Chain slap?

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by Martynho, May 25, 2010.

  1. Martynho

    Martynho No more Chilegringo.

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    I am concerned at the amount of chain slap on my 08 990Adv. I have set the tension correctly at about 50mm play when the rear is compressed and axle/sw brg and chainwheel aligned so dont want to go any tighter, but the chain slap sounds alarming considering there is no chain guide fitted. I am used to running chains slacker rather than tighter on my EXC's in the interests of driveline bearings but these have a chain guide of course.

    Anyone else have this also...should I just ignore it or are there any dire consequences out there waiting for me.

    BTW the OEM chain has 12K miles on it. Sprockets look good. What chain life are folks getting out there

    thanks
    #1
  2. Pantah

    Pantah PJ Fan from Boston

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    I'm at the end of my 3rd chain and none of them went past 16k miles. The rollers start falling of about 15k miles.
    #2
  3. Jaimoto

    Jaimoto Spaniard in Chile

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    50 mm play when front sprocket, swingarm axle and rear axle are aligned sounds a lot to me !!
    I assume the point of max chain tension occurs when all of the above is aligned so you don't want too much play at that point, maybe 5-10 mm.
    #3
  4. Possu

    Possu de-nOObed!

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    Look at it positively, chain slap means that the chain's not over tensioned.

    Try turning both chain adjuster bolts 1/6th of a turn at a time outwards to tighten the chain up a little.
    #4
  5. 9nine0

    9nine0 Formally NineFive0 V2

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    This is the longest point of the wheelbase, it is not possible for the chain to become any tighter then at this very point. 50mm is WAY too much slack in the chain when all is aligned. You would want 5 - 10mm max at this point

    If you have 50mm of chain slack at this point, how much do you have when the bike is on its center stand? I would imagine about 70 - 85mm?

    Readjust and I am sure that it will take care of your slapping problem
    #5
  6. BartG

    BartG Been here awhile

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    Funny you should mention this because I have the same on my 08 990. I have tried all different tensions from loose to tight and nothing helps (even though it does get worse if its to loose... I am even tempted to buy a chain guide just for this!

    I notice though it only happens at around 4000RPM and for the rest its ok, riding 2 up also changes it slightly because the chain runs a little tighter.

    If anyone has a real fix do post it! :wink:

    Any experience putting on chain guides or those runners you see on KTMtwins? does it help?
    #6
  7. Grizzz4440

    Grizzz4440 Over the Hill (Wild Bill)

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    I would think when the bike is on the center stand 50mm would be about right. Your chain is way to loose.
    #7
  8. evoluzione

    evoluzione Been here awhile

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    maybe i'm stating the obvious but look in your owner's manual and it will tell you exactly how much slack the chain should have (40mm when on the side stand if i remember correctly).
    #8
  9. Martynho

    Martynho No more Chilegringo.

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    Typo or maybe I was still dizzy after a ride....I measured the slack at the tightest point, and it was the KTM manual specified 5mm (not 50 sorry). Still I have chain slap particularly pulling higher gears from about 3000rpm and also at 4000 rpm steady throttle as mentioned earlier by someone else.

    Had this for years on EXC's and just lived with it and no ill effects.

    So comfort me or otherwise - Chain slap - got it or not?

    Chime in with your chain life, or is there a thread out there already?
    #9
  10. adiablolex

    adiablolex Lost again

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    my rollers started falling off at 50K+
    always used Meoni's (mechanic's) way: three fingers between the swingarm and chain on the sidestand, under the 8m bolt that's toward the back
    just WD40 for cleaning after dirty days
    as for the slap, it does happen when it gets on the loose side and I'd also check the slider, they're notorious for loosening off (people are also notorious for not using loctite in critical areas...:huh )
    #10
  11. carmima

    carmima All Orange :-)

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    Sorry if this has already been posted - I'm too slack to read all the replies :huh

    You might find it's caused by V-twin pulse - seriously.

    I've had a few big V-twins and they've all have done the same thing. I thought the same thing as you and kept adjusting the chain but it kept happenning!!

    Then one day while talking to a mechanic that also used to race road going V-twins, the subject came up of chain slap and he told me it was the pulse of the V-twin that caused it.

    To check whether it is pulses that are causing it, have someone ride your bike while you ride theirs...obviously you have to ride beside them on the left side...and look at the chain.
    I found on all my big V-twins the slap was most noticable at around 4000rpm.
    So have the person ride at constant throttle at around the 4000rpm range and watch the chain...you'll see it start to significantly pulse / vibrate up and down.
    If it does this, it's not chain adjustment - it's V-twin pulse :D

    Give it a try.
    #11
  12. Pete640

    Pete640 Long timer

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    Ive never had a chain slap on my 950A - make sure its adjusted as per manual and its not over long (272mm - 18 rollers IIRC). My did 525VM is brilliant - no noise and aging well. Funny about the 4000rpm comment - I think mine is happiest here with the 17/42 gearing.

    Pete:1drink
    #12
  13. carmima

    carmima All Orange :-)

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    :lol3 that's because it's not chain slap - it's caused by the vibes a V-twin engine produces and those vibes are transmitted to the chain in a form of vibration.

    Most people don't notice it - it's usually only noticed by sensitive folk :D

    If you follow the technical reasons for motor design in the world of racing (especially MotoGP) you'll have heard the experts all talking about tyre wear and the fact that V-twins are easier on the rear tyre than in-line fours because of the pulses the V-twin engine emits. As a follow-on to that Yamaha changed the firing order of it MotoGP engine and also the engine in the road going R1 to emulate the pulse of a V-twin.

    Well those pulses they're so concerned about also cause the feeling that the bike has chain slap, when it's actually vibration.
    #13
  14. Number057

    Number057 n00b

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    I am a "sensitive sound" guy and when I purchase my bike a month ago I came here to seek an answer , but it was not very specific , so I did something very simple , and it reduced my chain slap like 70%! (first check you have the chain to correct specs acording to manual), simple and cheap , I just put a 2 mm antinoise foam, the one that has one side with glue and put it in between the plastic chain slide and the suspension arm , that is it! done . it made a huge diference on my bike the sound was coming from the slap of the plastic and the arm, In my case .
    Hope it helps!
    #14
  15. Johnf3

    Johnf3 Long timer

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    Not the way I understand it, or how it has been explained by others smarter than me. The swingarm movement is an arc. Off the stand with no load is not the tightest the chain will be. The chain will be tightest when the swingarm is straight in line with the front countershaft.
    #15
  16. Katoom72

    Katoom72 Been here awhile

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    Yes, but the procedure that is described by KTM is the perfect way to set it to the right tension on the ADV. 50mm is way to lose with the 2 wheels on the ground and the bike on the centerstand.
    The point in the procedure is, that when the swingarm is in a straight line there still is enough but not to mutch play. If u put it at 50mm the chance of the chain biting in other components starts to get trivial. Certainly when u jump the bike so the chain gets maximum play. The chain also waves around when driving, look some slomo-video up from a bike with the chainside visible.
    #16
  17. Peanuts

    Peanuts Long timer

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    Different model KTM, but same principle...

    I thought I would share the theory with you..
    The idea is to remove shock (easy on KTM RFS models) and block up the rear wheel until the rear wheel spindle, swingarm spindle and gearbox output shaft are all in line.
    This is the tightest the chain will ever get to during it's travel.
    Then adjust the chain so it is has barely any free play.
    Then lower the wheel and replace the shock.
    Then check the chain play with the rear wheel off the ground.... this is the amount of play you need to adjust your chain to in the future...... so long as you still have the same size sprockets (see my comment at the bottom of page)

    1st photo shows rear wheel chocked up by 260mm of timber to bring the three shafts into line.
    The string line can just be seen
    [​IMG]
    Second photo shows a close up of the string line. Chain has only a small amount of play.
    [​IMG]
    Third photo shows the chain tension when the shock is back in and the wheel is off the ground. Three links of the chain can be pressed onto the top of the swingarm.
    It has to be this loose.
    If it were tighter the chain would be even tighter than a guitar string when the suspension is compressed. This would cause damage to the gearbox output shaft bearing, chain and rear wheel bearings.
    BTW the bike has 14:40 gearing. When I did the same procedure with 13:50 off road gearing the chain could not be pressed closer than 3mm away from the top of the swingarm. Its this dramatic difference caused by sprocket sizes that can catch out the unwary.
    [​IMG]
    #17
  18. kingrj

    kingrj Been here awhile

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    My 950 never had any noticeable chain "slap" until it was worn out. When the links started kinking and the pitch didn't match the sprockets anymore it made noise and slapped around. On my third chain now..longest one ever lasted was 17,000 miles..
    #18
  19. The Griz

    The Griz Long timer

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    You are correct. I had it reversed! My apologies. I will edit my post to reflect.
    #19
  20. The Griz

    The Griz Long timer

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    Your chain is 10-15mm too loose. It should be 35-40mm, while bike is on side stand.

    [​IMG]

    DO NOT adjust chain tension to 35-40mm while the bike is on the center stand. You're asking for trouble and excessive chain wear at minimum if you do that. When the bike is on the center stand this is the chain's loosest position. This is because the drive shaft (center of the front sprocket), swing arm axle, and rear wheel axle (center of the rear sprocket) are as misaligned as they can be. This misalignment shortens the distance between the drive shaft and the rear wheel axle, effectively making chain looser. If you set the chain tension to 35-40mm in this position it will be WAY too tight when the swing arm is in the exact center of its swing, when the drive shaft, swing arm axle, and rear wheel axle are fully aligned. The reason KTM has you put the bike on the side stand is because it loads the bike slightly and moves the swing arm more toward alignment position. True, putting the bike on it's side stand doesn't put the swing arm exactly at the aligned position, but it's closer. Also KTM have accounted for the difference between true alignment position and where the swing arm is at while the bike is on its side stand. Follow the manual specification and steps and it'll be perfect. There are those out there that adjust to 35-40mm when the swing arm is in its fully aligned position, but this would be wrong too, as the chain would be too loose. In reality, if one wanted to adjust the chain with the swing arm in its fully aligned position the chain slack would probably need to be more like 25-30mm.
    #20