts and remove the front camshaft covers.
3. Loosen the oil return pipe bolts.
4. Loosen the clamps and remove the bypass hose from the water pump to the thermostat housing. Remove the housing.
5. Unscrew the nuts and remove the valve cover.
6. Separate the springs from the cam followers using a screwdriver.
7. Rotate the crankshaft pulley bolt until the tops of the cam lobes in cylinder 1 are at the top position, then lower the valve levers to remove the cam followers. Mark the positions of the followers. Repeat this operation on the remaining valves.
8. Rotate the crankshaft pulley bolt until the cam lobe peaks in cylinder 1 are at the top position and the TDC mark on the vibration damper is aligned with the valve timing indicator. Make sure that the marks on the camshaft sprocket are aligned with the marks on its housing.
9. Unscrew the camshaft sprocket bolts, blocking the sprockets with a metal rod passed through one of the holes.
10. Remove the radiator. This operation is desirable, as it will free up space for work.
11. Using a hexagonal socket wrench, unscrew the chain tensioner plug and loosen the inner plug approximately two turns. Unscrew the outer ring and remove the tensioner. If it sticks, unscrew the inner plug and screw in the bolt to remove the unit.
12. Use a hammer to knock out the pins and remove the upper guide rod from the camshaft housing.
13. Move the camshafts all the way back, remove the spacers and chain from the sprockets and tie the chain to one side.
14. Unscrew the cover plug, take out the support pin and remove the chain guide sprocket.
15. Use a hammer to knock out the pins and remove the side guide rod from the cylinder head.
16. Loosen the cylinder head mounting bolts in the reverse order to that shown in the figure, using an Allen key. Don't forget the two bolts in the chain opening.
17. Have an assistant lift the chain and hold the right chain guide inside, then remove the cylinder head from the block. If it is sticking, tap it with a wooden mallet to loosen it. Do not insert levers into the gasket slot to avoid damaging the mating surfaces. Place the cylinder head on wooden blocks to avoid damaging the valves.
18. Remove the cylinder head gasket from the block.