Tensioner
Note: A new tensioner cover nut O-ring will be required during installation.
Removal
1. Disconnect the negative battery terminal.
2. Raise the hood to the fully open position.
3. Working from the right side of the engine, loosen the tensioner cover nut and remove the spring and sealing ring (see fig. 8.3).
Fig. 8.3. Timing chain tensioner parts
Warning: The cap nut is pressed down by the force of the spring compression. Therefore, be prepared for it to slip off when the nut reaches the end of the thread.
4. Using a suitable Allen key or Allen key, loosen the tensioner threaded ring and remove it from the housing.
5. Remove the tensioner push rod/housing assembly from the socket.
6. Press the tensioner plunger and retaining ring out of the tensioner housing (see fig. 8.6).
Fig. 8.6. Press the tensioner plunger (1) and the retaining ring (2) out of the tensioner housing (3) in the direction of the arrow
Examination
7. Thoroughly clean the tensioner parts and check the wear of the push rod and tensioner housing.
8. Check the condition of the retaining ring and tensioner spring, and replace if necessary. If there is any doubt about the condition of the spring, replace it.
Installation
9. Insert the tensioner housing into the socket in the chain cover.
10. Screw the threaded ring into the housing and tighten it to the required torque.
11. Push the push rod together with the retaining ring into the tensioner housing until the push rod reaches the stop in the tensioner housing. Remember that the smaller end of the push rod is installed towards the tensioner rail.
12. Install the spring and new sealing ring onto the cover nut, then push the cover nut down and screw it onto the end of the tensioner housing. Be careful not to "bite" the nut.
13. Tighten the tensioner cover nut to the required torque.
14. Connect the negative battery terminal.
Camshaft Sprocket
Removal
15. Remove the upper chain cover as described in paragraph 6.
16. Turn the crankshaft so that the piston of the 1st cylinder is set to the TDC position, making sure that the valve timing marks are aligned as described in paragraph 3.
17. Remove the camshaft timing chain tensioner as described earlier in this paragraph.
18. Using quick-drying paint or a scraper, make marks on the camshaft sprocket and on the corresponding link of the drive chain. Likewise, make marks between the cake and the camshaft sprocket.
19. Unscrew the three bolts securing the camshaft sprocket.
20. Remove the sprocket from the camshaft on models with self-adjusting suspension together with the driven sleeve of the hydraulic pump), remembering the installation method and separate the sprocket from the chain. Maintain chain tension and support the chain at the top of the casing to prevent it from falling off the camshaft sprocket.
21. Remove the woodruff key from the end of the camshaft.
Examination
Note: During the production of vehicles, various modifications of camshaft sprockets were made. If a sprocket needs to be replaced, it is strongly recommended that you consult with your Mercedes-Benz dealer.
22. Check the wear on the sprocket teeth. Each tooth forms a reverse "V". If they are worn, the stress side of each tooth will be slightly concave when compared to the other side of the tooth (i.e. the teeth will look like a hook). If the teeth are worn, the sprocket should be replaced.
Installation
23. Where provided, install a woodruff key onto the end of the camshaft.
24. Ensure that the timing marks remain aligned as described in paragraph 3. If a new sprocket is to be installed, transfer the alignment mark from the old sprocket to the new one.
25. Place the chain on the sprocket, aligning the marks made before removal.
26. Place the sprocket onto the shaft, making sure it is properly installed as it was before removal.
27. Install the sprocket mounting bolts and tighten them to the required torque, holding the shaft from turning as during removal.
28. Install the chain tensioner as described earlier in this paragraph.
29. Using a suitable wrench, rotate the crankshaft at the crankshaft pulley/damper hub bolt two full turns and check that the timing marks remain aligned. If not, the chain is probably out of alignment by one tooth. In this case, remove the sprocket and reposition the chain.
30. Install the upper camshaft housing as described in paragraph 6.
Crankshaft sprocket
Note: To install the sprocket, it must be heated to approximately 50°C. Removing the sprocket in this manner requires the use of an electric portable grinder to cut the chain link. Purchase this machine and a new link before attempting this work. A puller may be required to remove the sprocket.
Removal
31. Remove the camshaft timing chain tensioner rail as described below.
32. Cover the exposed parts of the tray with clean cloths.
33. Remove the oil pump drive chain tensioner rail and spring from the bracket on the cylinder block - note the orientation of the spring to reinstall it correctly (see fig. 8.33). Remove the bushing.
Fig. 8.33. Remove the oil pump drive chain tensioner rail (1), bushing (2) and spring (3) from the bracket on the cylinder block
34. Using a grinder, grind down the ridges on one of the links of the oil pump drive chain at the top of the sprocket. Be careful not to touch or damage the sprocket.
35. Hold the chain to prevent it from falling off the pump drive gear, then pull out the chain link plate and push the link to the back of the chain.
36. Remove the rags, preventing the metal filings from falling into the tray.
37. Hold the chain on the oil pump drive gear with a rope or wire.
38. Make alignment marks on the camshaft sprocket and timing chain, then remove the camshaft timing chain from the sprocket.
39. Remove the crankshaft sprocket from the front of the shaft using a puller. You can use two large screwdrivers on each side of the sprocket as levers. Remember the position of the sprocket to reinstall it correctly.
40. Remove the woodruff key from the shaft if it has become loose.
Examination
41. For information on how to check the crankshaft sprocket, refer to item 22.
Installation
42. Install the woodruff key onto the end of the shaft.
43. If a new sprocket is to be installed, transfer the position mark from the old sprocket to the new one.
44. To install the sprocket on the crankshaft, it must be heated to approximately 50°C.
45. When the star is approximately heated to the desired temperature (you can put the star in very hot water for a while), align the slot on the sprocket with the protrusion on the shaft and move the sprocket to the end of the crankshaft. Make sure that the sprocket is positioned as it was before removal.
46. Pass the chain around the camshaft sprocket, making sure that the marks made on the sprocket and camshaft drive chain before removal are aligned.
47. Pass the chain around the crankshaft sprocket, again making sure that the marks made on the sprocket and chain before removal are aligned.
48. Put the two ends of the oil pump drive chain on the crankshaft sprocket, then use a new link to connect the two ends of the chain. Install the link from the back of the chain and make sure the link fits into place.
49. Install the link plate and secure the plate by flattening the ends of the link pins. There is a special device for this operation, but satisfactory results can be achieved using a hammer and a metal block placed on the back of the chain. Be careful not to damage the chain or sprocket.
50. Make sure the link is securely fastened without any metal build-up or burr formation.
51. Install the timing chain tensioner rail bushing, spring and then the tensioner rail. Make sure the spring is oriented as noted before removal.
52. Install the camshaft timing chain tensioner chain as described later in this paragraph.
Guide rail
Removal
53. Turn the crankshaft so that the piston of the 1st cylinder is set to the TDC position, making sure that the valve timing marks are aligned as described in paragraph 3.
54. Remove the lower timing chain cover as described in paragraph 6.
55. Apply alignment marks to the chain and camshaft sprocket.
56. Remove the camshaft sprocket as described earlier in this paragraph.
57. Using a screwdriver, carefully release the clips and remove the outer part of the guide rail from the inner part (see fig. 8.57). Be careful as the fasteners break easily.
Fig. 8.57. Release the clamps and separate the two halves of the guide rail (shown by arrows)
58. Pull the chain forward to allow the inner portion of the rail to be removed from the bosses on the cylinder block.
Examination
59. Check the rail for wear, cracks or damage. If found, replace. Check the retainer that attaches the inner part to the outer part and replace the unit if there are signs of wear or damage or the plastic has become round.
Installation
60. Press the inner section of the rail into place on the cylinder block brackets.
61. Place the chain in place on the inside of the rail, then install the outside and secure it with the clamps. Make sure the clamps are secure and be careful not to break them.
62. Install the camshaft sprocket as described previously, making sure that the marks made during removal match.
63. Install the lower chain cover as described in paragraph 6.
Tensioner rail
Removal
64. Turn the crankshaft so that the piston of the 1st cylinder is set to the TDC position, making sure that the valve timing marks are aligned as described in paragraph 3.
65. Remove the lower camshaft timing chain cover as described in paragraph 6.
66. Apply alignment marks to the camshaft drive chain and crankshaft sprocket.
67. Rotate the tensioner rail as far as necessary to remove it from the axle (see fig. 8.67).
Fig. 8.67. Apply alignment marks (shown by arrows) on the chain and sprocket, then remove the tensioner rail
Examination
68. Check the rail for wear, cracks or damage. If found, replace.
Installation
69. Press down on the rail, making sure it is correctly positioned over the axle.
70. Make sure that the timing marks on the crankshaft and camshaft coincide with the position of the piston of the 1st cylinder at TDC, as described in paragraph 3.
71. Make sure that the marks on the chain and crankshaft sprocket made during removal match.
72. Install the lower camshaft timing chain cover as described in paragraph 6.