242Flywheel and pressure plate facing inspection

Cast iron flywheel or pressure plate faces should have a smooth polished metallic appearance, but abnormal operating conditions or badly worn driven plate linings may be responsible for the following defects:

Drive plate Limiting stop

Torsional damper spring

Splined hub

a) Overheated clutch friction faces can be identified by colouring of the swept polished tracks. The actual surface temperatures reached can be distinguished broadly by the colours; straw, brown, purple and blue which relate to 240 °C, 260 °C, 280 °C and 320 °C respectively.

b) Severe overheating will create thermal stresses within the cast iron mass of the flywheel and pressure plate, with the subsequent appearance of radial hairline cracks.

c) Excessively worn driven plate linings with exposed rivets and trapped work-hardened dust particles will cause scoring of the rubbing faces in the form of circular grooves.

2.5 Clutch misalignment (Fig. 2.10(a d)) Clutch faults can sometimes be traced to misalignment of the crankshaft to flywheel flange joint, flywheel housing and bell housing. Therefore, if misalignment exists, the driven plate plane of rotation will always be slightly skewed to that of the restrained hub which is made to rotate about the spigot shaft's axis. Misalignment is generally responsible for the following faults:

1 Rapid wear on the splines of the clutch driven plate hub, this being caused mainly by the tilted hub applying uneven pressure over the interface length of the splines.

2 The driven plate breaking away from the splined hub due to the continuous cyclic flexing of the plate relative to its hub.

3 Excessively worn pressure plate release mechanism, causing rough and uneven clutch engagement.

4 Fierce chattering or dragging clutch resulting in difficult gear changing.

If excessive clutch drag, backlash and poor changes are evident and the faults cannot be corrected, then the only remedy is to remove both gearbox and clutch assembly so that the flywheel housing alignment can be assessed (Fig. 2.10).

2.5.1 Crankshaft end float (Fig. 2.10(a)) Before carrying out engine crankshaft, flywheel or flywheel housing misalignment tests, ensure that the crankshaft end float is within limits. (Otherwise inaccurate run-out readings may be observed.)

To measure the crankshaft end float, mount the magnetic dial gauge base to the back of the flywheel housing and position the indicator pointer against the crankshaft flanged end face. Zero the dial gauge and with the assistance of a suitable lever, force the crankshaft back and forth and, at the same time, observe the reading. Acceptable end float values are normally between 0.08 and 0.30 mm.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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