General information
1. Camshaft, crankshaft and (except AHL engine) auxiliary shaft are driven by a toothed belt and rotate in phase. If during the repair process the timing belt is removed, the shafts will be able to rotate independently and the in-phase rotation will be broken.
2. The design of the engines discussed in this chapter is such that when the timing belt is removed, the pistons rest against the valves when the crankshaft rotates. Therefore, it is important to observe the relative positions of the crankshaft, camshaft and (if provided) auxiliary shaft with the timing belt removed. This is achieved by setting the motor to a certain position (called TDC - top dead center) before removing the timing belt and preventing the shafts from turning. For the same purpose, when repairing an engine, the engine must be installed at TDC, restoring the correct phasing of the shafts.
Note: On AHL engines, the coolant pump is also driven by the timing belt, but pump phasing is not important. On engines ADP, APT, APW. AFY, AEB and AJL, the auxiliary shaft drives only the oil pump, so its phasing also does not matter.
3. TDC - the highest point that the piston of the corresponding cylinder reaches (in a four-stroke engine twice per cycle; once on the compression stroke and once on the exhaust stroke). Usually (unless otherwise stated) this implies the TDC of the first cylinder in the compression stroke. Cylinders are numbered 1 to 4 starting from the timing belt.
4. The crankshaft pulley has a mark, which, being combined with the mark on the timing belt cover, indicates that piston No. 1 is at TDC (respectively, and the piston number 4) (pic. 2.4).
5. Camshaft sprocket (exhaust camshaft on DOHC engines) also has a TDC mark (pic. 2.5). When aligned with the mark on the small timing belt top cover or valve cover, the #1 cylinder piston is also set to TDC on the compression stroke.
6. In addition to this, the flywheel/faceplate also has marks that can be seen when the protective cover is removed from the clutch/gearbox bell. However, these marks are useless if the gearbox is removed - the return mark is on the bell.
Setting the N4 piston to TDC
7. Turn off the ignition before starting work.
8. If necessary, remove the engine top cover.
9. On the ADP engine, remember to connect the high-voltage wire of the first cylinder to the distributor cap, remove the cap and mark the position of the electrode of the first cylinder on the distributor housing. This will help determine the installation of the piston of the first cylinder at TDC by the slider.
10. Remove spark plugs as described in chapter 1A.
11. Using the crankshaft pulley bolt, turn the crankshaft clockwise. To determine compression, plug the spark plug hole of the first cylinder with a rubber stopper (will push her out with pressure). On engines with a distributor, the slider will approach the mark made in accordance with paragraph 9.
12. Continue turning the crankshaft until the TDC mark on the crankshaft pulley or flywheel/faceplate aligns with the corresponding mark on the valve cover or bell housing. To be more convincing, remove the top timing belt cover to see the marks on the camshaft sprocket.
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