253 Flywheel friction face and rim face runout

When the flywheel is centred by the crankshaft axis, it is essential that the flywheel friction face and rim rotate perpendicularly to the crankshaft axis.

Mount the dial gauge magnetic base to the engine flywheel housing. First set the indicator pointer against the friction face of the flywheel near the outer edge (Fig. 2.10(a and b)) and set gauge to zero. Turn the flywheel one revolution and observe the amount of variation. Secondly reset indicator pointer against the flywheel rim and repeat the test procedure (Fig. 2.10(b)). Maximum permissible runout in both tests is 0.02 mm per 20 mm of flywheel radius. Thus with a 300 mm diameter clutch fitted, maximum run-out would be 0.15 mm. Repeat both tests 2 or 3 times and compare readings to eliminate test error.

2.5.4 Flywheel housing runout (Fig. 2.10(c)) When the gearbox bell housing is centred by the inside diameter and rear face of the engine flywheel housing, it is essential that the inside diameter and rear face of the housing should be concentric and parallel respectively with the flywheel.

Mount the dial gauge magnetic base to the flywheel friction face and position. Set the indicator pointer against the face of the housing. Make sure that the pointer is not in the path of the fixing holes in the housing face or else incorrect readings may result. Zero the indicator and observe the reading whilst the crankshaft is rotated one complete revolution. Reset the indicator pointer against the internally machined recess ofthe clutch housing and repeat the test procedure. Maximum permissible runout is 0.20 mm. Repeat both tests two or three times and compare readings to eliminate errors.

(a) Crankshaft and flywheel face runout Ibl Recessed flywheel runout
Flywheel Rim Dimension

Fig. 2.10(a-d) Crankshaft flywheel and clutch housing alignment

|c) Flywheel housing runout (d) Detachable bsll housing runout

Fig. 2.10(a-d) Crankshaft flywheel and clutch housing alignment

2.5.5 Detachable bell housing runout

When the gearbox bell housing is located by dowel pins instead of the inside diameter of the engine flywheel housing (Fig. 2.10(c)) (shouldered bell housing), it is advisable to separate the clutch bell housing from the gearbox and mount it to the flywheel housing for a concentric check.

Mount the dial gauge magnetic base onto the flywheel friction face and position the indicator pointer against the internal recess of the bell housing gearbox joint bore (Fig. 2.10(d)). Set the gauge to zero and turn the crankshaft by hand one complete revolution. At the same time, observe the dial gauge reading.

Maximum permissible runout should not exceed 0.25 mm.

2.6 Pull type diaphragm clutch (Fig. 2.11) With this type of diaphragm clutch, the major components of the pressure plate assembly are a cast iron pressure plate, a spring steel diaphragm disc and a low carbon steel cover pressing (Fig. 2.11). To actuate the clutch release, the diaphragm is made to pivot between a pivot ring positioned inside the rear of the cover and a raised circumferential ridge formed on the back of the pressure plate. The diaphragm disc is divided into fingers caused by radial slits originating from the central hole. These fingers act both as leaf springs to provide the pressure plate thrust and as release levers to disengage the driven plate from the drive members.

When the driven and pressure plates are bolted to the flywheel, the diaphragm is distorted into a dished disc which therefore applies an axial thrust between the pressure plate and the cover pressing. This clutch design reverses the normal method of operation by pulling the diaphragm spring outwards to release the driven plate instead of pushing it.

Owing to its configuration, the pull type clutch allows a larger pressure plate and diaphragm spring to be used for a given diameter of clutch. Advantages of this design over a similar push type clutch include lower pedal loads, higher torque capacity, improved take-up and increased durability. This clutch layout allows the ratio of the diaphragm finger release travel to pressure plate movement to be reduced. It is therefore possible to maintain the same pressure plate movement as that offered by a conventional push type clutch, and yet increase the ratio between clamp load and pedal load from 4:1 to 5:1.

\ Location dowel — Drive Strap snd rivet

Fig. 2.11 Diaphragm single plate pull type clutch

2.7 Multiplate diaphragm type clutch (Fig. 2.12) These clutches basically consist of drive and driven plate members. The drive plates are restrained from rotating independently by interlocking lugs and slots which permit axial movement, but not relative rotational spin, whilst the driven plates are attached and supported by internally splined hubs to corresponding splines formed on the gearbox spigot shaft, see Fig. 2.12.

The diaphragm spring is in the form of a dished annular disc. The inner portion of the disc is radially slotted, the outer ends being enlarged with a circular hole to prevent stress concentration when the spring is distorted during disengagement. These radial slots divide the disc into a number of release levers (fingers).

The diaphragm spring is located in position with a shouldered pivot post which is riveted to the cover pressing. These rivets also hold a pair of fulcrum rings in position which are situated either side of the diaphragm.

Whilst in service, the diaphragm cone angle will change continuously as wear occurs and as the clutch is engaged and disengaged during operation. To enable this to happen, the diaphragm pivots and rolls about the fulcrum rings. When the clutch is engaged the diaphragm bears against the outer

Fig. 2.12 Multiplate diaphragm type clutch

ring, but when disengagement takes place the reaction load is then taken by the inner ring.

As the friction linings wear, the spring diaphragm will become more dished and subsequently will initially exert a larger axial clamping load. It is only when the linings are very worn, so that the distance between the cover pressing and pressure plate become excessive, that the axial thrust will begin to decline.

2.8 Lipe rollway twin driven plate clutch (Fig. 2.13) These clutches have two circular rows of helical coil springs which act directly between the pressure plate and the cover housing, see Fig. 2.13. The release mechanism is of the pull type in which a central release bearing assembly is made to withdraw (pull out) three release levers to disengage the clutch. The clutch pressure plate assembly is bolted to the flywheel and the driven plate friction linings are sandwiched between the flywheel, intermediate plate and pressure plate facings. The central hub of the driven plates is mounted on a splined gearbox spigot shaft (input shaft). The splined end of the input shaft is supported by a ball race bearing mounted inside the flywheel-crankshaft attachment flange. The other end of this shaft is supported inside the gearbox by either ball or taper roller bearings. There are two types of pressure plate cover housings; one with a deep extended cover rim which bolts onto a flat flywheel facing and the shallow cover type in which the pressure plate casting fits into a recessed flywheel.

The release mechanism is comprised of three lever fingers. The outer end of each lever pivots on a pin and needle race mounted inside each of the adjustable eye bolt supports, which are attached to the cover housing through an internally and externally threaded sleeve which is secured to the cover housing with a lock nut. Inwards from the eye bolt, one-sixth of the release lever length, is a second pin which pivots on a pair of needle-bearing races situated inside the pressure plate lugs formed on either side of each layer.

Release lever adjustment

Initially, setting up of the release levers is achieved by slackening the locknuts and then rotating each sleeve in turn with a two pronged fork adaptor tool which fits into corresponding slots machined out of the adjustment sleeve end. Rotating the sleeve one way or the other will screw the eye bolts in or out until the correct dimension is obtained between the back of the release lever fingers and the outer cover rim edge. This setting dimension is provided by the

Twin Disc Pull Type Clutch Assembly
Fig. 2.13(a-b) Twin driven plate pull type clutch

manufacturers for each clutch model and engine application. Finally, tighten the locknuts of each eye bolt and re-check each lever dimension again.

Release bearing adjustment

Slacken sleeve locknut with a 'C' shaped spanner. Rotate the inner sleeve either way by means of the slotted adjusting nut until the recommended clearance is obtained between the bearing housing cover face and clutch brake.

i.e. 9.5mm for 355mm — 1LP 13 mm for 355 mm — 2LP 13 mm for 294 mm — 2LP

Finally tighten sleeve locknut and re-check clearance.

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  • fatimah
    What type of instrument is used to check the run out of flywheel?
    2 years ago

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