790 Reported Clutch failures - My 12k mile examination

Discussion in 'Parallel World (790/890)' started by windblown101, Nov 10, 2019.

  1. windblown101

    windblown101 Long timer Supporter

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    FB has had a few fairly active posts regarding a handful of early clutch failures on the 790 Adventures and a few have been catastrophic in nature. I have not had any issues with mine so far but with 11.5K miles (18.5 Km) on the clock with a good chunk of that in the dirt and being a pretty heavy clutch slipper I decided to take a proactive look-see.

    What follows is what I found. It's not meant to "prove" anything. It's just a one of sample off a single 790 that I know has seen more hard use than some. I don't make my living turning wrenches so any and all opinions, theories, or conclusions expressed below should be taken with a grain of salt and I'll be happy to have anyone with more knowledge chime in!

    Opening it up: After pulling off the clutch cover I did notice a thin sticky film on the clutch pressure cap. Nothing extreme. Heat related I would guess. A sign of a bit too much heat? I don't know, but I will admit the clutch has been hammered on a bit from time to time.
    Cover off.jpg


    I went ahead and pulled the entire assembly because I wanted to take a look at the bearing and washers behind the clutch as well. Didn't see anything here that was a cause for concern and no signs of overheating.
    Clutch out.jpg

    Clutch pack:
    Clutchpack.jpg
    The outer disc did seem pretty dry but it's been about 3 weeks since the bike was run. All the inner discs and plates were moist. No extreme discoloration present IMHO and no signs of severe overheating, warping, or damage.

    Clutch basket: Nothing of note in my opinion. Very light wear. Basket springs were tight.
    outer basket 2.jpg outer basket1.jpg

    Inner hub: I do find some slight damage to inner hub - I'll be checking with a trusted local mechanic who has no dog in the fight about whether I need to consider replacing the inner hub or not. Opinions from inmates welcome.
    inner basket 1.jpg inner basket2.jpg

    Measurements:
    Clutchpack repair manual specs:
    New= 35.6mm to 36.5mm / Wear limit 34.80mm
    Mine Measured 36.07mm so in good shape there.

    Clutch Spring length repair manual specs
    43+mm.
    Mine all measured slightly under spec. The shortest one was 41.92mm. (will order fresh ones)


    Thoughts:
    I'm a bit disappointed that the clutch springs are slightly out of spec so soon. I can't think of any good reason they would be. I suspect I could throw them back in and not have any problems out of them for a long time. I'll be replacing them simply because they are out of spec.

    The chatter marks on the inner hub are bumming me out a little. I'm just gonna come out and say I suspect the QS to be the cause (pure speculation on my part). I disabled the QS as soon as I got the software downloaded by the dealer to do so but I did play with it a few days early on before I opted to disable it and keep it disabled.

    Conclusion:
    Meh... I don't see anything that causes me panic. The clutch discs are a bit thinner by design than some so they may take less abuse than heavier ones. Even though it does look like I got the clutch a bit hot a few times there was no apparent damage to any of the discs or plates and the clutch pack still measures within the "New" spec range. All in all I'm pretty ok with how the clutch has held up considering the use it's had. Would I have preferred to find ZERO issues on a 12k mile clutch? Sure, but I'll own a portion of the blame, order up a few parts to be on the safe side and be right back at it.
    #1
  2. braaap!

    braaap! Long timer Supporter

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    Clear write up @windblown101 great clear pics too. I suspect we owners need to reprogram our clutch hand / head and become more adept at using the TC better for the riding conditions we find ourselves navigating.

    An invaluable and insightful post, thanks,
    #2
  3. Salzig

    Salzig Long timer

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    I doubt the QS can cause damage on the clutch. To me those marks make me think about some sort of clamping device used for machining the hub.

    Be sure to measure the new springs: I wouldn't be surprised if they are already near or under the limit (typo in the manual?).
    The 790 clutch, as well as the 690, has a mechanical servo assistance and needs very little help from the springs.
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  4. SEK_Nick

    SEK_Nick Been here awhile

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    Maybe the "chatter marks" are a result of how PASC works? I have no real idea, simple speculation. Maybe somebody who knows more about that could comment?
    #4
  5. windblown101

    windblown101 Long timer Supporter

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    Thanks. I just figured I might not be the only one wondering how things looked in there.

    Good point about letting the TC do it's thing. I suspect there have been occasions I may have used clutch slip to get more power from the motor due to what my throttle hand was relaying to me when in fact it was the TC reducing power to the ground rather than a lack of available grunt.

    Well we're in the same boat, LOL. I don't have any real clue as to cause, just taking wild guesses. Perhaps just normal wear? I found it interesting that the marks appear on both sides (thrust & decel). I haven't looked closely at enough inner clutch hubs to know how common the wear pattern is. It looks worse in the photos than it is. I can't really feel them with a fingernail. I was being a bit anal trying to find something to worry about perhaps... ;)
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  6. AdvRonski

    AdvRonski They call me......Ronski

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    @windblown101 , I'd be very interested in how the clutch servo/slipper mechanism in the pressure plate works. It is very different than the clutch booster in the 950/990 engines, but I can't seem to find any pictures of it, or how it operates.
    #6
  7. windblown101

    windblown101 Long timer Supporter

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    That would require me to go back to school and get an engineering degree... I'm just a country boy. The whole "servo" thing KTM talks about escapes me at the moment. The slipper function is straight forward and actually beautiful in it's simplicity. There are three opposing ramps built into the inner hub and the center cap. Engine torque during acceleration cause the ramps to spin against each other in a direction that causes the inner hub and cap to clamp down on the clutch pack with a huge clamping force (which is why the clutch only needs three lightweight springs). On decel the force on the inner hub and cap are reversed and causes the cap and inner clutch hub to want to separate. Once the force is enough to overcome the three light springs the clutch starts to open and slip. You could fine tune the slipper function by changing the strength of the 3 springs if you wanted to. I took a quick little video below to show the effect in action.

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  8. justinope

    justinope Long timer

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    FWIW I took my bike in for what felt like excessive heat, dealer found "oil jet" in my clutch was out of spec (.25mm vs .30mm) on mine which was causing slipping and therefore excessive heat / wear so definitely check that out!
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  9. windblown101

    windblown101 Long timer Supporter

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    I'm surprised they said reduced oil flow was the cause of the slipping. A blocked clutch oil jet doesn't seem to cause clutch slipping or failures on other KTMs, just tougher shifting according to reports. The early clutch failures still seem to be a mystery.

    My wild ass guess at this point is that excessive slipping is the heart of the issue yet the cause seems to remain uncertain. I can think of three potential causes:

    1) Clutch adjustment: Freeplay is slightly tricky to adjust on this bike IMHO. There is the constant spring load on the actuator shaft itself, and then what starts out as the very light spring load as the clutch pack just starts to be pulled open (due to there being only three lightweight springs holding the clutch pack closed when it's not under load). Mine as I mentioned before, was very close to be too tight.

    2) Manufacturing inconsistency: It's possible I'd guess that some variance in part of the clutch assembly itself could cause the clutch pack to not achieve full clamping force and allow it to slip under load all the time and grenade early on.

    3) Plain old straight up extreme abuse while under power by the rider via the clutch lever.

    The Clutch pack is smaller than some (about 2/3's the thickness of my Triumph 800 for example). It's less robust nature may contribute to the few spectacular failures seen of the clutch discs, but this appears to only occur after the clutch has already been completely destroyed by heat.

    My take away: Make very certain clutch freeplay is correct. Use quality oil and change it often if you're a clutch abuser (like me), and if you sense the clutch slipping when it shouldn't be do not continue to ride the bike as a catastrophic failure (rather than just a toasted clutch) may be imminent.

    Looking forward to others thoughts and experiences. My clutch pack at 12k miles looks almost exactly like the clutch pack from my Tiger at similar miles when inspected > Some heat discoloration but no damage.
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  10. justinope

    justinope Long timer

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    Hmm my thought process (and dealer's) on that was less oil getting through = less lube = clutch gets hotter = starts to slip. Then overtime, excessive wear / felt heat to me the rider
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  11. windblown101

    windblown101 Long timer Supporter

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    I reckon it's possible, though the only time the clutch is generating heat is when it is slipping. ;)

    I was under the impression the main purpose of the oil was to help prevent glazing of the disks though that's an uneducated impression.
    #11
  12. Velociraptor

    Velociraptor TrackBum Super Supporter

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    My 790r has less than 2K miles and no issues so far but anyway I ordered the Rekluse torque clutch so at some point will have a look at my clutch. Will try and take some measurements. I was abusing it pretty bad over the weekend trying to get off some slippery stones in a creek bed.
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  13. Velociraptor

    Velociraptor TrackBum Super Supporter

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    Any idea where this oil jet is? I was looking on the microfiche but could not find an oil jet that I was sure was for the clutch.
    #13
  14. justinope

    justinope Long timer

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    Great question! I didn't get a chance to drop by the dealer when they were investigating it so I don't know to be honest, but it was something KTM had them check the tolerances on
    #14
  15. windblown101

    windblown101 Long timer Supporter

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    The oil jet sits recessed inside the transmission input shaft in the center of the clutch on the 790. You have to pull the clutch cover to access it.
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  16. Thumper Dumper

    Thumper Dumper Been here awhile

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    I also purchased a Rekluse and when I fit it I will check the tolerances on the old clutch pack and springs and report back.
    I have about 3500km on mine.
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  17. ramirin

    ramirin Ready to push

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    Never, we should slip the clutch even more and disable TC during offroad. TC won't get you over rocks and fallen trees if needed but with good clutch control skills 790 can go anywhere.

    Clutch is wearing part like tires, doesn't cost a fortune and easy to replace with basic tools.
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  18. justinope

    justinope Long timer

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    Did anyone have any luck with these early / pre-mature clutch failures getting KTM to cover it at all? I just went through the ringer with KTM NA over my 4k mile bike that was exhibiting excessive heat and they found in tracking down the issue that it showed signs of excessive / extreme clutch wear. Its been ridden very gently its whole life thus far, but apparently its now my bill ($700-1000) for the repair even though it's pretty clear to both them and me that there's no way this should have happened so soon in the bike's lifespan. Apparently the oil jet tolerance / spec I mentioned earlier in the thread isn't enough to warrant them admitting any kind of fault. In my mind, who knows what else could have been out of spec from the factory if that was...

    I'm super confused right now because I've never had a single clutch problem on any bike I've owned, probably because I ride my bikes pretty slowly / leisurely. Adding to that, I have no idea how to prevent this from happening again in the future (in another 4k miles I guess?) and it shoudln't be a realistic expectation from KTM that I'd have to rebuild my clutch every 4k miles.. right?!

    I'm left with the feeling that a warranty from KTM is worth about the same as toilet paper.. definitely didn't expect to have to make such a costly repair so soon. Catch me never buying a new KTM again :(
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  19. windblown101

    windblown101 Long timer Supporter

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    That sucks. What the heck are they replacing? A clutch pack is under $200.00
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  20. justinope

    justinope Long timer

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    I think thats parts + labor to be honest now that I'm looking at it a little more clearly (certainly have been seeing red since they gave me the news).

    My thought process is I'd go with a Rekluse for the replacement if possible / doing it myself since their parts will likely be tougher and potentially not fail every 3-4k miles. Even if its just the TorqDrive setup, etc. Definitely 0 chance I'd purchase the KTM pack without knowing what caused my initial problems.
    #20
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