Engine assembly and valve timing marks - general information and usage

Engine in-car repair procedures / Engine assembly and valve timing marks - general information and usage

General information
Note: This sub-section has been written with the assumption that the distributor, HT leads and timing belt are correctly fitted.

1 The camshaft sprocket is crankshaftdriven, by means of a timing belt, Both sprockets rotate in phase with each other and this provides the correct valve timing as the engine rotates. When the timing belt is removed during servicing or repair, it is possible for the cam and crankshafts to rotate independently of each other and the correct valve timing is then lost.

2 The design of the engines covered in this Chapter is such that potentially damaging piston-to-valve contact may occur if the camshaft is rotated when a piston is stationary at, or near, the top of its stroke.

3 For this reason, it is important that the correct phasing between the camshaft and crankshaft is preserved whilst the timing belt is off the engine. This is achieved by setting the engine in a reference condition (known as Top Dead Centre or TDC) before the timing belt is removed and then preventing the shafts from rotating until the belt is refitted. Similarly, if the engine has been dismantled for overhaul, the engine can be set to TDC during reassembly to ensure that the correct shaft phasing is restored.

4 TDC is the highest position a piston reaches within its respective cylinder - in a four stroke engine, each piston reaches TDC twice per cycle; once on the compression stroke and once on the exhaust stroke. In general, TDC normally refers to cylinder No 1 on the compression stroke. (Note that the cylinders are numbered one to four from the timing belt end of the engine).

5 The crankshaft sprocket is equipped with a marking which, when aligned with a reference marking on the timing belt cover, indicates that cylinder No 1 (and hence also No 4) is at TDC.

6 The camshaft sprocket is also equipped with a timing mark - when this is similarly aligned, the engine is correctly positioned and the timing belt can then be refitted and tensioned.

7 The following sub-Sections describe setting the engine to TDC on cylinder No 1.

Setting engine to TDC on cylinder No 1 - timing be/t fitted 8 Before starting work, disconnect the battery negative cable to disable the fuel ignition and ignition system and to remove the risk of electrical short circuits. Prevent any vehicle movement by putting the transmission in neutral, applying the parking brake and chocking the rear wheels.

9 On the distributor cap, note the position of the No 1 cylinder HT terminal. On some models, the manufacturer provides a marking in the form of a small cut-out , however if the terminal is not marked, follow the HT lead from the No 1 cylinder spark plug back to the distributor cap (No 1 cylinder is at the timing belt end of the engine) and using chalk or a pen (not a pencil, as the graphite will conduct electricity), place a mark on the distributor body directly under the terminal.

10 Remove the distributor cap, as described in Chapter 5B
11 Disconnect the HT leads from the spark plugs, noting their order of connection.

12 To bring any piston up to TDC, it will be necessary to rotate the crankshaft manually.

This can be done by using a wrench and socket on the bolt that retains the crankshaft pulley (refer to the following sub-Section for more detail).

13 Rotate the crankshaft in its normal direction of rotation until the distributor rotor arm electrode begins to approach the No 1 terminal marking made on the distributor body.

14 Carry out the following operations: a) Refer to Chapter 4A or B (as applicable) and remove the air cleaner assembly, to improve access.

b) Refer to Chapter 1 and remove the auxiliary drivebelt.

15 Prise open the clips and lift off the upper section of the outer timing belt cover to expose the timing belt sprockets beneath.

Where applicable, remove the dipstick tube and engine earth lead, if they are secured to the timing belt cover.

16 Identify the timing marks on both the camshaft sprocket and the inner section of the timing belt cover. Continue turning the crankshaft clockwise until the these marks are exactly aligned with each other. At this point, identify the timing mark on the crankshaft pulley and check that it is aligned with the ‘0’ marking on the lower section of the timing belt cover (see illustration). Note: On engine code PY, the ‘0’ marking stamped on the edge of the crankshaft pulley must be aligned with the pointer on the inner timing be/t cover.

2.16 Camshaft sprocket (A) and crankshaft pulley (B) timing marks

17 Check that the distributor rotor arm electrode is now aligned with the No 1 terminal mark on the distributor body. If it proves impossible to align the rotor arm with the No 1 terminal whilst maintaining the alignment of the camshaft timing marks, refer to Chapter 5B and check that the distributor has been fitted correctly. Note: The basic ignition advance setting may mean that the centre of the rotor arm electrode does not line up exactly with the No 1 terminal marking 18 When all the above steps have been completed successfully, the engine will be set to TDC on cylinder No 1.

Caution: If the timing belt is to be removed, ensure that the crankshaft, camshaft and intermediate shaft alignment is preserved by preventing the sprockets from rotating with respect to each other.

Setting engine to TDC on No 1 cylinder - timing belt removed 19 This procedure has been written with the assumption that the timing belt has been removed and that the alignment between the camshaft and crankshaft has been lost, for example following engine removal and overhaul.

20 On all the engines covered in this manual, it is possible for damage to be caused by the piston crowns striking the valve heads, if the camshaft is rotated with the timing belt removed and the crankshaft set to TDC. For this reason, the TDC setting procedure must be carried out in a particular order, as described in the following paragraphs.

21 Before the cylinder head is refitted, use a wrench and socket on the crankshaft pulley centre bolt to turn the crankshaft in its normal direction of rotation, until all four pistons are positioned halfway down their bores, with piston No 1 on its upstroke -i.e. 90° before TDC.

22 With the cylinder head and camshaft sprocket now fitted, identify the timing marks on both the camshaft sprocket and the inner section of the timing belt cover (refer to illustration 2.16).

23 Turn the camshaft sprocket in its normal direction of rotation until the timing marks on the sprocket and timing belt inner cover are exactly aligned. Keep the camshaft in this position and prevent it from moving.

24 Temporarily refit the crankshaft auxiliary belt pulley, then identify the timing marks on the edge of pulley and the timing belt cover.

Using a socket and wrench on the crankshaft sprocket retaining bolt, turn the crankshaft through 90° (quarter of a turn) in its normal direction of rotation, to bring the timing marks into alignment (refer to illustration 2.16) 25 Check that the distributor rotor arm electrode is now pointing roughly at the No1 cylinder terminal marking on the distributor body. If this is not the case, refer to Chapter 5B and check that the distributor has been fitted correctly. Note: The basic ignition advance setting may mean that the centre of the rotor arm electrode does not line up exactly with the No 1 terminal marking.

26 When all the above steps have been completed successfully, the engine will be set at TDC on cylinder No 1. The timing belt can now be fitted as described in Section 4.

Caution: Until the timing belt is fitted, ensure that the crankshaft and camshaft alignment is preserved by preventing the sprockets from rotating with respect to each other.