How to replace starter sprag on KTM 950/990 (LC8) - write up

Discussion in 'Dakar champion (950/990)' started by keener, Apr 5, 2014.

  1. keener

    keener Speed changes you.

    Joined:
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    Ignition system finally failed. In the worse place I could imagine. After trailing my bike 1200km to West Virginia from Toronto to ride TET . It failed right at the mouth of the trail:rofl

    Symptoms:

    When you hit the started, it spins freely without engaging the engine. You might get some sporadic engagements. Once it begin to fail, you could start the bike but it skips with a stange loud bang sound. This is not to be mixed up with the torque limiter issue on early LC8. It will get worse to a point that it wont engage at all. All you hair is a whurrrrrrrr sound :huh. it spins and spins... This might also happen if the srag is installed back ward! Daugh!:trp

    Rocking the bike back and forth in gear to get the sprag grab might help.

    After some research here, I was sure the culprit is the starter "sprag" clutch. There is no post that walks you through the whole thing. Information is spread all over the place.

    How to replace the sprag:

    LC8 part comes with the whole flywheel,... that you don't need and of course it costs $575+. I learned form this post that LC4 engines use similar sprag that is made of exact same parts as in LC8. The housing is different but internals (beans + springs) are the same. And yes you can buy this for LC4 by itself from KTM :) save $500.

    If you don't know what a starter sprag clutch is learn more here: https://en.wikipedia.org/wiki/Sprag_clutch

    in short its a one way clutch around the crank shaft that grabs the crank shaft like a vise grip only when it is rotated clockwise (or counter clock wise I don't remember which way). It allow the crank shaft to speed up faster than the starter as the engine starts but not force the start to turn faster.

    Disassembling:

    - Lean the bike just a bit to the right side. I did this by putting a 2x4 under the left leg of the centre stand. This is enough to prevent any oil lose when you take the generator cover off. No mess.

    - Take the generator cover off. Some bolts are longer, two have copper washers (either side of the hose) and one that also holds two wires has a steel washer, remember where they go.

    - Pull the crank shaft breather hose down a bit to give yourself some slack. No need to take the hose off. zip tie it somewhere out of your way.

    - One large gear (torque limiter) can fall off. It may stay on the cover. Remove it.

    - This is a good time to replace the crank shaft seal (KTM part# 0760122050 ). that is on the generator cover. Its not necessary to replace it for this job. . When this seal fails, you will get excessive oil spitting out of your crank shaft hose over the front carb. The seal is cheap. You will damage the old one during take off. You can press the new one in with a plastic hammer and a 14mm socket

    - Now, the toughest part. Taking the the flywheel off. That big ass bolt in the middle is tightened to 150nm torque and has a boat load of loctite 243 (Blue). You WILL need a pneumatic impactor gun or something similar. Trying to loosen it with a wrench is nearly impossible because you will turn the engine. The impactor gun is the way to go.

    Do not use the engine locking tool, ok? its tip might break inside. Manual does not call for it during disassembling. It calls for it during assembly when you will torque the bold.

    Some say don't use heat, some say do....Old manuals says use heat and make sure the flywheel won't get hotter than 80C:deal I would try opening it without heat first and see what happens. If it didn't budge, then use a heat gun or a hair dryer. You want to heat up the bolt and not the flywheel. There are wax and glue inside the flywheel around the magnets. You don't want to melt those. Holding a soldering gun on the bolt might help too. Get someone is holding the rear break and bike is in 6th gear.

    Mine opened up nicely after heating it up. The bolt was too hot to hold in hand but the flywheel was just warm.

    You will need a 14mm allen key. I use a T-70 torx socket because that's what I had. It worked just fine.


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    - Clean the flywheel and the bolt form dried loctite.
    You will have another chance once the flywheel is out. This is only to clear the path for special tools in the next step.
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    I held a vacuum close while cleaning doing this so the debris won't go in the crank shaft,... not sure if this is needed.

    - Taking the flywheel off.
    This is the part you either need to make tools or pay money to KTM for "special tools". I went half way. Bought one and made the other. They are just two screws, nothing's special about them. One is a normal M20 bolt, 30mm hex head. The other is a M16 grub screw. I bought the M20 form KTM.

    Edit: The M16 x31mm grub screw (push screw) has different thread pitch for 950 and 990.
    For 990 needs a M16 x 1.50 grub screw
    For 950 and some older 990 needs a M16 x 2.0 grub screw

    The length of the grub screw is not critical.

    M16, 31mm long socket head – 2.0mm thread pitch KTM part # 60029009010 “PUSH SCREW F. FLYWH. EXTRACTOR “


    Grub screw is more expensive than the other tool at around $30. KTM did not have this in stock anywhere in Canada. I asked a dealer to show it to me:


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    I bought a longer M16 screw with 2mm pitch and cut it at about 31mm. Then I made a cut on the top for a flat head screw driver. It worked great.

    BTW, this is the same thread as your flywheel screw that you just took out. One might just buy a new flywheel screw and cut the head of the old !

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    The second tool (black bolt) was available from KTM and not too expensive so I bought it.

    M20 wirh 1.5 thread pitch. Its 50mm long but it a shorter bolt will do. Reference : geft post here: http://www.advrider.com/forums/showp...7&postcount=22

    part# 60029009000 FLYWHEEL EXTRACTOR (about $15)

    This one is the same for all LC8 engines.

    You can also get it from Motion Pro it seems : http://www.motionpro.com/motorcycle/partno/08-0085/
    ref: http://www.advrider.com/forums/showt...=744557&page=2


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    Here are two the tools side by side:


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    Drive the grub (push) screw in the crank shaft. No too far in. It just needs to clear the larger diameter threads for the other tool. Then screw in the big screw over it (Flywheel extractor). The big screw will force the flywheel out. You might want to use the impact gun here again. For that you will need a 30mm socket.
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    - Before taking the flywheel out you might want to loosen the 6 screw holding the spag. I didn't and I had to nervously put the flywheel on the vise with lots of rubber padding. These screws are supposed to NOT come off or else.... I found out they where nearly finger tight!!!! see: http://www.advrider.com/forums/showt...1#post23862711

    You are supposed to replace the bolts as per the manual.

    There is a little discrepancy here between the service manual and parts list. Parts list indicates the strength as 10.9 but on the service manual it says “always use 12.9 strength”
    KTM#0984060166 (AH SCREW DIN6912 M6X16 10.9)

    There is loctite 648 (green) on these bolts. Take your time to clean and degrease them and the holes very very well. I tried different methods to clean the holes. Finally the best way was using a 6mm tap with 1mm pitch. It works great. Be careful with the tap, its made of harder material. Use your finger with the tap not a driver.
    [​IMG]
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    The sprag, the culprit
    It looked bad. First I thought the ring spring failed. But thinking about it later I guess the spring is just there to hold the breans together for assembly. Its the beans that failed due to wear.

    The beans will lock into each other and grab the crankshaft when the flywheel is turned by the started (not sure clockwise or counter clockwise).

    Take the LC4 sprag apart and transfer the beans with the spring into your LC8 sprag housing. The only thing different between the two parts is the housing. The rest is identical. Note the direction of the beans!!! They all have a cut indicating their direction. Take photos. If you install the sprag backward, or install the beans backwards, it will not engage. Starter will spin freely.

    LC4 sprag part# 58440026000 FREE WHEEL FWD 332008 BLS

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    New vs. Old:
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    Note the direction of the beans:
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    - Loctite 648 (THREAD COMPOUND) – Green

    Use Loctite 648 Retaining Compound. Given how important it is that these screws not come of I would not use anything else see: (http://www.advrider.com/forums/showthread.php?t=826854)

    It is called retaining compound as supposed to Threadlock.
    It was hard to find. Only one shop locally had it in Toronto (https://www.acklandsgrainger.com). Napa could order it in. This part see lots of shocks from the starter. Red loctite 272 threadlocker (as some have suggested) may be harder, but not be able to tolerate the shocks. Use lots of it. Read KOTH post here : http://www.ktm950.info/how/wotf/wotf.html under “Ignition Rotor”

    If these bolts come off, they will destroy your stator. KTM issued tech bulletin TB 0535 in October 2004 to clean with contact cleaner and apply 648 on these bolts.
    http://forum.soe.se/attachment.php?attachmentid=8686&d=1129153271


    This photo is off other threads showing what can happen if these bolts come off:
    [​IMG]
    Picture from this thread:http://www.advrider.com/forums/showt...9#post13454989

    Scary eh? use loctite 648. No short cuts.

    BTW, do check the expiry date on the bottle!
    [​IMG]
    use it on the 6 small screws and the mating surface:
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    My 2004 old manual, calls for 13nm torque for these bolts , the tech bulletin says and newer manuals say 15nm for all year models. Torque to 15nm.

    Put it back together the way you found it.
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    - Use lots and lots of blue loctite 243 on the crank shaft bold. I put some on the crankshaft flange. EDIT: It was not necessary as I was told later.
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    EDIT: unlike what is shown in this photo, don't add loctite to the mating surface. Put it on threads only.
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    Put the engine lock tool in on the other side just how its done during valve clearance check
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    Torque the big big screw to 150nm. Get someone to hold the rear break with bike in the 6th gear.
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    - Put the cover back on and torque all screws to 10nm, crosswise.


    You are done.


    Just a final note. Resist the urge to start the motor right away. Give it at least couple of hours if not over night to allow the loctite 648 and 243 compounds to set.

    By the way, I might have refereed to free wheel as fly wheel here. Manual calls it free wheel but there is a Fly Wheel extractor tool in parts list. Call it whatever you like.

    This is got to be the longest post I've ever wrote.
    Good luck!


    p.s. To all the KTM gurus, if you see anything out of place please let me know.


    More photos: https://seeker.smugmug.com/Motorcycle...pair/i-Smv3Grd
    #1
    outbacktm likes this.
  2. Chuckracer

    Chuckracer Jerkus Maximus

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    Nice job - Thank You!
    #2
  3. rossguzzi

    rossguzzi 990 Adv.

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    Sticky this ?

    Or inc in HOW ?

    Well done.
    #3
  4. StevenD

    StevenD Hmmmm, dirt!

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    Really nice write-up!
    The only thing I disagree with is the blue loctite on the crankshaft cone. That has no place there and will only be a lot of messy stuff behind and near bearrings and all.. the amount of 243 on the bolt is also overdoing it a bit (lot)

    Verstuurd vanaf mijn LG-D802 met Tapatalk
    #4
  5. gefr

    gefr Life is a trip

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    I noticed the same to the OP.
    There is no mention of Loctite 648 for the cranckshaft cone, or the large flyweel bolt. Seems KTM believes Loctite in there could act as a lubricant and would cancel friction between cranckshaft and flyweel. My mechanic used Loctite 648 to both cranckshaft and flywheel bolt some 7 years ago. Opening it a month ago, I found the cranckcase had slipped slightly, distorting the 6 bolts. OTOH can we let these surfaces without Loctite?
    #5
  6. keener

    keener Speed changes you.

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    Interesting, when I took the crank bolt out it had a ton of blue loctite on it. I put loctite on the mating surface because I thought it won't make it harder during the removal but it will help making a tighter seal therefore reduces the risk of slippage. My thinking is that it won't hurt. Just for the record, manual asks for blue loctite on the crank shaft bolt not 648.
    #6
  7. keener

    keener Speed changes you.

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    [​IMG]
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  8. keener

    keener Speed changes you.

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    The crank shaft seal part# is 0760 122050
    #8
  9. Sporting Wood

    Sporting Wood I

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    Awesome write up, Keener! This is more of the stuff that makes ADV and Orange Crush great!
    #9
  10. gefr

    gefr Life is a trip

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    Here Loctite 648 is applied at the 6 bolts and the flange that mates with the flyweel.
    In the engine repair manual Loctite 243 is applied on the flyweel bolts, but a Woodruf key is used, so no Loctite is nessecary on the cranckshaft.
    Cheers.
    #10
  11. armourbl

    armourbl Adventure Life

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    Was wonder about this from one of your other posts on the topic. Do you think starting the bike while in gear leads to pre-mature wear on this part?

    Great write up BTW. Thanks for taking the time to do it.

    ben
    #11
  12. gefr

    gefr Life is a trip

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    It would give the sprag a hard time to turn the geartrain up to the clutch. These clutches are always having some drag.
    Cheers.
    #12
  13. keener

    keener Speed changes you.

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    Just updated the first post.

    Please take a look and let me know if there is anything wrong before it goes on the HOW.
    #13
  14. Hotbrakes

    Hotbrakes Adventurer

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    Wonderful write up, can't believe I found the solution so quickly. My SD has been down all winter due to this and I couldn't figure out why. Think I'll have the dealer fix it though, I don't have the time to mess with all the special tool stuff. But I'll be sure to show them this thread!
    #14
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  15. keener

    keener Speed changes you.

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    :)
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  16. gefr

    gefr Life is a trip

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    Special tools?
    You only need the 2 special bolts and some Loctite 648. Time you will need:1drink
    Cheers.
    #16
  17. keener

    keener Speed changes you.

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    The special tools are just two screws. Nothing special.
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  18. Powerbandy

    Powerbandy Just got here

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    Great write up on this job, gave me the confidence to have a go at mine :clap

    The only bit i was worried about was undoing the rotor bolt as i don'y have a impact driver. I found an old 7/8"s Whitworth spanner that fitted the flats on the rotor hub. with the spanner braced on a length of 4" fencepost and a 2 foot power bar on the allen socket it came out sweetly, no bother at all.
    The distance across the flats is 35mm, so i guess pretty much any open ended spanner just above that would be worth a go.
    [​IMG]
    Thanks again,
    Andy
    #18
  19. Chuckracer

    Chuckracer Jerkus Maximus

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    Oh good...subscribed so I can find it later. This is something I need to do this winter, I'm thinking.
    #19
  20. Somewhere Far Beyond

    Somewhere Far Beyond The Narrator

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    I had to do this job right after I bought my 06 950. Pretty fun project. If my 640 Adventure weren't shredded on the bench fixing the rocker cover leak (which turned into water pump rebuild for the hell of it and...other things. :lol3 ) I'd do it just to do it and make sure it's done.


    I love wrenching on my bikes. :wink:
    #20