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quiet_clutch_655-1.doc - Ducati.ms

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quiet_clutch_655-1.doc - Ducati.ms

    A quiet Ducati clutch, the easy way!

    By Nick Woods

    The following modification is based on my experiences with a ‘99 ST4 clutch, initially using an OEM basket and centre/hub plus an aftermarket plate pack, and subsequently an OEM centre and Charlie

    Smith/Procutting clutch basket with matched Barnett plate pack. Other members of the Yahoo LiST have tried it with success, but we have not researched into whether it can be applied to every possible combination of OEM and aftermarket components. It is important, therefore, that you understand the principles before starting work. As with any modification, there are always pros and cons, so you do it at your own risk!

    Ducati’s dry clutch has good ‘feel’ and works well, its one main advantage over the wet clutches of other manufacturers being that dust from the friction linings does not contaminate the oil. Theoretically, the absence of friction-reducing oil might also make it possible to use lighter clutch springs, but no Ducati rider has ever seen evidence of that! Given there is no need to keep oil inside the unit, it can be run open to cool it and give it a racier look, but that is when its major attribute becomes really evident. It is loud!!

    Not a problem when the engine is actually driving the rear wheel, a heavy knocking noise is apparent when idling in neutral, and is sufficient to be quite offensive to those of a sensitive nature. (We shall ignore riders who proclaim that ‘loud clutches save lives’, as they are confused souls…) Whether the noise is objectionable or not, that mechanical mayhem does no good to the clutch itself, such that some owners prefer to ride the bike gently as it warms up, rather than let the clutch hammer itself apart.

    The noise is directly related to the dry status of the Ducati clutch, as there is no oil film to cushion necessary play in the unit. The infrequent and uneven power pulses from the beloved vee-twin also make it worse than would be the case with a four-cylinder engine, plus the Ducati is sports-orientated and does not carry a massive flywheel that would damp the pulses better.

    The knocking actually comes from the clutch plate-pack rocking to and fro in the slots of the clutch basket. The closer the clearances, as with the fabled Charlie/Barnett set-up, the quieter the unit, and having alloy tabs

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    running in alloy slots is less resonant than with the original steel on steel. However, sooner or later, the clearances will open up with normal wear, and the knocking starts…

    Several commercial suppliers have hit on a method of preventing the to-and-fro fretting of the plate-pack in the basket, and the method outlined below is based on personal experience of one of them, which utilised a special plate pack mated to the OEM ST4 basket and centre. The difference with the quietening mod that follows is that it requires nothing more than the addition of a couple of junk plates, and no machining or special components at all.

    Basically, it consists of incorporating the equivalent of a rotary friction damper to bind the entire clutch unit together, (centre, plate-pack and basket) when the clutch is fully engaged. It has no effect on clutch action, but there are some theoretical mechanical/wear disadvantages that probably explain why Ducati themselves have not adopted it. (There is some evidence that Ducati did utilise it at one stage of 900 production,

    perhaps also with the Paso, but they seem to have abandoned it subsequently).

    I’ll outline the theoretical disadvantages later but, rest assured, clutches modified in this way have given many thousands of miles of trouble-free silent service.

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    So, a step by step procedure that can produce a quiet clutch in minutes is as follows. I assume that all home Ducati mechanics are able to gain access to the clutch and remove and replace the plate-pack correctly. For this job, there is no need to remove either the clutch centre or the basket, both of which require special tools.

    Before you start, you will need to find two old friction plates, preferably of the OEM ST2/ST4 steel type, as they are stiffer than the alloy friction plates of the OEM ST4s.

    1: Remove the pressure plate and springs, and take all the loose plates out, keeping them in the order of removal. Inspect the edges of the tabs

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    on the friction plates, and the sides of the basket slots. There, you will likely see the wear caused by the tabs slamming to-and-fro in the slots. If the slots have deep notches in them, a new basket may be needed in the near future, or smooth engagement could be compromised by the tabs sticking in the grooves. I think there is little to be gained by filing the burrs off the tab sides, as this just reduces the contact surface-area again.

    2: Drop one of the old junk friction plates into the basket first, pushing it right down into the slots. As the tabs on the plate reach the radiussed ends of the slots, they will lock into the curve while pressure is applied, and cannot rattle to-and-fro. This is the first significant aspect of the mod.

3: Then add the second old tabbed friction plate.

    4: Now slide the first plain steel plate onto the clutch centre and push it as far in as it will go. For the quietening mod to work, that steel plate has to contact the face of the previous friction plate before it hits the bottoms of

    the splines/slots on the centre. The amount by which the friction face protrudes needs only to be around 0.020”/0.5mm, and more will not be

    better. This dimension will likely be different with the various options of OEM and aftermarket components you might be using, and is also influenced by any wear on the front face of the clutch centre. Checking the amount of overhang will require a short straight-edge that can be laid across the friction faces adjacent to the roots of the slots in the centre.

    5: Replace all the other plates as they came out, including the cone-shaped spring-plate, whose exact position and orientation does not seem to be critical. (Note that the wave-profiled spring plate in the Barnett plate-pack gives more resilience, and may be a factor in abolishing the famous ‘groan’ on take-up. Refacing your stock plates can apparently

    work too).

    6: Disregarding the extra two plates in the bottom of the basket, your effective plate-pack thickness should only have increased by that 0.020”/0.5mm mentioned in 4 above. This should mean there will be no

    issues with plates coming out of the basket slots or off the centre when the clutch is disengaged, especially if your plates have seen some use.

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    However, you should check this before running the bike. The specified max thickness of the pack is 38.5mm, but a mm or so less is permissible.

    If you have to juggle with plates, remember that different brands vary in thickness and number, and I see no problem with mixing-and-matching plates to get the right total thickness. If you find it difficult to get down to the 0.020”/0.5mm overhang, you could always reduce the thickness of the friction material on the two additional plates, but do it evenly on a flat surface to keep the outer surface square to the rest of the components. Finally, make sure that the very last plate you put in is a plain steel one for the pressure plate to contact.

    7: With the clutch back together, and the springs seated and tightened carefully, test the action without the engine running:-

     A: Pull the clutch lever right in with one hand, and then gently rock the pressure plate with the finger-tips of your other hand. You should see that all items (pressure-plate/centre, plain plates, friction plates and basket) are free to move independently, within their limits of play.

     B: Now start releasing the lever while still rocking to-and-fro. You will see the pressure-plate and all the plain and friction plates start to bind and move as one, but that unit will still rock within the slots of the basket.

     C: As you let the lever out finally, you should see that the whole unit goes solid, such that the tabs will no longer rock within the basket slots. Any remaining movement is now inside the gearbox.

    8: Replace the clutch cover and start the engine in neutral. Silence!!

    Now test-ride the bike with caution to check that you can find neutral as easily as before. The dimensional change with this mod should be compensated by the hydraulic actuation, but there will be slightly more lost motion as the plates bed and flex a little. If you have a problem, either abandon the mod or check ways of increasing clutch lever travel by incremental adjustment of the lever screw (Caution!), bleeding the hydraulic line or bending the lever blade out.

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Now to the theoretical drawbacks of this mod.

    A proportion of the clutch spring end-loading is now being transferred to the basket, which means that the bearing in the back of the clutch basket mount is seeing an unfamiliar endload.

    In addition, action and reaction results in loading of the alloy clutch centre against its steel retaining washer, which interface is dry. The clutch centre incorporates the cush-drive rubbers that smooth the power pulses, especially at low speed, and this loading could reduce the effectiveness of the cush mechanism and accelerate wear at this point. Personally, I can detect no difference in the feel of the power pulses before and after the mod, but there will be more wear as the centre and retainer fret against each other. Perhaps a PTFE shim at this point might be a good idea…

    I feel the wear issues are genuine, but I choose to believe that they are not significant. Many Ducati riders have covered substantial mileages using one form or another of this modification without problems, and I’m sure

    all would agree that the silence and reduced wear on the clutch tabs and slots are well worth the risk. In any case, it will take only minutes to revert to standard, should you come to decide otherwise.

    Please note that this is simply free advice from an owner/rider, and you make this mod at your own risk.

Nick Woods,

    Norfolk, UK,

    May 2006

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