Help me find TDC on a 950 Adventure

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by Ewan McBoorman, Mar 12, 2018.

  1. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Hey everyone, hoping you all can help me. My bike was in at the local shop because it hasn't run great since I've owned it. They did a leakdown test and said it was leaking a little bit. They suggested a valve check among other things. I paid for some of the work, but figured I should learn to do the valve check, so I read up on the HOW.

    The valve clearances all seem within spec, but I was having trouble finding TDC. Maybe I'm just missing something, but it seems out of whack.

    On the rear cylinder, when I rotate it through, it seems to come to TDC when the tooth with the X is about 1 tooth above the cylinder head surface. When it is 1 tooth above, I can feel the piston at TDC and the locking screw will go into place. When the X tooth is level with the cylinder head surface, the locking screw will not go into place. Also, I can barely get the X tooth to line up because it's on the verge of clicking over (not sure what does that).

    On the front cylinder, again based on using a screwdriver in the sparkplug hole and with the locking screw, it feels like it reaches TDC earlier than when the circle lines up with the cylinder head surface.

    I made these extremely amateur videos to try to show the issues. Sorry, it's hard to hold my phone, crank the engine, and hold a screwdriver.





    Thanks for all your help.
    #1
  2. geometrician

    geometrician let's keep going...

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    The TDC crank locking tool is the definitive way to find TDC on KTM's (they use them in pretty much all their four strokes). Using a chopstick (easier on piston crowns &spark plug threads than a screwdriver) you can determine where TDC is to verify the crank drilling is in the correct location on the crankwheel (I have yet to see a KTM TDC crank depression off). Once you have verified TDC, use a fine marker to scribe a line all the way around the chopstick so you can use it as a reference next time. I have several of them, marked for the different bikes I own/work on.

    The cam marks/teeth are usually a little bit "off" from perfect alignment with the top of the cylinder head casting. Given the number of crank sprocket teeth, the upper cam chain (intermediate) sprocket teeth and the cam sprockets themselves, there is no way to "fine tune" 950 cams without serious modification (there is an Orange Crush thread on this someplace) moving the cams one tooth produces a huge cam timing change, and as such, you'll have to live with the small discrepencies you are finding now.

    One potential issue is the lack of cam tensioner oil pressure (our tensioners use oil pressure from the running engine to completely extend the tensioner) allowing slack in the chain to appear as misaligned cams. For this reason it is best to always rotate the engine in the running direction only so the slack is pulled from the exhaust side and you get consistent cam placement.- moving the engine back and forth even a small amount can throw this off.

    Q: do you have clearance on all of your valves? Simply rotating the cam buckets by hand (finger!) when that cylinder is at TDC will let you know the valve aren't operating with zero/negative (valves held open off seat) clearance. Feeler gauages can be used; but a closed valve is a closed valve even if the clearance is out of specification.

    As for leakdown, with the TDC in place you can inject air (100psi typical) yourself through an adaptor hose (Harbor Freight compression & leakdown testers will work) and listen for air coming from:
    (1) exhaust/muffler outlet - exahust valve/seats loss of sealing
    (2) intake manifold - intake valve " " "
    (3) crank breather hose - piston rings/cylinder loss of sealing

    You can use the leakdown tester ($40 on sale) to arrive at exact figures. You should hear no noise through any of these three sources- if you do, then you have an issue.

    If you are this deep in your engine there isn't much you can't do yourself (adjusting your valve clearance yourself)
    #2
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  3. fast4d

    fast4d Long timer

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    another trick to be sure it's on the compression stroke make sure air is being pushed out the spark plug hole. I've see a guy use a fitting with a balloon to confirm but you can just use your finger to feel the pressure.

    using a stick with a sharp end in the TDC holder hole would help you find the indent. I always have trouble feeling it with the holder bolt.
    #3
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  4. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Wow, thank you for such an in depth answer! I will try to answer all your questions. I have only been cranking the engine CCW in the direction of normal travel as advised in several of the valve check write ups. I had thought about cam chain stretch or it just being off slightly, but it seems to be off exactly a whole tooth. I did verify that I was on the compression stroke using a screwdriver to feel the piston come up, but I do like the chopstick idea a lot better. Time to order some takeout!

    I will check out harbor freight for a leakdown tester, I would like to run that test again while I'm in there.

    I guess my next steps are to crank back through the cycles again and verify with the chopstick/locking tool hole that I'm at TDC. If the cams are exactly 1 tooth off, then I unbolt them from there and re-align them with the correct teeth. I also checked that they are K600 cams, not superduke K611's. I'm just not sure who could've put them a whole tooth off...

    Oh, and my valve clearances were all within spec:
    Exhausts were .254, .254, .254, and .279mm
    Intakes were .127mm all the way around
    #4
  5. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Yes, I was for sure feeling the air being pushed out. I started with some rags in the spark plug holes, and they shot out the first time rotating through. From then on, I could hear it as I was trying to also feel the piston coming up.
    #5
  6. fast4d

    fast4d Long timer

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    the HF leakdown did not work for me the thread on the adapter either didn't fit or thread was badly machined. I didn't want to strip the threads.

    buy the one off amazon.
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  7. geometrician

    geometrician let's keep going...

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    You can watch the intake lobes press the valves open, then as you continue to rotate the engine (in correct direction!) you will always be at TDC of compression stroke.

    Glad to be of help. If you do have leakdown, 3% is considered by many to be an acceptable amount... some losses are so high you can hear the air easily... I turn all radios/fans/etc off when using the ol' ear-test (once you find that it is leaking you can use the gauges to determine amount.

    FWIW I use a 4mm ball-end allen tool to help find the TDC "divet" in the crank; then I use the factory TDC tool and move the crank ever so slowly back and forth until the taper of the tool fits snugly in the crank (and it locks up solid, always a good feel; other bikes can rotate their engines with air pressure at TDC and no locking tool, a rare but scary expereince)

    Enjoy your take out!
    #7
  8. geometrician

    geometrician let's keep going...

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    Yeah I have owned/used a couple of HF compression/leakdown testers and the thread sizes on the adaptor hoses have varied; I currently use one of the compression hoses on the leakdown tester on the 10mm spark plug holes. Seems they were rare a few years ago now they are found in all sorts of engines
    #8
  9. nk14zp

    nk14zp Long timer

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    I think you might have found why it's not running right.
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  10. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Yeah, I went in thinking it was a mis-adjusted valve. I haven't had the bike that long, but it took me around Lake Superior last fall. If it's really off a tooth, I'm surprised it ran at all.
    #10
  11. kvango

    kvango Been here awhile

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    Pulling cam reminder: You probably know this, but make sure there is no pressure on the cams when pulling off the bridge. TDC each piston is fine. Torque/loosen in stages, note bolt sizes and different torque specs. - definitely don't want to crack a bridge (not sold separately).
    Kevin
    #11
  12. DirtyADV

    DirtyADV Long timer

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    I would NOT use a chopstick or anything that can break easily to push it and feel the place to lock the crank. If it slips into place and you move it some more and break it.

    A screwdriver or allen key would be better if you ask me. Or it can be seen if you have a flashlight and decent eyes.

    Nice with an extra hand turning engine while looking for the opening in the crank.

    /Johan
    #12
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  13. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Just to let everyone know, TDC has been found! And it's right where it should be... Apparently I was being too cautious about feeling for it with the screwdriver. I cranked the engine through many cycles, and when it would get close to the marks on the cams, I would let the rounded end of the screwdriver ride along the crank. I found the divots in the crank where the locking tool goes, and I can lock the engine. The KTM locking bolt still doesn't go all the way in so it's flush or recessed like a lot of the write-ups show, but it seems to all line up correctly.

    My brother is bringing his leak down tester on Sunday and I have the adapter from Amazon, so I should be able to get my own reading and see if there are any leaks anywhere.

    Thanks for everyone's help!
    #13
  14. geometrician

    geometrician let's keep going...

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    not all the crank locking tools fit flush with the cases (this tool is used on scores of KTM 4-strokes).

    I use a 4mm ball-end allen tool to help locate the approximate hole and then use the tool to get the exact TDC alignment after that. Using a breaker bar (instead of a ratchet) to turn the engine allows you to line the crank up (instead of having the cone/taper fit of the tool/crank do it) as you tighten the tool.

    @Ewan McBoorman hope she comes to life and gives you many miles of enjoyment!

    My golly never thought a chopstick would generate so much discussion... as a former full-time wrench and owner of my own shop in San Francisco I can tell you I've done literally hundreds and hundreds of TDC checks with the same 'stick without a single mishap or even putting a mark on it. YMMV
    #14
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  15. Ewan McBoorman

    Ewan McBoorman The voice of reason is annoying

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    Thanks!

    Looking back at the comments, I think there is just some confusion on where you suggested to put the chopstick. I see you said to put it in the spark plug hole to feel the piston. It looks like DirtyADV thinks you meant to put it in the locking hole to feel the crank divot and he was rightly concerned about that if that's what had actually been suggested. Just a bit of misunderstanding I think.

    Thanks again for the help.
    #15
  16. DirtyADV

    DirtyADV Long timer

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    Maybe some misunderstanding. Sorry about that.

    And if looking for piston TDC I agree with something wooden is suitable, a little caution on other engine with the spark plug at an angle here the same concern about breaking anything inside cylinder.

    /Johan
    #16
  17. Motomedic

    Motomedic Over-caffeinated Raconteur

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    If you're really worried about breaking the chopstick off in the hole, use a zip tie....:becca
    #17