All about Ford Mondeo

Top Dead Centre (TDC) for No 1 piston - locating
In-car engine repair procedures / Top Dead Centre (TDC) for No 1 piston - locating


General
1 Top Dead Centre (TDC) is the highest point in its travel up-and-down its cylinder bore that each piston reaches as the crankshaft rotates. While each piston reaches TDC both at the top of the compression stroke and again at the top of the exhaust stroke, for the purpose of timing the engine, TDC refers to the piston position (usually No 1 piston) at the top of its compression stroke.

2 It is useful for several servicing procedures to be able to position the engine at TDC.

3 No 1 piston and cylinder are at the righthand (timing belt) end of the engine (rightand left-hand are always quoted as seen from the drivers seat). Note that the crankshaft rotates clockwise when viewed from the right-hand side of the vehicle.

Locating TDC
4 Remove all the spark plugs (Chapter 1).

5 Disconnect both battery leads - see Chapter 5, Section 1 - unless the starter motor is to be used to turn the engine.

6 Apply the handbrake and ensure that the transmission is in neutral, then jack up the front right-hand side of the vehicle and support on an axle stand. Remove the roadwheel.

7 Remove the auxiliary drivebelt cover (see Chapter 1) to expose the crankshaft pulley and timing marks.

8 It is best to rotate the crankshaft using a spanner applied to the crankshaft pulley bolt; however, it is possible also to use the starter motor (switched on either by an assistant using the ignition key, or by using a remote starter switch) to bring the engine close to TDC, then finish with a spanner. If the starter is used, be sure to disconnect the battery leads immediately it is no longer required.

9 Note the two pairs of notches in the inner and outer rims of the crankshaft pulley. In the normal direction of crankshaft rotation (clockwise, seen from the right-hand side of the vehicle) the first pair of notches are irrelevant to the vehicles covered in this manual, while the second pair indicate TDC when aligned with the rear edge of the raised mark on the sump.

Rotate the crankshaft clockwise until the second pair of notches align with the edge of the sump mark; use a straight edge extended out from the sump if greater accuracy is required (see illustrations).

4.9A Do not use crankshaft pulleys first pair of notches A - align
4.9A Do not use crankshaft pulleys first pair of notches A - align second pair of notches B with raised rib on sump C . . .

4.9B . . . using a straight edge extended out from the sump (arrowed) if
4.9B . . . using a straight edge extended out from the sump (arrowed) if greater accuracy is required

10 Nos 1 and 4 cylinders are now at TDC, one of them on the compression stroke.

Remove the oil filler cap; if No 4 cylinder exhaust cam lobe is pointing to the rear of the vehicle and slightly downwards, it is No 1 cylinder that is correctly positioned. If the lobe is pointing horizontally forwards, rotate the crankshaft one full turn (360) clockwise until the pulley notches align again, and the lobe is pointing to the rear and slightly down.

No 1 cylinder will then be at TDC on the compression stroke.

11 Once No 1 cylinder has been positioned at TDC on the compression stroke, TDC for any of the other cylinders can then be located by rotating the crankshaft clockwise 180 at a time and following the firing order (see Specifications).

12 An alternative method of locating TDC is to remove the cylinder head cover (see Section 5) and to rotate the crankshaft (clockwise, as described in paragraph 8 above) until the inlet valves for the cylinder concerned have opened and just closed again. Insert a length of wooden dowel (approximately 150 mm/6 in long) or similar into the spark plug hole until it rests on the piston crown, and slowly further rotate the crankshaft (taking care not to allow the dowel to be trapped in the cylinder) until the dowel stops rising - the piston is now at the top of its compression stroke, and the dowel can be removed.

13 There is a dead area around TDC (as the piston stops rising, pauses and then begins to descend) which makes difficult the exact location of TDC by this method; if accuracy is required, either establish carefully the exact mid-point of the dead area, or refer to the timing marks (paragraph 9 above).


2018 www.fordmon.ru. All Rights Reserved.