Timing Chain Idler Gear: Service and Repair

NOTE: If, on model 123 with level control, the rear bearing bushing for guide wheel shaft requires renewal, make sure that the bearing bushing on basic bore projects by 1 mm. Do not install bushing flush.

Removal





1 On model 123 with level control, unscrew pressure oil pump with lines connected and put aside.

2 Disconnect regulating linkage to remove cylinder head cover. Pull out locking eye of longitudinal regulating shaft (arrow).

Model 116.120:

Model 116.120

Model 123:

Model 123

On models 116.120 and 123, pull longitudinal regulating shaft out of rubber mount in forward direction and remove in rearward direction.

Model 126.120:

Model 126.120

On model 126.120. pull longitudinal regulating shaft out of guide lever in rearward direction and remove in forward direction.

On models 123 with automatic transmission 722.303 (W 4 A 040) and 126.120, pull out central plug for vacuum lines (71) or vacuum lines. Disconnect Bowden wire, compress black plastic clip (arrow) and pull Bowden wire out of holder in rearward direction.






3 Set crankshaft to ignition TDC.
For this purpose, rotate crankshaft by means of tool combination.






4 On engines with EGR (USA), remove pipe line between EGR valve and exhaust manifold (arrow). Unscrew shielding plate (10) for this purpose.






5 Unscrew closing plug of chain tensioner.

Attention! Closing plug is under pressure of compression spring.






6 Remove compression spring in chain tensioner.






7 Mark camshaft sprocket and timing chain in relation to each other.










8 Remove slide rail in cylinder head.
Pull out bearing bolt by means of impact puller.






9 Remove camshaft sprocket.
For loosening necked-down screw, apply counterhold to camshaft sprocket by means of a screwdriver or steel bolt.






10 On engines 617.950/951, unscrew closing plug (arrow).






96a Guide wheel
108 Closing plug
109 Sealing ring
110 Shaft






11 Pull out shaft (110) by means of impact puller and remove guide wheel (98a) in upward direction.






12 On model 123 with level control, unscrew locking screw of front bearing bushing (arrow).

Pull out shaft together with bearing bushing and remove guide wheel.

Installation
13 Position guide wheel and slip in shaft. On model 123 with level control, screw in bearing bushing locking screw (arrow in Fig. step 12).
14 Screw in closing plug with new sealing ring.






On model 123 with level control, screw on pressure oil pump with new gasket

15 Mount camshaft sprocket, while paying attention to color marks.

Tighten necked-down screw to 80 Nm. For this purpose, apply counterhold to camshaft sprocket by means of a screwdriver or steel bolt.

16 Install slide rail.






17 Rotate crankshaft and check adjusting mark in TDC position of engine.






18 Insert compression spring into chain tensioner and tighten closing plug to 90 Nm.
19 On engines with EGR (USA), install shielding plate and pipe line (Fig. step 4).
20 Mount cylinder head cover.