You would expect the component suppliers to get their measurements right so that their parts are interchangeable with OEM parts, which will take the guess work out of it. Some manufacturers may want you to take a full kit - pressure plate, springs and caps - as these work together but may not work separately. Some manufacturers may just be lazy... Ducati have been very clever in reusing clutch technology for about 20-plus years in their dry clutches. You could take a basket / clutch plates / etc from an 888 and fit it to just about any modern dry clutch Ducati! HOWEVER... Ducati recently started toying with some of these parts in an effort to reduce the force required to engage the clutch. For example, the 1098 has different sized spring caps and I think the Hypermotard also has something different (springs?) so this is starting to muddy the water a bit now. If someone is buying and then reselling parts that they really are not sure about, or are mislead by the manufacturer or supplier that they are the correct parts, then it could be very easy for someone with a 1098 to end up with "regular" spring caps and for their clutch to become coil bound, for example. The torque figure shouldn't make a difference as this only comes into play once the spring cap is located against the clutch post and starts to tighten up. I wouldn't expect you to make more than 0.5mm worth of difference between 9nm and 25nm when torquing the clutch bolts anyway, which is not enough to cause any major problems, or certainly not the difference between a working and locked clutch. I expect the OP is having an issue in the overall spring height (E in the diagram) which is most likely being caused by a difference in the spring cap "ring" that is being used (changing the size of D in the diagram which effects E as C+D=E) which is more-or-less confirmed when he said that the springs worked fine with the original spring caps. I say this all from personal experience because, as mentioned above, I had to write specifications for replacement stainless springs to be made to replicate OEM springs exactly to ensure that they worked before they went into production. We went through lots of testing and lots of materials changes (stainless is not just stainless is not just stainless...) to get the right spring tension and spring return rates to "copy" the OEM characteristics!
Also don't forget that springs don't last forever! They will eventually lose their "springyness" and there may well be a tolerance for clutch springs in the workshop manual just like there is for fork springs! EDIT: the workshop manual should give the tolerance, as Billy says...
so would I be correct in saying that provided the clutch engages and doesn't slip, the amount I tighten the springs is not important. I can tighten them by hand with a socket til the spring is fully compressed and the screw stops turning, that's why I don't understand wrist tight!
What should happen is that you put the springs over the clutch post and the cap over the springs and the bolt into the spring cap so it engages into the clutch post... which I am sure is what you are doing You then tighten the bolt until the spring cap touches the clutch post (no bolt thread visible between the post and spring cap) and tighten to the correct torque setting. The clutch bolts are an M5 thread and "standard" torque setting for the plain steel 12.9 strength rated allen bolt is 10.3Nm dry or 7.7Nm lubed (see Metric Bolt Torque Chart). That's not very tight at all (and I doubt anyone has a fine-scale, low-end torque wrench for those kind of values!) but it basically equates to "nipped up" rather than a full grunt. If you find that the clutch will no longer operate because the springs are already fully compressed (this is "coil bound") then you will need to add a washer/spacer in between the clutch post and the spring cap until it works correctly. Remember that you need to add the same amount to each clutch post to ensure an even load! If you refer back to the diagram, your spring length was originally "C + D = E" (clutch post from pressure plate + spring cap depth) and will now become "C + X + D = E" where X is the thickness of the washer. This may be because your pack is new (extra thick!), your pressure plate is extra thick (different design) or your spring caps are too shallow (different design) or a combination of all of the above. iirc the clutch only needs about 5mm of movement to fully engage so you won't need to add a massive stack of washers!
ok, I have taken off the spring that came undone and broke the clutch cover, I needed a ratchet and don't understand how it could have undone itself. I now can see the post and I have a low end torque wrench, I am waiting for a new cover and springs to arrive, many thanks for help
