This procedure only applies to M20 and M40 engines.
Before removing the camshaft sprocket from the M40 engine, it is necessary to purchase a tool to hold the camshaft during the installation procedure (see point 12).
If your car's radio is equipped with an anti-theft system, make sure you have entered the correct code before disconnecting the battery.
If, after connecting the battery, the inscriptions on the instrument panel appear in the wrong language, refer to Section Anti-theft audio system and instrument panel language, for instructions on how to set the desired language.
Withdrawal
1. Disconnect the negative battery cable.
2. Remove timing belt covers (see Section Removal and installation of covers of a distributive belt).
3. On M40 engines, drain the cooling system (see chapter Car maintenance), then disconnect the hose, unbolt the thermostat housing and remove the thermostat (see chapter Cooling system).
4. Bring the piston No. 1 to the TDC position (see Section Bringing the piston of the first cylinder to the top dead center position (TDC)).
After setting the engine to TDC, do not rotate the camshafts or crankshafts until the timing chain is installed. If the camshaft or crankshaft is turned with the timing chain removed, the valves can hit the pistons, causing serious internal engine damage.
5. On M20 engines, the mark on the crankshaft must be aligned with the mark on the inner cover.
6. The mark on the camshaft sprocket should line up with the raised line on the cylinder head.
7. On M40 engines, apply an alignment mark on the camshaft sprocket and on the rear distribution cover for subsequent correct assembly.
8. On M20 engines, slightly loosen the two tensioner roller mounting bolts and move the tensioner towards the water pump. After loosening the tension of the distribution belt, tighten the fixing bolt.
9. On M40 engines, loosen the tensioner mounting nut and use a hex wrench to turn the tensioner clockwise. This will loosen the timing belt tension. Tighten the mounting nut to secure the tensioner in this position.
10. If you are going to install the same belt, mark it with an arrow indicating the direction of rotation.
It is not recommended to use a removed belt unless it is brand new. For M40 engines, BMW recommends replacing the timing belt every time the tensioner pulley is loosened.
11. Remove timing belt from roller (rollers) and from other stars. When removing the timing belt from engines on models that have a two-piece crankshaft hub, it can be very difficult to remove it from the hub, but it is much easier than removing the entire crankshaft hub assembly, which is attached with a very tight bolt
12. If it becomes necessary to remove the crankshaft or intermediate shaft sprocket, give the sprocket bolt while holding the sprocket stationary. To hold the sprocket, wrap it with a piece of the old timing belt (so that the side with the teeth engages with the teeth of the sprocket) or a piece of leather, then hold it with a special wrench. If there is no such key, tightly squeeze the ends of a piece of belt or leather with a clip. Before loosening the bolt, make sure you have the necessary camshaft installation tool, described in the next paragraph. Removing the timing belt from the crankshaft sprocket for the M40 engine is shown in the photo. Removing the camshaft sprocket for the M40 engine is shown in the photo.
Do not use the belt you are about to install to hold the sprocket. In addition, the camshaft sprocket must be held very securely. if it turns more than a few degrees, the valves can hit the pistons.
On M40 engines, the sprocket is not directly mounted on the camshaft with a key, since the groove at the end of the camshaft allows the sprocket to rotate a few degrees in both directions. The mounting bolt secures the sprocket to the cone after installing the camshaft using a special tool.
13. BMW's special camshaft installation tool on M40 engines is a metal plate that is placed on a square ledge next to the cams of cylinder # 1 on the camshaft - the cylinder head cover must first be removed.
14. If you were unable to purchase such a tool, you can make it at home from a metal plate. The goal is for this tool to hold the square lip on the camshaft at the right angles with respect to the top plane of the cylinder head (those. come into contact with the surface of the cylinder head cover).
15. If it becomes necessary to remove the crankshaft sprocket, loosen the crankshaft hub center bolt while holding the crankshaft stationary.
Kickback of the crankshaft hub fixing bolt requires the use of a heavy duty retainer, as this bolt is very tight. BMW has a special tool for this purpose No. 112150 (for M20 engines) or 112170 (for M40 engines). If you are unable to obtain or borrow such a tool, look at your local auto parts store or body shop for something suitable for the job. Note that tool #112170 is bolted to the back of the cylinder head and engages with the flywheel ring gear, so this tool can only be used with the transmission removed or the engine removed from the vehicle.
The photo shows a homemade tool for holding the crankshaft stationary while loosening the crankshaft pulley bolt (engine removed for better view).
On models with a two-piece hub, after removing the outer hub, you will need to remove the sprocket using a puller with a clip (available at any auto parts store). When working with the puller, screw in the crankshaft center bolt about three turns and use it as a bearing point for the center bolt of the puller.
Inspection
1. Check the timing belt for cracks, signs of wear and damage. If any of the listed defects is found, replace it.
2. Also inspect sprockets for any signs of uneven wear or damage requiring sprocket replacement.
When replacing any parts, consult your dealer to ensure that you are using compatible parts. On M20 engines, recently produced sprockets, tension rollers and timing belts are marked «Z 127». Replacing the timing belt on M20 engines implies that the latest model tensioner must also be installed, if this has not been done before.
3. Inspect the tension roller and, on M20 engines, the tensioner spring. Turn the tensioner pulley to make sure it rotates freely, without noise or play.
When installing a new timing belt, it is recommended to also install a new tensioner.
Installation
1. On the M20 engine, install the spring/tensioner so that the timing belt can be installed without tension.
2. Install the sprockets in the reverse order of removal; tighten the fixing bolts to the required torque. On M40 engines, turn the camshaft sprocket clockwise as far as the mounting groove allows, then tighten the mounting bolt with an initial torque of 1 to 3 Nm.
3. If you are installing an old belt, make sure that the arrow marked earlier to indicate the correct direction of rotation is pointing in the correct direction (the belt should rotate clockwise when looking at the engine).
4. Install the timing belt by first placing it under the crankshaft sprocket so that it wraps around the casing. Circle the belt around the rest of the sprockets.
5. Finally, put the belt on the tensioner rollers.
6. On M20 engines, loosen the tensioner bolts so that the spring tensions the belt.
7. On M20 engines, push the tensioner slightly from behind to make sure the spring is tensioning the belt. Do not tighten the bolts while pressing the tensioner; lightly tighten them only after releasing it.
8. On M40 engines, unbolt and remove the cylinder head cover, then use a special tool to secure the camshaft in the TDC position (see point 13).
9. On M40 engines, loosen the tensioner roller mounting nut and use a hex wrench to turn the roller counterclockwise until the belt is taut. The method of turning 90°to check the tension of the timing belt is not accurate enough for this engine, so it is highly recommended to get a special tool from BMW to check the tension of the belts (apply 32±2 divisions to the instrument).
10. Allen key and spring balance can also be used with sufficient accuracy.
11. Make sure that the spring scale is installed as shown in the photo, because the tensioner roller is mounted on the eccentric, otherwise the readings will be different from the real ones. The spring scale must be fixed on the hex wrench at a distance of 85 mm from the center of the tension roller, and the applied force must be 2.0 kg.
Dimension A = 85 mm.
12. Tighten the mounting nut to the required torque to secure the tensioner in position.
It is very important that the timing belt is tensioned correctly. If you overtighten it, it will hum, and besides, it can be easily damaged. If you pull it too loosely, it may «bounce» on the stars.
13. Check up correctness of alignment of distributive labels on camshaft and crankshaft.
14. Turn the crankshaft clockwise two full turns. (First, remove the setting tool from the M40 engine camshaft).
The new belt needs to be stretched. If this is not done, the belt tensioner will be too loose, and damage may result.
15. On the M20 engine, loosen the tensioner roller bolts, then tighten them to the required torque.
16. On the M40 engine, loosen the tensioner roller mounting nut and adjust the tension of the timing belt as described in paragraph 8. Finally, tighten the tensioner roller mounting nut, then fully tighten the camshaft sprocket bolt if it was previously loosened.
17. Check alignment of distribution marks again. If they are not completely aligned, remove and install the timing belt.
18. Perform the rest of the installation in the reverse order of removal.