This procedure only applies to M10 and M30 engines.
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.
Withdrawal
1. Bring cylinder #1 to top dead center (TDC) compression stroke (see Section Bringing the piston of the first cylinder to the top dead center position (TDC)).
2. Remove the cylinder head cover (see Section Removal and installation of a cover of a head of cylinders). Once again, make sure that cylinder No. 1 is in the TDC position of the compression stroke and its rocker arms do not compress the valve springs.
3. Remove the top cover of the timing chain (see Section Removal and installation of covers of a distributive chain). Note the position of the camshaft timing marks, which should now be aligned. On four-cylinder engines (M10) on the camshaft flange, a risk is usually knocked out, which coincides with the protruding mark on the top of the cylinder head; also, the camshaft sprocket dowel pin hole will be at its lowest point. On M30 six-cylinder engines, a line drawn through two opposite camshaft sprocket bolts will be perfectly vertical, while a line drawn through the other two bolts will be exactly horizontal. Also, the locating pin must be in the lower left corner (pregnant «between 7 and 8 o'clock»). Before disassembly, make sure that you have correctly determined the TDC position for the camshaft, because. the correct timing of the valves depends on whether you aligned them accurately during assembly.
Because the engine is mounted at an angle in the engine bay, all vertical and horizontal adjustments must be made with respect to the crankshaft, not the ground.
4. Secure the crankshaft to the damper center bolt using a socket and ratchet, then loosen (but do not unscrew completely) four bolts securing the camshaft sprocket to the camshaft. Be very careful not to rotate the crankshaft or camshaft.
Some earlier models may have retaining tabs for the camshaft sprocket bolts. In this case, bend the tabs down before loosening the bolts. These tabs are no longer available from manufacturers and will not be needed during assembly.
5. Remove the bottom cover of the timing chain (see Section Removal and installation of covers of a distributive chain).
6. Loosen the four camshaft sprocket mounting bolts, then separate the chain from the crankshaft sprocket and carefully remove it and the camshaft sprocket from the engine. You may need to lightly pry the camshaft sprocket with a screwdriver.
Inspection
Distribution sprockets
Inspect the camshaft and crankshaft sprocket teeth for signs of wear. Each tooth is an inverted letter «V». When worn, one side of each tooth under stress will be slightly concave compared to the other side (those. one side of the letter «V» will be more concave and the letter will appear crooked). If the teeth look worn, the sprocket should be replaced.
The crankshaft sprocket is pressed onto the shaft and can be removed with a claw puller after the key and oil pump have been removed (see Section Removal, condition check and installation of the oil pump). However, BMW experts recommend pressing a new sprocket onto the crankshaft, heating it to a temperature of 80°C for M10 engines and 200°C for M30 engines. For this reason, if the crankshaft sprocket needs to be replaced, we recommend removing the crankshaft (see part Engine Component Overhaul Procedures this Chapter) and take it to a mechanical workshop to remove the old sprocket and press on a new one.
Distribution chain
The chain should be replaced if the sprockets are worn or the chain is loose (this is indicated by excessive noise during its operation). It is best to replace the chain every time the engine is overhauled. With a heavily worn chain, small grooves may form on the idler rollers. To avoid problems in the future, if you have any doubts about the condition of the chain, replace it.
Chain guide and tensioner
1. Inspect the chain guide and tensioner shoe for deep grooves resulting from contact with the chain. If they are too worn, replace them. The guides can be replaced by removing the circlips with a sharp tool or needle nose pliers.
2. Shake the tensioner plunger and listen for the ball valve to rattle. If it doesn't rattle, replace the plunger.
3. To further check the tensioner plunger, blow first through its closed end, then through the slotted end (guide). When blowing through the closed end, air must not pass through it, and when blowing through the slotted end, on the contrary, it must pass freely. If the plunger fails this test, replace it.
Installation
1. Install the tensioner shoe and chain guide if removed.
2. Temporarily fit the lower timing chain cover and vibration damper. To check the timing marks on the crankshaft. After checking the alignment of the TDC marks, remove the damper and cover.
3. Install the timing chain on the crankshaft sprocket, then on the camshaft sprocket, and passing it between the chain guide and tensioner shoe, install the camshaft sprocket on the camshaft. Check the alignment of the camshaft timing marks.
4. Perform the rest of the installation procedure in the reverse order of removal. Be sure to tighten the fasteners to the required torque.