Basic provisions
1. The timing gear is an integral part of the camshaft bearing caps. The cams are mounted on separate short shafts that are seated in the camshaft bearing caps. Each cap has one exhaust cam and one intake cam.
2. Hydraulic tappets are mounted on the cams and are supplied with oil through holes in the cams.
Removal
3. Remove the air cleaner as described in Chapter 4.
4. Remove the camshaft cover as described in paragraph 4.
5. Remove the camshaft sprocket as described in paragraph 8.
6. On models with adjustable valve timing clearances, loosen the locknuts and turn the cam adjusting screws out as far as possible.
7. Check for identification marks on the cams and bearing caps. Caps are usually numbered 1 through 4, counting from the sprocket side of the exhaust manifold side of the bearing caps (see fig. 10.7). The corresponding mark is cast on the cylinder head under the camshaft. If any of the covers is not numbered, apply the corresponding marks using a punch.
Fig. 10.7. Identification mark of the camshaft bearing cap (shown by arrow)
8. Gradually, working in a diagonal sequence, unscrew the camshaft bearing cap bolts. Remember the location of the oil splash tube brackets.
9. Lift up the oil spray tube (see fig. 10.9).
Fig. 10.9. Raise the oil spray tube
10. Remove the bearing cap/cam assemblies (see fig. 10.10). Note that the lids are installed on pins - if they are stuck, lightly tap the lids with a mallet.
Fig. 10.10. Removing the bearing cap/cam assemblies
11. On models with hydraulic valve lifters, remove the valve lifter contact pads from the valve stems, keeping them in strict order (see fig. 10.11). You cannot swap parts.
Fig. 10.11. Remove the valve tappet contact pads
12. Carefully remove the shaft from the cylinder head.
On models with hydraulic valve lifters, store the contact pads in a divided box with eight compartments labeled 1 through 4 for intake valves and 1 through 4 for exhaust valves.
Disassembly, inspection and assembly
Camshaft
13. Check the bearings and camshaft lobes for signs of wear, scoring, deep scratches or pitting. If any are found, the shaft must be replaced. Any damage of this nature indicates a blocked lubrication channel either in the cylinder head, or in the cam assembly, or in the oil splash tube. To determine the cause, you need to carefully inspect the parts. When replacing the camshaft, the cams are also replaced at the same time.
Cam drive gear
14. With the camshaft bearing caps removed, the cams can be removed from the caps by pulling out the short cam shafts. Before removing the cams, check for identification marks and, if any are missing, apply them (designate cams 1 through 4 for intake valves and 1 through 4 for exhaust valves). Do not swap parts. Pay attention to how the cams are installed on the shafts.
15. To remove the cam shafts, it is best to use a proprietary device consisting of a sliding hammer and a special adapter. An alternative method is to screw a suitable long bolt (M8) with a washer into the cam shaft, then to pull the shaft out, you need to hit the washer with a hammer. Be careful not to damage the parts (see fig. 10.15). On the removed shaft, the cam can be removed. The parts must be stored in strict order, for example in a box divided into compartments.
Fig. 10.15. Using the M8 bolt to pull the cam shaft out of the bearing cap
16. On models with adjustable valve clearances, check the wear of the adjuster tips that contact the valve stems. Check how the cams are installed on their shafts. If visible wear or damage is found, replace the parts as a set.
17. On models with hydraulic tappets, check the wear of the tappet contact pads. Check how the cams are installed on their shafts. If visible wear or damage is detected, it is recommended to replace the parts as a set.
18. Clean the parts thoroughly before installation.
19. Lubricate the mating surfaces of the cams and shaft, then, observing the notes below, install the shaft and cam on the appropriate bearing cover.
- a) If working parts are being installed, make sure that they are installed in their original locations.
- b) Ensure that each tappet is installed correctly on the shaft as noted prior to removal.
- c) Make sure that the groove for the camshaft bearing cap mounting bolt on each shaft is aligned with the bolt hole in the cap.
- d) If you do not have the original tool for installing the camshaft into the cover, use the long bolt and washer that you used when removing it.
Hydraulic valve lifters
20. To remove the tappet from the cam, insert a suitable drift into the hole in the top of the cam and push the tappet out of the cam.
21. Remove the adjusting washer from the tappet housing in the cam (see fig. 10.21).
Fig. 10.21. Valve tappet/cam assembly
1 Cam
2 Adjusting washer
3 Valve tappet
4 Contact pad
22. Keep the valve lifters and washers in proper order so that they can be installed in their proper places.
23. Check the valve tappets and washers for wear. If any wear or damage is found, replace them.
24. The design of hydraulic tappets is such that the amount of play or clearance that they can compensate for is limited. This is mainly determined by the small size of the units. To maintain the clearance at a minimum level and to ensure that the tappets can operate within their operating limits, adjusting washers of varying thickness are installed.
25. Under normal conditions, the tappets automatically adjust to provide the required clearance between the cam and the valve stem.
26. However, if the parts are significantly worn or after replacing the camshaft, cams, valves or tappets themselves, the valve assembly becomes noisy in operation, perhaps the clearances have gone beyond the automatic compensation. In this case, it is necessary to replace the adjusting washer with a different size.
27. To determine the required thickness of the adjusting washer, a special indicator device and a clamp are required. The work should be entrusted to a Mercedes-Benz dealer.
28. It is recommended that the valve lifters be installed with the cams already installed on the cam shafts. This will reduce the time required for installation and reduce the possibility of oil draining from the valve lifters if they are prepared as described below.
29. Before installation, each valve must be filled with oil. To do this, hold the assembly vertically and fill the chamber with clean motor oil. Using a piece of thin wire inserted through the chamber, press on the ball valve to allow oil to flow into the working chamber (see fig. 10.29). At the same time, press the pusher up to the limiter. Repeat these steps several times until the oil stops flowing into the working chamber.
Fig. 10.29. Press the pusher ball valve with a piece of thin wire
30. Install the adjusting washer onto the cam body with the oil recesses facing the tappet, then insert the tappet. Push the tappet down until it contacts the retaining ring. The bearing cap/cam assembly can now be installed onto the engine.
Installation
31. Lubricate the camshaft and bearings in the bearing caps and cylinder head with clean engine oil, then place the camshaft in its place on the cylinder head. Turn the camshaft so that the timing mark is aligned with the top plane of the cylinder head - see paragraph 3 (see Fig. 10.31, a. b).
Fig. 10.31, a. Lubricate the camshaft thoroughly
Fig. 10.31, b. Align the camshaft groove (shown by arrow) with the upper plane of the cylinders
32. On models with hydraulic lifters, install the lifter contact pads onto the corresponding valve stems.
33. On models with adjustable valve clearances, make sure the adjusting screws are fully out.
34. Install the bearing caps in their positions with the identification numbers facing the exhaust manifold and the mating surfaces of the oil splash tube brackets facing rearward.
35. Position the oil supply tube on top of the bearing caps, making sure the oil holes in the tube are aligned with the corresponding holes in the bearing caps.
36. On models with adjustable clearances, install the cover bolts and tighten them gradually, in a diagonal sequence, to the torque required by the specifications.
37. On models with hydraulic valve lifters, perform the following steps:
- a) Turn the camshaft so that the cams of the first cylinder shaft are facing down, i.e. away from the cam - so that the pusher is without load when tightening the cover bolt.
- b) Install the 1st bearing cover bolts and gradually tighten the bolts to the required torque.
- c) Repeat steps a) and b) for bearing cap No.3, No.4 and finally No.2, turning the camshaft so that the corresponding cams are facing downwards when tightening the bolts.
38. If this has not already been done, rotate the camshaft so that the timing mark is aligned with the top plane of the cylinder head. Then check that the crankshaft timing mark is aligned with the TDC position of cylinder 1 (see paragraph 3).
39. Install the camshaft sprocket as described in paragraph 8.
40. On models with adjustable valves, adjust the clearances as described in Chapter 1A.
41. Install the camshaft cover as described in paragraph 4.
42. Install the air cleaner.