Resolving motor oil migration | 2008 KTM 530 EXC with XC-4 motor

Finally resolved the oil migration issue on the 2008 KTM 530 EXC, the first year of the XC-4 motor that contained separate motor oil and gearbox oil compartments.

The bike’s factory breathers is a closed system connecting the crankcase from the valve cover, the gearbox, and the air intake after the filter. In other words, none of these systems vent to the outside.

On my bike, oil migration was happening out of the crank case breather, which is connected through the roof of the valve cover. Visible through clear breather tubes, there was oil in the tubes leading to both the intake and gearbox. No telling at what rate, but enough to require topping off the engine from half, as viewed through the sight glass; equivalent to a few ounces, after every rally of enduro hours.

idler gear with bushing removed for realignment

The kickstarter lever, on the right hand side of the bike, has an idler gear accessible under the clutch basket and located directly under the gearbox breather. It’s a solid, beautifully machined gear, but has a problem with oiling holes found to be misaligned with its bushing; how? Am not sure, but it can be corrected.

Upon opening up my case and indeed finding them of sync, started by extracting the bushing and pressing it back in with the correct oiling hole alignment.

idler gear

Used an appropriately sized socket to bushing diameter, then hammered on it to drive the ring out. Clocked the two pieces in synchronized oiling holes, then pressed them back together flush.

idler gear, oiling holes correctly aligned

Published by Manolo al Sol

Learning by adventure.. will curiosity kill the cat ?

10 thoughts on “Resolving motor oil migration | 2008 KTM 530 EXC with XC-4 motor

    1. Not a mod rather is a correction to factory ’08 XC-4 config. The crankcase oil in the closed system will instead enter the carb intake from manifold pressure. Only when the motor is off and cooling can i see oil thru thru the clear vent lines migrating toward the gearbox which is lower in the circuit. Seems my oil issue is back, and i suspect the idler gear and bushing have spun again. Will open up again soon, and if so plan to notch the two together with a center punch in a few places for an interference fit.


  1. Sorry to hear that your oil probelm is back. What I dont understand is:
    1- If the oiling holes are misalligned, wouldnt that block it off and not allow any oil coming in or out of the gerabox breather?
    2- You mentioned that you can see oil in the clear vent lines when the engine is off, (I assume that you have replaced the oil breather lines with clear so you can see, but why when the engine is off?

    Thanks for your support in this and look forward to fix this issue…. its driving me nuts!


    1. Good questions. Once my local weather dries out to get back on the horse, will revisit this issue as the oil consumption has not been out of control.
      Yes, swapped in clear lines for visibility and reverted back to closed breather circuits instead of open, which put oil all over the back tire.
      Btw just clocked over 350 hours and have no record of previous owner habits, yet valves are in spec and she rips all day in the desert or up the canyon on supermoto; just needs chain oil and topping off gearbox oil.
      Lastly, did you also see my other post about documenting use of OEM 2011 oiling parts?


  2. yes I did, thakns for the link. My concern is that my gearbox oil level is not affected, therefore I am inclined to belive it is not migrating… I have been losing engine oil, the whole sight glass, every ride of approx 50km… either on dirt or road. This has been consistent with before the rebuild and after…


    1. Is your breather circuit factory, which on an EXC (USA version) also T’s to the intake after the carb? That means the oil consumption is most likely getting consumed through the intake and combustion, and some argue it is intentional like how a 2-stroke fuel/oil mixture acts as a piston ring lubricant.
      My gearbox oil is consistency cleaner and over capacity when changing oil, which leads me to believe why KTM decided to try the split oiling compartments to put them on different schedules. I still change both oil and screens at the same time because it uses so little to begin with.
      Yes, going from top of sight glass to bottom is not much in actual oil capacity, but concerning for the XC-4 and its sub 1L total oil capacity. Next time you replace the clutch is a good opportunity to address the idler gear bushing.
      Also, have you addressed your water pump, which in 08 was known for having the outer seal to impeller installed backwards. If not addressed, then the seal between engine case and water pump cavity goes next and makes milk shake out of the engine oil coolant mix.
      Lastly, there is a final issue i have not personally tried to verify, and that is under the valve cover with one of the overhead cams. IIRC, and this is something you may want to independently search on sites like thumpertalk and advrider, a cam bearing directly under the breather vent comes out of alignment in its blind bore and causes a blockage preventing crank case venting, which then causes the forces oil via another route other than the breather circuit. It is a much more invasive fix requiring getting to the cams and this bearing.


  3. HI, yes breathers re factory, all other smog gear have been removed. Thats my thought too,.. I may vent it out to confirm.
    I havent heard this is an intentional 2-stroke alike reason but it seem like a lot of oil for lubing…
    I change both together as well and yes the g/box is always cleaner and at the right level. I check the g/box level everytime I top up the engine to confirm if migrating…. but migration doesnt seem to be my issue.
    Now… the water pump… no I havent and i did notice there was a slight leak of oil coming from the drain hole… do you have a guide on this?

    I have heard of the cam bearing now that you mentioned it,.. will need to research more..

    Have you played much with the carby and the JD jet kit?


    1. post on water pump seal service:

      Bike came with a JD jetting kit from previous owner. My simple sanity check with carb tuning is to ride Death Valley National Park, where altitude ranges from below sea level to above 8000′ at the top of Cerro Gordo. The bike starts and runs beautifully within the entire range, so have had zero reason to open it up despite excessive deceleration backfiring with a full Akrapovic exhaust when chopping the throttle on supermoto down the canyons, but i don’t mind it at all. If the bike sits over the winter or any length of time i do run the bowl dry as California gas will eventually clog idle jet.


  4. Sounds well sorted… I have just put the JD kit in and I am going through the process of fine tuning but so far so good. I have a hea p of problem with starting when I first got it, fixed it byreplacing the cam due to the decompression valve been 180deg out from factory. Then replaced the stator and has been great since.

    I ll do the water pump next and continue on my oiling saga.
    Thanks for all your help.


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