790 chain slack? What's correct?

Discussion in 'Parallel World (790/890)' started by Greg di, Jun 26, 2020.

  1. Greg di

    Greg di Been here awhile

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    I just had to change my first rear tire and previously the dealer adjusted the slack during a maintenance for me so I am unclear as to what the actual slack should be.

    I saw the manual directions to a t, but the chain seems awfully tight for me for an off-road bike let alone any bike. several people on a Facebook group have said that the directions that KTM gives you are ridiculous and not right.

    How much slack for deflection to the bottom of the swing arm do you guys run? Right now I'm at 5 millimeters deflectionfrom chain at rest to chain pushed up towards the swingarm per the manual and it seems super tight.
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  2. danceswithmutts

    danceswithmutts Adventurer

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    I believe the manual says you're supposed to push the chain up, and if you measure at a point 25 mm behind the chain guide (there is a silver sticker on your swingarm to show you where) you should have a 5mm gap between the chain and swingarm.
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  3. Greg di

    Greg di Been here awhile

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    This I know. 5mm is barely any slack though. Seems way too tight.

    That's question...
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  4. danceswithmutts

    danceswithmutts Adventurer

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    From what you are describing, you can only have 5 mm of "wiggle" in your chain. You should be able to push the chain up so it's only 5mm away from the swingarm.
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  5. Venturer

    Venturer AKA klakeman Supporter

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    I agree with you. The instructions are hard to understand and can lead to a too tight chain. After some trial and error, I found 2 fat fingers of slack from underside of swing arm and chain is a pretty good measure. Better loose than too tight.
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  6. AdvRonski

    AdvRonski They call me......Ronski

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    There is another thread about this subject, so here is my post from that thread.
    The best way to set chain tension is to have the bike on a lift or centerstand, so the rear wheel is unweighted. Any sidestand or paddock stand simply has too much variance, depending on what kind of load or shock preload each bike has. Since there are 3 main suspension travel options, (200/240/270mm), there will be different specs for each model. Since correct chain tension is an important setting, affecting drivetrain lifespan and even suspension performance, I always determine the optimal tension for each of my bikes in the same way. Remove the rear shock, re-install the rear wheel, and block up the rear wheel so that the centerlines of the countershaft sprocket, the swingarm pivot, and the rear wheel axle are lined up in a straight line. At this point, the chain will be at it's tightest tension, so I adjust it to about 10-15mm of play. After re-installing the shock and wheel, you can now use whatever metric you prefer to note the correct chain tension for the bike. I prefer to measure by pulling the chain away from the swingarm at a particular point, as opposed to the method in the owner's manual, where you push the chain against the swingarm. My 350, 540, and 950 need a 3-finger gap for correct tension, while the 790, with 270mm travel, needs a 2-finger gap on the underside of the swingarm.
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  7. windblown101

    windblown101 Long timer Supporter

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    I think your mixing chain slack instructions from other bikes with the ones in the manual which are different. Some manufacturers specify the amount of total defection in the chain (1.25" to 2" whatever). KTM 790 instructions are not using that method at all. The 790 method specifies having the weight of the bike on the swingarm with it and the tire in the air so the tire can rotate and not give a false reading.

    Adjust chain so that the distance (gap) between the top of the chain and the bottom of the swingarm is 5mm with the chain being pushed upwards towards the bottom of the swingarm at a point 25mm (an inch) behind the chain slider. Your chain will be plenty loose if you use that method with the stock set up. The method @AdvRonski specifies is the more exact method to use but does requiring pulling the shock to get an initial reading. It's the only way to know for certain the slack is adjusted correctly if you are running non stock gearing, different length chain, etc.
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  8. Greg di

    Greg di Been here awhile

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    Thanks for the info.... I used a regular lift instead of a track stand. Even though I store the bike on a track stand. Easier to get wheel off and on. Never dawned on me.

    I'll reset it. I knew it wasn't right. That's what I asked.

    Thanks again!
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  9. kubcat

    kubcat Riding is Eudaemonic Supporter

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    I still think you are missing the point several of the others are trying to make. Maybe you did pick up their meaning, so thats good, but if not, your original post describes a very different measurement technique and given the resulting tension will likely damage the bike immediately upon riding it - we all just want you to avoid that scenario.

    Frm you first post
    That is NOT what the manual describes. Once ALL of the deflection from the chain is removed, it should remain no further from the swingarm than 5mm. Proper deflection is likely more than 25-30 mm.
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  10. Greg di

    Greg di Been here awhile

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    Thanks... I'm good.
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  11. redneckK20

    redneckK20 Been here awhile

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    Thanks for asking this question, I was unclear on it myself. Boy is it loose when it's set to what they recommend.
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  12. C/1/509

    C/1/509 Think for yourself

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    LOL - perception.
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  13. chippertheripper

    chippertheripper motorcycle junkie Supporter

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    Loose is fast.
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  14. BobcatSig

    BobcatSig Fresh Off The Couch Racing

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    Isn't the old adage for KTM chain tension to get it to where you think it's just about a right and loosen it a bit more? That seemed to be how my thumpers like the chain and the 790 seems no different.
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  15. AnasAcuta

    AnasAcuta Been here awhile

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    If it's too loose, you will hear it wacking the swing arm on trails. Very annoying.
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  16. kubcat

    kubcat Riding is Eudaemonic Supporter

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    If its just right, you will hear it wacking the swing arm on trails.

    FIFY
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  17. georgethegoat

    georgethegoat Been here awhile

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    @AdvRonski, I'm bracing myself for a smart answer rebuttal to this, but could your method for initial set up also be accomplished by using ratchet straps or some such to get the three points in line, without removing the shock or getting the motorcycle on a center stand?
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  18. windblown101

    windblown101 Long timer Supporter

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    The quick answer is "Yes". If the subframe is stout enough which is probably is. Don't get your finders or other body parts caught in the ratchet. It will be under a serious active load by the time you crank it down that far. Much less nerve wracking I would think to just pull the shock. It's two bolts and a turn on the shock bushing (which it left hand thread).
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  19. AdvRonski

    AdvRonski They call me......Ronski

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    As W101 said, it's certainly possible. Even getting it pretty close to a 3-axis alignment will give you a good idea of how tight or loose the chain is. I've done this with my 950, but I've had the shock out of the 790 several times, so it was just easier to do it that way.
    Sorry you had to brace yourself for a snarky answer, but I pretty much save those for the more arrogant folks around here.
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  20. georgethegoat

    georgethegoat Been here awhile

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    Haha, no no ... just got done reading through the suspension thread and meant that to tip my hat to your intelligence and diligence, not to assume you'd give me a wise crack answer.

    Anyway thanks to you both for confirming my thinking and your contributions overall.
    #20
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