VANOS control unit, installing| Note |
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| Incorrect installation of the VANOS control may result in damage to the engine valvetrain. |
1. Lock the camshafts and the crankshaft in TDC position with BMW special tools as described above in removal procedure. | Note |
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| The camshafts and crankshaft must be locked in the TDC position using BMW special tools no. 11 2 300 and 11 3 240. If the camshafts and crankshaft are not at TDC, the valves can contact the pistons when the engine is turned over. |
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| Be sure the secondary timing chain tensioner is locked down and the exhaust camshaft mounting bolts are loose before proceeding. |
2. Remove primary timing chain tensioner from side of cylinder head. See Fig. 37. 3. Install BMW special tool no. 11 3 390 into primary timing chain tensioner sleeve. Thread tool in finger tight to remove chain slack. 
Fig. 37. Primary timing chain tensioner (arrow). Remove tensioner slowly to relieve spring tension beneath end plug.
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| BMW special tool no. 11 3 390 is a dummy chain tensioner and simulates the function of the tensioner. |
4. Hand turn secondary sprockets clockwise (as viewed from front of engine) until sprockets contact stops. 5. Apply a small amount of liquid gasket sealer (3-Bond 1209® or equivalent) to VANOS housing alignment dowels on front of cylinder head. Install a new gasket. 6. Push VANOS piston gear cup into VANOS housing until it bottoms out in housing. Position VANOS control unit into place, but do not engage splines on gear cup. 7. Slide VANOS control unit into place, but do not engage splines on gear cup. Using a spanner tool (See Fig. 36.), turn exhaust sprocket counterclockwise (as viewed from front of engine)only enough to mesh gear cup splines with camshaft gear. Slowly push VANOS control unit towards camshaft. 8. Continue to slide VANOS unit in until it is fully seated, guiding chains in counterclockwise direction (as viewed from front of engine). Install and tighten control unit nuts and bolt. | Note |
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| It is critical that the exhaust camshaft sprocket be turned only the minimum amount necessary to engage the gear cup. If this procedure is done incorrectly, the VANOS system may not function correctly and engine damage could result. |
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