790 Adventure R rear shock failure

Discussion in 'Parallel World (790/890)' started by [Art], Oct 19, 2019.

  1. windblown101

    windblown101 Long timer Supporter

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    I'm not certain but I seem to recall hearing of street only ridden Rs getting blown shocks. On top of that surely there are some S models getting ridden off the pavement/offroad.

    It will all get sorted eventually I reckon. It's certainly not the first shock to sit close to an external heat source.
    #41
  2. TrailTrauma

    TrailTrauma Nemophilist

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    Maybe a rad fan kit mounted nearby the rear shock? :D
    #42
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  3. Torque

    Torque Been here awhile

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    The YZ exhaust is wrapped around the shock, no cat and 50mm, as we all wish the 790 had.
    BMW did the same exact thing. Pulled the money out of the suspension components long ago.
    KTM is growing and gaining market share by building bikes like the 790. I am happy it is here.
    Notice the trend regarding the smaller factories. Sherco, GasGas, Beta all going to spring based KYB suspension and selling out of bikes.
    Really interesting times.
    #43
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  4. comac90

    comac90 Where's Charlie?

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    And, also, it appears the Xplor Pro is not experiencing the same failures as the R. If heat were the issue, riding offroad or not, seems there would certainly be failures on the S AND those who’ve gone Xplor Pro.

    Seems tuners like Konflict and the like are pointing towards issues not stemming from cat heat as the root cause.
    #44
  5. braaap!

    braaap! Long timer Supporter

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    Yeah but... the @Camel ADV heat shield is a cool bit of bling! Weighs nothing and, and... it's easy to fit :)
    #45
  6. comac90

    comac90 Where's Charlie?

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    Lol. Well, yeah.:D Don’t mistaken my ‘heat as root cause’ comment to mean a heat shield like that isn’t ‘needed’. :deal
    #46
  7. jmarleau

    jmarleau Been here awhile

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    I will assist.

    1 Shock failure in August.
    2 Local KTM dealer shipped the shock to WP.
    3 Shock returned 3 weeks later.
    4 Newly rebuilt shock re-installed.
    5 After a slow speed ride in October, I noted that the newly rebuilt shock was almost too hot to touch.
    6 Considering heat as the possible culprit. (Note possible)

    I don't think it is a stretch to consider heat as a factor. Consider the large low mounted tank that does not allow circulation around engine. Consider the heavily vented underside of the skid plate. Consider the reason KTM removed the upper part of the skid-plate just before bikes started shipping. Consider the lean fuel to air ratios. Check out the size of the cat.
    #47
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  8. Camel ADV

    Camel ADV Long timer Supporter

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  9. BronNowo

    BronNowo Been here awhile

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    it's not a rocket science, we all know what happens with oil when boiled :)
    #49
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  10. Salzig

    Salzig Long timer

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    French fries!!! :clap:dukegirl
    #50
  11. Bumpaman

    Bumpaman Been here awhile Supporter

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    Camel Adv heat shield is awesome!! 308BD9AB-52AE-4207-ADC2-CCCE2FE96261.jpeg
    #51
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  12. Torque

    Torque Been here awhile

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    Finally got my hands on a 790R.
    Will have some answers soon regarding the reason for the failures. A bit overbooked so it will be a week or two.
    Spent 12 hours on the bike yesterday and the initial inspection showed definite indicators.
    #52
  13. ramirin

    ramirin Ready to push

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    I'm pretty sure Gasgas will 'decide' to leave kyb and go with WP suspension in near future :johntm
    #53
  14. Torque

    Torque Been here awhile

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    Done working and taking a few minutes to opine regarding the shock failures. The weeks fly by.
    I have to give credit to a member here but will not until I have permission. While porting his shock piston he found behind the piston ring / band a shiny wear spot on one side only. Further inspection showed in the correct light we could see a polished spot on the shock shaft.

    Reason #1 for shock failure.
    Movement or rocking of the shaft between the seal head and the piston created by force at the clevis.

    Lets start with an earlier version of the pds shock.
    Seal head 100mm for arguments sake from one of the two pistons. Grab the clevis and have fun trying to feel side to side play in the shock shaft. That shock will resist side load heroically.

    Primitive Example:

    =------------------------------O------------------0---------------------0 PDS
    clevis = seal head O piston 0 Piston 0

    =-------------------------------O-------0 Xplor
    clevis = seal head O Piston0

    Now look at the Xplor shock with the piston seal head placement.
    Piston and seal head only a few mm from each other. Put a side load on this clevis and you may even hear a clunk. The secondary piston does not make any contact with shock body or cone.

    We are not talking about more side load, just a shock that can handle little side load.

    Reason #2 for shock failure. HEAT! Some bikes are starting to leak soon after shut down. Can you say heat sink.

    Heat
    What is the cause of the heat.
    The shock has no oil capacity. 46mm shock like the 85sx. 18mm shaft. Reservoir piston taking up a large part of the reservoir. You pour the oil out and look inside the shock to see where the rest went.
    How about the binding itself. That creates friction.
    How about that catalytic convertor. Ya like oh between 400 and 500 degrees.
    So one of my fast riders can trash shock fluid in 7 hours of ride time. By the way that is without a blanket of catalytic converter.
    Heat a piece of rubber your seals and O'rings, to 380 to 500 degrees and you have gummy bears.
    Heat a fluid up to 400 degrees and say bye bye.
    The reservoir piston is plastic. Seen them self destruct in racing situations from heat.

    Might as well break out the torch. Heat is a factor in shock longevity. Simple as that.

    So the shock needs help.
    Here are a few ideas, some we have already implemented on other xplor shocks. Others we will be implementing soon.

    Buy a heat shield. Its not that much money, is not a weight issue and it works. Or make one, just get one on there.

    Seal head designed with the bushing further from the piston. Found one but think we can make an even better one.

    Increase your travel. We can increase the travel on this bike to 270mm without issue and help the shock last longer.
    Yep
    When you are deeper in the stroke the leverage reduces because the piston is further from the seal head. Go figure, More travel more sag, less leverage.
    Makes you wonder why fast guys are not blowing shocks as much. Well they do run deeper in the stroke more of the time.

    How about the Teflon piston band. It is a looser fit than the pleather ones. I prefer teflon, but tighter piston less side to side movement for your pleather and mine. :)

    How about a bladder. Alleviate the piston friction and increase the oil capacity. Have good idea on that one and will build it soon.

    Produce a remote reservoir set up, may give that a shot as well although there are limitations or just implement a larger shock.

    Well that is my opinion and would like to hear yours.

    Oh ya and credit the majority of additional damage inside the shocks to riding the bike after the shock blows. That can destroy everything. Shock body, Piston, Seal head, shock shaft.
    #54
  15. Snowhite808

    Snowhite808 Been here awhile

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    Super good thoughts of course frome Torque.
    However some of the points will be little hard to sell, would there not be exclusions.
    My friend had a failure - the shock shaft had some serious damage on it. Also the shock body. after it blew - maybe few km were ridden.
    My shock is dripping from just sitting in the garage. No heat being built there.
    And now the exclusion - we have a known bike - with more than 25000km of road/offroad mix and some of it brutal use. Nothing wrong with that shock.
    I can totally believe the shaft problem. Also some material/seal/oillubrication/tolerance issue. But the heat- it seems to me, that heat is just a performance brake and makes the situation worse. But the shocks that want to fail, will fail even if there is no heat - we have a friend with 1900km road on the clock - failed shock and exhaust has been deprived of CAT since day one.
    And we still have no officcial answer from the manufacturer. Nor from the assembler.

    Cheers.

    #55
  16. Torque

    Torque Been here awhile

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    Agree with all that you say, very good points.

    My point still goes to the leverage with a short stroke shock. The heat is simply another ingredient in the recipe. Not necessarily cause but we all know it is bad.
    By the way I do not own the 790 that I mentioned. I spent 12 hours modifying a 790R and extending the travel.

    More to ponder?

    500 EXC uses the same shock design. 46mm, 18 shaft, same bottoming device, pistons, etc.
    Stroke 104mm
    Length 415mm
    Sag 110mm separating seal head to piston about 37mm apart. Just examples here to make the point not for accuracy.

    790S
    Stroke 71.5mm
    Length 364mm

    I did not have the time to measure the 790R bike I had as it was already a 12 hour day. But I can approximate the numbers.

    790R
    Stroke 85mm
    Length 377mm
    Sag 80mm bringing the seal head away from the piston about 26mm.

    So you have the nearly identical shock design on the exc with 11mm more separation from seal head to piston at standard sag and not having failures.

    The S shock I have not seen inside but it is more resistant to side load obviously.
    They generally do not use a teflon piston band in a lower end shock. Will have one in couple days to look at, wonder what the shaft size is.
    #56
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  17. Torque

    Torque Been here awhile

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    In addition let me think this out. If I was to shorten your shock that also would reduce the risk of shock failure. When we shorten the shock we keep it from topping out. So in turn we are keeping the seal head further from the shock piston and gaining additional leverage.
    Does this have to do with the S shocks not blowing?
    When I get in there I will let you know. I have an S available just have to commit the money and time to get into it.
    #57
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  18. Snowhite808

    Snowhite808 Been here awhile

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    Is the S version even similar to the xplor ?
    They have a completely different body. one with preload collar and one with hydraulic slip on type.
    also it seems the resevoir is a bit different. but that is just from pictures.

    PS! We have some info from WP, that there was some material problem with some shafts also. Nothing specific but one would imagine that perhaps the heat/higher rubbing level would cause some scoring on the shaft or so called "peeling" of the surface. Maybe.

    #58
  19. jmarleau

    jmarleau Been here awhile

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    You guys mention "Side Load" and Leverage allot. Is this due to gravity and the 790's laid down position of the shock? Torque mentions that this shock is closely related to the Explor in the 500EXC. Both the linked and the un-linked versions of the XC have the shock mounted almost vertical. I have an example of both versions now in my garage. So I find Torque's point interesting.

    After my shock failed, I obviously noted the complete lack of dampening and smoking oil all over the cat, but I also noted later on, a "clunking" sound at mid stroke that I assumed would be the PDS piston entering the PDS section of the shock body. (As you can see I have a very basic understanding of the system) I assume the "clunking" would indicate that the PDS piston was coming into contact with the shock body, destroying everything. Correct? Note: This "clunking" sound only occurred after the oil leak was detected. The shock functioned normal, even as I limped the bike home. The obvious "clunking" started when the bike was presented to the dealer for repair. All shock oil was drained out at this point. Again the million dollar question is: Was the shock failure caused by a lack of oil (failed shock seal) that then caused scoring and other damage, or was it a defect that failed within which then caused the lack of oil? I have no idea how you could decide which came first.

    Is there anything we can do on the Clevis ends of the shock? Some sort of upgraded Heim joint that we could press in, or something to replace the binding stock pivot, if this is the problem? The lower pivot of this design is always in contact with mud and water in its position on top of the swingarm.
    #59
  20. markverCA

    markverCA n00b

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    Thanks TT. Working thru my dealer the past couple of weeks, still haven't heard from KTM as to the resolution... new shock vs. rebuilt shock?
    #60
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