Clutch unit: APTC wet clutch

6.1 -

3	Clutch control pin

4	Clutch spring

5	Pressure plate

Bearing

7	Clutch plates

Nut

9	Safety washer

10	Clutch drum

Shim

Spring

Hub

Spare parts catalogue


Clutch

Caution

Bold reference numbers in this section identify parts shown in this exploded view diagram. These parts do not appear in the figures near the text.

APTC clutch unit description

The APTC system is a clutch system with follow-up torque and slipper clutch design to eliminate rear wheel hop under braking.

The system offers the following advantages:

- It eliminates the negative effects associated with heavy engine braking when down shifting thereby ensuring smooth sliding into corners (anti hop feature);

- It reduces the effort required to compress the clutch springs and disengage the clutch. The pull effort required to operate the clutch lever is reduced, while retaining good feel (follow-up torque).

In the APTC system, the two sections of the clutch drum are coupled by helical splines.

It is this special design that provides the follow-up torque and anti-hop features using the axial component of driving torque (under acceleration) and braking torque (under braking), respectively.

What happens is the clutch plate pack is compressed further under acceleration as a result of the driving torque (note that clutch spring pressure has been reduced in the new system), whereas during extreme deceleration braking torque partly removes the pressure causing the clutch plates to slip.

Before operating on the internal clutch parts, check for proper operation. Then deal with the problem in a systematic manner.

The following is a list of possible causes of clutch malfunctioning.

A clutch which does not disengage may be caused by:

-	excessive play of the control lever;

-	distorted clutch plates;

-	incorrect spring tension;

-	faulty clutch mechanism;

-	excessive wear of the drum or clutch housing.

A clutch which slips may be caused by:

-	insufficient play of the control lever;

-	worn clutch plates;

-	weakened springs;

-	faulty clutch mechanism;

-	excessive wear of the hub or clutch housing.

A noisy clutch may be caused by:

-	excessive play between the primary drive gears;

-	damaged primary drive gear teeth;

-	excessive play between drive plate tabs and clutch housing;

-	worn gear/clutch housing bearing;

-	the presence of metal particles (filings) on the gear teeth.

Disassembling the APTC system


Operations	Reference See Section
Drain engine oil	D 4, Changing the engine oil and filter cartridge
Remove the clutch cover	N 6.2, Removing the clutch cover

Unscrew the retaining screws (1) and remove the washers (2) and the springs (4) of pusher plate (5).

Pull out the pressure plate (5) with the pushrod (3). If needed, extract the bearing (6) placed on the inside of the pressure plate (5) using a suitable drift.

Screw in the three tools part no. 88713.2591 into the suitable housings on the hub (13).

Lock the clutch housing with tool part no. 88713.2556 and loosen the nut (8).

Remove the safety washer (9).

Slide the hub-plates-drum assembly out of the housing (A), use tools part no. 88713.2591.

Remove the spacer (11) from the housing.

Disassembling the hub-plates-drum assembly

Remove the three tools part no. 88713.2591.

Remove the hub (13) and the plates (7) from the drum (10). Collect the three springs (12).

Remove the plates (7) from the hub (13).

Caution

Keep the plates in the same order as originally fitted. You may find it convenient to tie the plates together while putting them on the bench.

Checking and overhauling the APTC unit

Clearance between clutch housing and drive plate

Insert the drive plate (A) in the clutch housing (B) and measure clearance (S) with a feeler gauge.

The clearance "S" must not exceed 0.6 mm.

If it does, change the plates and, if necessary, the clutch housing.

Overhauling the clutch plates

The clutch plates must not show any signs of blackening, grooves or deformation.

Measure the thickness of the drive plates (friction plates). It should not be less than 3.2 mm.

Caution

Overall thickness of the set of clutch plates should not be less than 50,2 mm.

Place the plate on a flat surface and check the amount of deformation with a feeler gauge.

Max flatness error: 0.2 mm.

Overhauling the pressure plate

Check bearing (6) condition. Change bearing if you find too much play.

Check contact surface of last driven plate. If extremely scored, apply a lapping compound (6-12 micron thick) onto a working surface and move the plate until it is perfectly flat.

Check the condition of the spring guides (A) of the pressure plate (5). Change the spring caps (2) at every overhaul.

Overhauling the pressure plate springs

Measure the length “L” of the uncompressed springs (4):

Minimum length: 41 mm.

Change any springs which are shorter than that.

Reassembling the hub-plates-drum assembly

Fit the three springs (12) on pin (A) onto drum (10).

Fit the clutch plates (7) on hub (13), start with one of the 11 driving plates (B) alternated with the 10 driven plates (C).

Fit all clutch plates (7) with hub (13) on the drum (10).

Warning

While refitting the drum (10) and hub (13), align the reference marks (D) and (E).

Insert the three tools part no. 88713.2591 and secure the hub (13) to the drum (10).

Screw in the three tools part no. 88713.2591 by hand, press with a hand on the clutch plate pack and hub (13) to overcome the springs (12) load.

Note

Screw in the three tools part no. 88713.2532 until the clutch plates are slightly loaded.

Reassembling the APTC unit

Position the spacer (11) on the housing (12).

Position the hub-plates-drum assembly inside the housing (12).

Note

Fit the last clutch plate (A) so that is it "offset" with respect to the others.

Fit the safety washer (9) to the primary shaft.

Lock clutch housing with tool part no. 88713.2556, so to hold it while tightening nut (8).

Tighten the nut (8) to the specified torque (Sect. C 3).

Remove the three tools part no. 88713.2591.

Fit the pusher plate (5) inside the hub (13).

Insert one spring (4) and one washer (2) in each recess.

Tighten the screws (1) to the specified torque (Sect. C 3) in a cross sequence.

Remove tool part no. 88713.2556.


Operations	Reference See Section
Refit the clutch cover	N 6.1, Refitting the clutch cover
Fill oil into the engine	D 4, Changing the engine oil and filter cartridge