There were a few questions recently on the DOCGB FB group along the lines of "help, I cant engage neutral", "my clutch makes an awful noise, what can I do?" etc., so as I have some direct experience of having to sort out my own issues from time to time with clutches and as the stock answer that many seem to give in reply on FB, along the lines of "they all do that just live with it" is wholly incorrect, I thought I'd write an article explaining the clutch on Ducatis. Additionally, in the future I can just point people to this article rather than having to rewrite everything each time.
For many who use this forum this will be basic stuff but for many many others its not basic, it wasn't for me at one stage and everyone has to have a go at it for the first time at some stage, so I wanted to put together something that would help all those people.
The component internal parts:
NB. This diagram is the clutch from a Monster 1100S 2009 MY. In principle all Ducati clutches are the same although the components in different models may have a slightly different appearance and the number of clutch plates may vary from model to model.
The clutch consists of a series of plates (Part 8) which sit around a drum (part 10) inside a basket (part 13). The clutch plates are held in place within the basket by the pressure plate (part 12) which in turn is pulled down upon the clutch pates by a number of springs (part 1) which are held in place by a bolt and collar (parts 4 & 2) which screw through the pressure plate into the clutch drum.
In its resting position the clutch plates are held against each other by the pressure of the clutch springs thus transmitting the drive from the crankshaft via the primary gears drive set (part 17) to the gearbox.
When the clutch lever at the left hand handlebar is actuated the action of pulling in the lever moves a piston within the clutch master cylinder (handlebar mounted) which pushes the hydraulic clutch fluid causing a piston in the slave cylinder (part 22) to move out. The slave cylinder piston pushes against the clutch pushrod (part 16) which passes through the crankcase of the engine and rests in a bearing in the pressure plate. As the pushrod is pushed it pushes the pressure plate against the springs, lifting the pressure plate off the clutch plates, and releasing the pressure on the clutch plates. The clutch plates then separate slightly, and it only needs to be a fraction of a mm of separation, and the drive from the engine to the gearbox is disengaged thus permitting the next gear to be selected. Releasing the clutch lever takes the pressure off the pushrod and the clutch springs push back down against the clutch plates and the drive is engaged again.
Gaining access to the clutch.
With dry clutch models it's simply a matter of removing the outer clutch cover, with wet clutch models you unfortunately will need to drain the engine oil before disassembling.
The clutch cover appears to be held in place by 6 bolts but in actual fact there are only 4 you need to remove, the two which are circled do not retain the clutch cover, the clutch cover merely fits over the heads of those bolts.
Once the cover is off you'll have access to the pressure plate and the 6 bolts that retain the springs can be removed, once they're out the pressure plate itself will just pull off to reveal the clutch plates, clutch basket and drum beneath.
NB. When reassembling the pressure plate it's good practice, once the bolts are just secured in the threads of the posts on the clutch drum, to tighten them in a criss-cross fashion so the pressure plate is pulled down onto the drum evenly. I usually just hand tighten them in the order 1,4, 2, 5, 3, 6. Hand tight is really all they need, the springs exert pressure on the collars and thus the bolts and hold them in place; the Ducati recommended torque setting for them is just 5NM, also do not apply any threadlock to them, otherwise you may find the post on the clutch drum breaks when you (or the next owner) comes to undo it.
Note that when you pull off the pressure plate the pushrod may come out with it. In the centre of the pressure plate is a bearing (part 14) in which sits a spigot (part 3). The pushrod sits in this spigot in the bearing.
Although Ducati recommend the pushrod should be removed from the slave cylinder side of the engine, often times this simply is not possible and the end of the pushrod which rests within the spigot in the pressure plate will appear to be fixed there. It’s not fixed there, it’s most likely just a small amount of corrosion or clutch dust build up which has caused it to get stuck. If it does come out with the pressure plate don’t worry, it’s not the end of the world it can be removed and put back into the tunnel it sits within. However please note, in accordance with Ducati advice it should be reinserted from the slave cylinder side (although you’ll find that in practice it’s just as easy to push it back through from the clutch side). It’s also a good idea to make sure the pushrod is free of any corrosion which may have built up on it over the years, who knows when it was last out of its housing?, Check the condition of the o-rings as well; make sure they’re intact and not damaged, broken or missing.
At this stage whilst the pressure plate is in your hand, with or without pushrod, it's a good idea to check the bearing is not seized and spins freely. It is important that it does for if it doesn't then instead of the pressure plate spinning around the pushrod the pushrod will spin and chew up the slave cylinder on the left hand side of the engine.
Once you have access to the clutch plates it is easy to remove the first few with your fingers but once you get a few out the rest are too far recessed within the basket to get at them. You can either use a pair of magnetic pick up tools to attach to them and pull them out or you can create a makeshift tool from a pair of large paper clips, bent in such a way they fit under the plates between the edge of the basket and you can hook the plates out to a position where you can get hold of them.
Order of the clutch plates.
There are two types of clutch plate; plain steel ones with teeth on the inside and toothless steel ones with pads of friction material bonded on their face. When the bike leaves the factory the clutch plates are assembled in a specific order. It is highly likely, if your bike has had previous owners, the plates may not be in the correct order. This is due to either a lack of understanding (or care) by some owners on the order they should go in, or the owner has re-ordered them in an attempt to 'fix' some issue with the clutch. The correct order, going from the inside outwards is as per the photo below.
Note there should be 2 x steel plates on the inside followed by friction, steel, friction, steel, etc., ending with one steel plate on the outside. One of the steel plates is, or should be, a dished plate i.e. it is not flat. This plate provides a small amount of 'spring' in the clutch as the plates are put under pressure and released from pressure and it contributes to smoother engagement and disengagement of the clutch.
One of the steel plates will be very slightly dished, but how can you tell which is the dished plate? Firstly it will be a plate that is 1.5mm thick. Secondly, it will have a tiny indentation punched into one face of it on the tooth opposite the semi-circle cut out in the outside circumference of the plate. Note that on clutches that have not been cleaned for a long while of clutch dust the dust can gather in, and obscure, the small indentation so do clean the plates with some scotchbrite and check very carefully. If it's not there you really ought to consider obtaining one and putting it back in the overall stack of plates.
Once you have found the plate you suspect is the dished one you can check it by holding against one of the other steel plates. When the concave side is innermost the two plates will sit flat against each other (LH photo below), when the concave side is outermost the two plates will not sit flat against each other (RH photo below).
Checking for wear on the clutch plates and basket.
Ducati recommend that the steel plates are either 2mm or 1.5mm thick with no suggested tolerance for wear on these and in reality the steel plates don't wear thin. The friction plates are 3mm thick, as measured across the friction pads when new and the recommended minimum thickness is 2.8mm, yes, just 0.2mm of wear or 0.1mm each side. Many of you will, I am sure, find friction plates inside your bike that are worn way beyond the recommended limit. In one way it's fine, the clutch will still work but you will eventually run into a problem with the clutch slipping under full acceleration.
The other place you should check is the basket itself. The tangs of the friction plates rest within the fingers of the basket and the recommended maximum gap between the edge of the friction plate tang and the side of the basket is 0.6mm. Note that if the gap is wider than this it doesn't necessarily mean the basket needs replacing just the wider the gap the noisier the 'rattle' will be as the plates have more room to slam against the fingers of the basket.
While the plates are out check the sides of the basket fingers for wear; it's not uncommon to find ridges have been gouged in the slots the friction plates rest in. The basket in the photo below is badly ridged and thus was replaced with a new one. Those ridges can prevent the free movement of the plates as the pressure exerted by the pressure plate is applied and loosened, this lack of free movement can result in the plates not separating as they should and thus not fully disengaging the drive leading to 'notchy' gear changes and difficulty finding neutral.
You will note in the photo above the basket has been removed from the clutch. To do this you will need a special clutch holding tool, I use one from Oberon but others are available. The clutch holding tool holds the basket and drum in place permitting you to undo the central retaining nut (part 25 in the parts diagram above) which holds the clutch drum in place. Note that the nut is torqued to 190Nm, so a) make sure you have a big breaker bar or suitable impact wrench and b) make sure your clutch holding tool is metal - many of the cheaper ones are plastic which have a tendency to shatter.
Clutch holding tool in place after removal of clutch drum.
The basket is held in place by 8 steel bolts, these are have a torque setting of 32 NM but will have been loctited in place. If you do remove the basket make sure you DO NOT reuse the 8 bolts, get new replacement ones and in fact any new basket you purchase will come with 8 new bolts. These are a one use only bolt.
Finally, check the 6 springs which hold the pressure plate in place are within the tolerance specified for them, i.e. measure the height of them when uncompressed. They should not be below 36.5mm, if they are they've compressed too much over the years and need to be replaced.
Once the entire clutch is disassembled clean out all the old clutch dust and rub away any corrosion with scotchbrite.
NB. If you do replace the basket or the friction plates make sure you get compatible ones i.e. if your basket is steel, as it originally would be from the factory then get steel friction plates. If you replace the basket with an alloy one then make sure you put alloy friction plates in. Steel on steel is fine, alloy on alloy is fine, but steel on alloy will lead to accelerated wear due to the differences in hardness of the materials.
Stack Height.
The stack height is the height of the full stack of clutch plates, it varies from model to model but it is the ideal height as determined by the factory in order to ensure the clutch works as intended. The correct stack height will be cited in the workshop manual for your bike, not the handbook that comes with the bike as this is supposed to be a dealer service item not a home service item. It can also readily be found online.
The photos below show the stack height of a Monster 1100S clutch (LH photo) and an ST4S clutch (RH photo), which also applies to any 748/916/996/998. The monster should be 41mm +/- 2mm and the 748/916/996/998 should be 38mm +/- 2mm.
Clutch plates come in 3 different sizes, 3mm for the friction plates and either 2mm or 1.5mm for the steel plates. Looking at the plates for the Monster above you can see there are 8 friction plates (24mm), 3 x 2mm plates (the one on the far right and the two together on the far left) i.e. 6mm plus 7 x 1.5mm plates in the middle i.e. 10.5mm giving a total of 40.5 mm, which is within the tolerance it should be. (NB the 'extra' 0.6mm shown in the above photo will be due to the dished plate slightly pushing away from the next plate in the stack.)
As the friction plates wear down the overall stack height will reduce. If each of the 8 friction plates are worn by just the recommended 0.2mm that equates to a loss of 1.6mm across the whole stack. This still would be within tolerance, remember its 41mm +/- 2mm for that particular bike, but not ideal. However, if the previous owner has let the friction plates wear beyond their recommended limit then the overall stack height will reduce beyond the recommended limits which, highly likely, will lead to clutch slip under hard acceleration.
If you are examining a clutch on a previously owned bike you may very well find some of the 1.5mm plates which the bike would have had when it left the factory have been replaced with 2mm plates. This is often done by owners to 'take up the slack' as the friction plates wear in order to keep the overall stack height at the desired level. For example, using the Monster above, as each friction plate loses material, by the time each has lost 0.1mm on each face the overall loss is 1.6mm and rather than replace the friction plates a previous owner may have had some 2mm plates lying around so they swap out 3 x 1.5mm plates for the 2mm plates and thus bring the stack height back up to much nearer the desired 41mm. The new owner then, eventually, replaces the friction plates but now the overall stack height is too high and the clutch drags and the owner complains they can't engage neutral.
Issues/problems faced by owners.
Ultimately these will boil down to four areas, clutch slip, clutch drag, clutch not disengaging and excessively noisy/rattly.
Clutch slip will most likely be due to worn clutch friction plates or worn or wrong pressure plate springs.
Clutch drag will most likely be clutch stack too high or an excessive build up of clutch dust in the body of the clutch or insufficient movement of the pushrod.
Not fully disengaging when the clutch lever is pulled in will be due to, air in the hydraulic fluid, faulty slave clyinder or master cylinder, wrong size pushrod, clutch stack too high.
Excessively noisy is solely due to too much play between the friction plate tangs and the slots in the basket they sit within.
The following is courtesy of @sev
If you use non OEM pressure plates there is the risk that it will throw out the tolerances needed in order to disengage the clutch effectively.
In isolation this isn't a problem, but when combined with RCS master cylinders and aftermarket bigger bore slave cylinders then it causes complications and resolutions along the lines of "I took four plates out and it was fine".
There are several dimensions that differ on some pressure plates from the OEM.
Don't be alarmed or worry about the tophat bush in the image above - it needs replacing due to distortion in the powerpoint cad.
As an example:
Measurement 1
The friction plate contact surface of the plate to the flat inside face of the spring cup:
OEM 3.33mm
DP 4.7mm
+1.4mm difference
In itself this one bears no relevance until you remove plates at which point its this face that will bottom out on the hub (pushrod not withstanding).
The OEM one has a bit of a rebate for the hub but the cnc plate is on one plane across the inside.
Measurement 2
Friction plate contact surface to the contact face of the pushrod top hat in the bearing housing:
OEM 21.3mm
DP 22mm
+0.7mm difference -
At the very least, the actuator rod needs to be the difference longer in order to actuate as per the OE. In practice, the feel will appear to give a shorter throw to disengage the plates - but it's all still in spec with the OEM hydraulics.
Measurement 3
Friction plate contact surface to the spring contact face:
OEM 10.13
DP 11.1
+0.8mm difference -
What this means is that the the spring is already preloaded and thus shortened.
Now couple this with a big bore slave which actually shortens the stroke and you have anything up to a 1-1.5mm shortfall in actuation before you even get started.
Bearing in mind that the OEM clutch setup moves the slave piston by circa 3.6mm.
The minute you swap the slave out with an Oberon you give up nearly 1mm of that for the lighter pull.
Its all within tolerance for the OE setup but the minute that the pressure plate is swapped out you're at the mercy of the plate designer's measurements, and in the case of the DP one I measured, it was schemed to work within the design constraints of the OE master cylinder and slave.
That's when all the various tolerances and heights start going a bit Petrovich Tong, and you end up pulling plates out of the stack like sweets.
The most important rule is to not be in a rush and only effect one change at a time if you don't know what outcome to expect.
Don't go changing everything only to find that this or that no longer works.
See how each individual component affects the thing and this learning helps your decision for the next stage.
Like all things, measure twice cut once.
The following is courtesy of @Andyb
The stack height on a std non slipper clutch isn't critical within reason due to the height of the mating face on a std pressure plate. As this has a splined boss that sits on the inner drum it can slide in and out to quite a large tolerance.
This is also who you can't/shouldnt use a pressure plate from a slipper clutch on a std clutch as that doesn't have said splines.
Summary.
Hopefully this high level overview will give readers sufficient knowledge to attempt to fix any clutch issues they have themselves. The clutch is probably one of the easiest aspects to work on and really should be within the realms of most bike owners.
I even made a couple of videos
Acknowledgements:
Ducati spa
bike-parts-ducati.com aka Ducati South London.
The Red Baron's Ultimate Ducati Desmo Manual by Edwardo Cabrera.
Larry 'Shazaam' Kelly
For many who use this forum this will be basic stuff but for many many others its not basic, it wasn't for me at one stage and everyone has to have a go at it for the first time at some stage, so I wanted to put together something that would help all those people.
The component internal parts:
The clutch consists of a series of plates (Part 8) which sit around a drum (part 10) inside a basket (part 13). The clutch plates are held in place within the basket by the pressure plate (part 12) which in turn is pulled down upon the clutch pates by a number of springs (part 1) which are held in place by a bolt and collar (parts 4 & 2) which screw through the pressure plate into the clutch drum.
In its resting position the clutch plates are held against each other by the pressure of the clutch springs thus transmitting the drive from the crankshaft via the primary gears drive set (part 17) to the gearbox.
When the clutch lever at the left hand handlebar is actuated the action of pulling in the lever moves a piston within the clutch master cylinder (handlebar mounted) which pushes the hydraulic clutch fluid causing a piston in the slave cylinder (part 22) to move out. The slave cylinder piston pushes against the clutch pushrod (part 16) which passes through the crankcase of the engine and rests in a bearing in the pressure plate. As the pushrod is pushed it pushes the pressure plate against the springs, lifting the pressure plate off the clutch plates, and releasing the pressure on the clutch plates. The clutch plates then separate slightly, and it only needs to be a fraction of a mm of separation, and the drive from the engine to the gearbox is disengaged thus permitting the next gear to be selected. Releasing the clutch lever takes the pressure off the pushrod and the clutch springs push back down against the clutch plates and the drive is engaged again.
Gaining access to the clutch.
With dry clutch models it's simply a matter of removing the outer clutch cover, with wet clutch models you unfortunately will need to drain the engine oil before disassembling.
The clutch cover appears to be held in place by 6 bolts but in actual fact there are only 4 you need to remove, the two which are circled do not retain the clutch cover, the clutch cover merely fits over the heads of those bolts.
Once the cover is off you'll have access to the pressure plate and the 6 bolts that retain the springs can be removed, once they're out the pressure plate itself will just pull off to reveal the clutch plates, clutch basket and drum beneath.
NB. When reassembling the pressure plate it's good practice, once the bolts are just secured in the threads of the posts on the clutch drum, to tighten them in a criss-cross fashion so the pressure plate is pulled down onto the drum evenly. I usually just hand tighten them in the order 1,4, 2, 5, 3, 6. Hand tight is really all they need, the springs exert pressure on the collars and thus the bolts and hold them in place; the Ducati recommended torque setting for them is just 5NM, also do not apply any threadlock to them, otherwise you may find the post on the clutch drum breaks when you (or the next owner) comes to undo it.
Note that when you pull off the pressure plate the pushrod may come out with it. In the centre of the pressure plate is a bearing (part 14) in which sits a spigot (part 3). The pushrod sits in this spigot in the bearing.
Although Ducati recommend the pushrod should be removed from the slave cylinder side of the engine, often times this simply is not possible and the end of the pushrod which rests within the spigot in the pressure plate will appear to be fixed there. It’s not fixed there, it’s most likely just a small amount of corrosion or clutch dust build up which has caused it to get stuck. If it does come out with the pressure plate don’t worry, it’s not the end of the world it can be removed and put back into the tunnel it sits within. However please note, in accordance with Ducati advice it should be reinserted from the slave cylinder side (although you’ll find that in practice it’s just as easy to push it back through from the clutch side). It’s also a good idea to make sure the pushrod is free of any corrosion which may have built up on it over the years, who knows when it was last out of its housing?, Check the condition of the o-rings as well; make sure they’re intact and not damaged, broken or missing.
At this stage whilst the pressure plate is in your hand, with or without pushrod, it's a good idea to check the bearing is not seized and spins freely. It is important that it does for if it doesn't then instead of the pressure plate spinning around the pushrod the pushrod will spin and chew up the slave cylinder on the left hand side of the engine.
Once you have access to the clutch plates it is easy to remove the first few with your fingers but once you get a few out the rest are too far recessed within the basket to get at them. You can either use a pair of magnetic pick up tools to attach to them and pull them out or you can create a makeshift tool from a pair of large paper clips, bent in such a way they fit under the plates between the edge of the basket and you can hook the plates out to a position where you can get hold of them.
Order of the clutch plates.
There are two types of clutch plate; plain steel ones with teeth on the inside and toothless steel ones with pads of friction material bonded on their face. When the bike leaves the factory the clutch plates are assembled in a specific order. It is highly likely, if your bike has had previous owners, the plates may not be in the correct order. This is due to either a lack of understanding (or care) by some owners on the order they should go in, or the owner has re-ordered them in an attempt to 'fix' some issue with the clutch. The correct order, going from the inside outwards is as per the photo below.
Note there should be 2 x steel plates on the inside followed by friction, steel, friction, steel, etc., ending with one steel plate on the outside. One of the steel plates is, or should be, a dished plate i.e. it is not flat. This plate provides a small amount of 'spring' in the clutch as the plates are put under pressure and released from pressure and it contributes to smoother engagement and disengagement of the clutch.
One of the steel plates will be very slightly dished, but how can you tell which is the dished plate? Firstly it will be a plate that is 1.5mm thick. Secondly, it will have a tiny indentation punched into one face of it on the tooth opposite the semi-circle cut out in the outside circumference of the plate. Note that on clutches that have not been cleaned for a long while of clutch dust the dust can gather in, and obscure, the small indentation so do clean the plates with some scotchbrite and check very carefully. If it's not there you really ought to consider obtaining one and putting it back in the overall stack of plates.
Once you have found the plate you suspect is the dished one you can check it by holding against one of the other steel plates. When the concave side is innermost the two plates will sit flat against each other (LH photo below), when the concave side is outermost the two plates will not sit flat against each other (RH photo below).
Note the dished plate is on the left in both photos above.
Checking for wear on the clutch plates and basket.
Ducati recommend that the steel plates are either 2mm or 1.5mm thick with no suggested tolerance for wear on these and in reality the steel plates don't wear thin. The friction plates are 3mm thick, as measured across the friction pads when new and the recommended minimum thickness is 2.8mm, yes, just 0.2mm of wear or 0.1mm each side. Many of you will, I am sure, find friction plates inside your bike that are worn way beyond the recommended limit. In one way it's fine, the clutch will still work but you will eventually run into a problem with the clutch slipping under full acceleration.
The other place you should check is the basket itself. The tangs of the friction plates rest within the fingers of the basket and the recommended maximum gap between the edge of the friction plate tang and the side of the basket is 0.6mm. Note that if the gap is wider than this it doesn't necessarily mean the basket needs replacing just the wider the gap the noisier the 'rattle' will be as the plates have more room to slam against the fingers of the basket.
While the plates are out check the sides of the basket fingers for wear; it's not uncommon to find ridges have been gouged in the slots the friction plates rest in. The basket in the photo below is badly ridged and thus was replaced with a new one. Those ridges can prevent the free movement of the plates as the pressure exerted by the pressure plate is applied and loosened, this lack of free movement can result in the plates not separating as they should and thus not fully disengaging the drive leading to 'notchy' gear changes and difficulty finding neutral.
You will note in the photo above the basket has been removed from the clutch. To do this you will need a special clutch holding tool, I use one from Oberon but others are available. The clutch holding tool holds the basket and drum in place permitting you to undo the central retaining nut (part 25 in the parts diagram above) which holds the clutch drum in place. Note that the nut is torqued to 190Nm, so a) make sure you have a big breaker bar or suitable impact wrench and b) make sure your clutch holding tool is metal - many of the cheaper ones are plastic which have a tendency to shatter.
Clutch holding tool in place after removal of clutch drum.
The basket is held in place by 8 steel bolts, these are have a torque setting of 32 NM but will have been loctited in place. If you do remove the basket make sure you DO NOT reuse the 8 bolts, get new replacement ones and in fact any new basket you purchase will come with 8 new bolts. These are a one use only bolt.
Finally, check the 6 springs which hold the pressure plate in place are within the tolerance specified for them, i.e. measure the height of them when uncompressed. They should not be below 36.5mm, if they are they've compressed too much over the years and need to be replaced.
Once the entire clutch is disassembled clean out all the old clutch dust and rub away any corrosion with scotchbrite.
NB. If you do replace the basket or the friction plates make sure you get compatible ones i.e. if your basket is steel, as it originally would be from the factory then get steel friction plates. If you replace the basket with an alloy one then make sure you put alloy friction plates in. Steel on steel is fine, alloy on alloy is fine, but steel on alloy will lead to accelerated wear due to the differences in hardness of the materials.
Stack Height.
The stack height is the height of the full stack of clutch plates, it varies from model to model but it is the ideal height as determined by the factory in order to ensure the clutch works as intended. The correct stack height will be cited in the workshop manual for your bike, not the handbook that comes with the bike as this is supposed to be a dealer service item not a home service item. It can also readily be found online.
The photos below show the stack height of a Monster 1100S clutch (LH photo) and an ST4S clutch (RH photo), which also applies to any 748/916/996/998. The monster should be 41mm +/- 2mm and the 748/916/996/998 should be 38mm +/- 2mm.
Clutch plates come in 3 different sizes, 3mm for the friction plates and either 2mm or 1.5mm for the steel plates. Looking at the plates for the Monster above you can see there are 8 friction plates (24mm), 3 x 2mm plates (the one on the far right and the two together on the far left) i.e. 6mm plus 7 x 1.5mm plates in the middle i.e. 10.5mm giving a total of 40.5 mm, which is within the tolerance it should be. (NB the 'extra' 0.6mm shown in the above photo will be due to the dished plate slightly pushing away from the next plate in the stack.)
As the friction plates wear down the overall stack height will reduce. If each of the 8 friction plates are worn by just the recommended 0.2mm that equates to a loss of 1.6mm across the whole stack. This still would be within tolerance, remember its 41mm +/- 2mm for that particular bike, but not ideal. However, if the previous owner has let the friction plates wear beyond their recommended limit then the overall stack height will reduce beyond the recommended limits which, highly likely, will lead to clutch slip under hard acceleration.
If you are examining a clutch on a previously owned bike you may very well find some of the 1.5mm plates which the bike would have had when it left the factory have been replaced with 2mm plates. This is often done by owners to 'take up the slack' as the friction plates wear in order to keep the overall stack height at the desired level. For example, using the Monster above, as each friction plate loses material, by the time each has lost 0.1mm on each face the overall loss is 1.6mm and rather than replace the friction plates a previous owner may have had some 2mm plates lying around so they swap out 3 x 1.5mm plates for the 2mm plates and thus bring the stack height back up to much nearer the desired 41mm. The new owner then, eventually, replaces the friction plates but now the overall stack height is too high and the clutch drags and the owner complains they can't engage neutral.
Issues/problems faced by owners.
Ultimately these will boil down to four areas, clutch slip, clutch drag, clutch not disengaging and excessively noisy/rattly.
Clutch slip will most likely be due to worn clutch friction plates or worn or wrong pressure plate springs.
Clutch drag will most likely be clutch stack too high or an excessive build up of clutch dust in the body of the clutch or insufficient movement of the pushrod.
Not fully disengaging when the clutch lever is pulled in will be due to, air in the hydraulic fluid, faulty slave clyinder or master cylinder, wrong size pushrod, clutch stack too high.
Excessively noisy is solely due to too much play between the friction plate tangs and the slots in the basket they sit within.
The following is courtesy of @sev
If you use non OEM pressure plates there is the risk that it will throw out the tolerances needed in order to disengage the clutch effectively.
In isolation this isn't a problem, but when combined with RCS master cylinders and aftermarket bigger bore slave cylinders then it causes complications and resolutions along the lines of "I took four plates out and it was fine".
There are several dimensions that differ on some pressure plates from the OEM.
Don't be alarmed or worry about the tophat bush in the image above - it needs replacing due to distortion in the powerpoint cad.
As an example:
Measurement 1
The friction plate contact surface of the plate to the flat inside face of the spring cup:
OEM 3.33mm
DP 4.7mm
+1.4mm difference
In itself this one bears no relevance until you remove plates at which point its this face that will bottom out on the hub (pushrod not withstanding).
The OEM one has a bit of a rebate for the hub but the cnc plate is on one plane across the inside.
Measurement 2
Friction plate contact surface to the contact face of the pushrod top hat in the bearing housing:
OEM 21.3mm
DP 22mm
+0.7mm difference -
At the very least, the actuator rod needs to be the difference longer in order to actuate as per the OE. In practice, the feel will appear to give a shorter throw to disengage the plates - but it's all still in spec with the OEM hydraulics.
Measurement 3
Friction plate contact surface to the spring contact face:
OEM 10.13
DP 11.1
+0.8mm difference -
What this means is that the the spring is already preloaded and thus shortened.
Now couple this with a big bore slave which actually shortens the stroke and you have anything up to a 1-1.5mm shortfall in actuation before you even get started.
Bearing in mind that the OEM clutch setup moves the slave piston by circa 3.6mm.
The minute you swap the slave out with an Oberon you give up nearly 1mm of that for the lighter pull.
Its all within tolerance for the OE setup but the minute that the pressure plate is swapped out you're at the mercy of the plate designer's measurements, and in the case of the DP one I measured, it was schemed to work within the design constraints of the OE master cylinder and slave.
That's when all the various tolerances and heights start going a bit Petrovich Tong, and you end up pulling plates out of the stack like sweets.
The most important rule is to not be in a rush and only effect one change at a time if you don't know what outcome to expect.
Don't go changing everything only to find that this or that no longer works.
See how each individual component affects the thing and this learning helps your decision for the next stage.
Like all things, measure twice cut once.
The following is courtesy of @Andyb
The stack height on a std non slipper clutch isn't critical within reason due to the height of the mating face on a std pressure plate. As this has a splined boss that sits on the inner drum it can slide in and out to quite a large tolerance.
This is also who you can't/shouldnt use a pressure plate from a slipper clutch on a std clutch as that doesn't have said splines.
Summary.
Hopefully this high level overview will give readers sufficient knowledge to attempt to fix any clutch issues they have themselves. The clutch is probably one of the easiest aspects to work on and really should be within the realms of most bike owners.
I even made a couple of videos
Acknowledgements:
Ducati spa
bike-parts-ducati.com aka Ducati South London.
The Red Baron's Ultimate Ducati Desmo Manual by Edwardo Cabrera.
Larry 'Shazaam' Kelly
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