General description
1. The camshaft and water pump are driven by a toothed belt from the crankshaft. The camshaft and crankshaft sprockets rotate in harmony, which ensures accurate valve timing.
2. The design of the engines described in this Section is such that if the crankshaft rotates when the toothed belt is removed, the valves may hit the pistons. For this reason, it is important to maintain the correct alignment of the camshaft and crankshaft at all times while the drive belt is removed from the engine. To do this, before removing the toothed drive belt, it is necessary to install piston No. 1 at TDC (top dead center) and block the shafts. If the engine has been removed for overhaul, the #1 piston must also be set to TDC during reassembly to ensure correct shaft alignment.
3. TDC is the highest point in the cylinder that the piston reaches. In a 4-stroke engine, each piston reaches TDC twice per cycle - on the compression stroke and on the exhaust stroke. Expression «TDC position» means cylinder #1 (located at the front end of the engine) stands at TDC on the compression stroke.
Installing piston No. 1 at TDC
4. Remove the glow plugs to make turning the crankshaft easier.
Note: On some engines, a 32mm hex is bolted to the power steering pulley to turn the engine without using the crankshaft sprocket bolt.
5. Install the socket on the crankshaft sprocket bolt and slowly turn the shaft clockwise until the alignment mark on the edge of the flywheel/drive plate aligns with the alignment rib on the clutch housing and the TDC mark on the fuel pump sprocket aligns with the mark on the pump housing. The moment when the No. 1 piston begins to move in the cylinder can be determined by the sound of air escaping from the No. 1 glow plug hole. Alternatively, remove the camshaft cover so that the lobes of cylinder #1 are visible. With both of them pointing up, piston #1 is at TDC.
Note: Due to the dynamic method of setting the injection timing (the pump rotates on the mount to make fine adjustments) The TDC mark on the fuel pump pulley may not align exactly with the mark on the pump housing.
6. If the engine is set to TDC in order to remove the toothed belt, block the camshaft in this position. To do this, remove its rear sprocket and install a special locking rod in the groove of the shaft. Unscrew the bolts of the cover mounted on the rear of the engine, then remove the sprocket (see chapter 6). On the 3D engine, also lock the fuel pump sprocket using the special locking pin.
7. It is recommended to use a special U-tool to lock the camshaft, however, a replacement can be made from a metal rod that fits snugly into the groove of the camshaft (see illustration).
8. Remove the rear sprocket and insert the end of the locking rod into the groove on the end of the camshaft (see illustrations).
9. If there is even the slightest play in the blocking rod, turn the camshaft slightly (turning the crankshaft clockwise), so that one end of the rod rests on the cylinder head. Using a feeler gauge, measure the gap between the second end of the rod and the head of the block. Now return the camshaft to its original position and remove the dipstick. Align the locking rod in the slots by inserting two feeler gauges (each is twice as thin as the measured gap) under its ends (see illustration).
10. The engine is now set to TDC.
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