KTM 530 exc gearbox breather clogged up

Since I haven’t found any information at all regarding my problem with the gearbox breather hose, I’ll post the solution in english also, for all of you guys who don’t speak swedish.

The problem began with oil leaking from the drive shaft on the bike, a 2009 KTM 530 exc Sixdays. Since this is a quite common problem I simply replaced the seal and bushings, which of course did not fix the problem. The oil was leaking kind of sporadically, more often after short rides than after long rides, and it didn’t leak much..

So, this summer I took the motor apart, replacing the crank shaft seal on the right side (which is usually leaking), replaced the oil pump seals, housings and shaft and replaced the piston rings. I also put new seals everywhere it was leaking. Yesterday when I went for a test ride after rebuilding the motor, it still leaked.. 🙁

When I stopped I could hear a kind of gurgling sound from the filler cap on the gear box, and as I opened it it sounded like opening a soda can. There was a lot of preassure inside, which should be vented out through the breather hose! When I tried to apply preassure to the breather it was sealed. No matter how hard I tried to blow into the hose, I couldn’t push any air through. After some research I opened the cluch cover on the motor and removed the cluth and kick starter. If you put your bike on the side like this you won’t even have to drain the motor oil:

Bike on sideAfter some investigation I found out that the breather is routed through the shaft of the gear connecting the kick starter, here:

WhereItGoesAnd what was wrong on my bike was the gear itself. The brass bushing inside the gear wasn’t correctly aligned with the gear:

Misaligned holesThe holes in the gear and the bushing are supposed to be aligned, to let the air in and out of the breather hose. For some odd reason my bushing was misaligned and no air could escape the gear box, which is why it started building preassure inside as the motor got warm and the air and oil trapped inside expanded.

The solution for this is pressing the bushing out of the gear, realigning them correctly and – using some kind of loctite – pressing it back togeather again.



ResultRight now I’m letting the loctite cure for a bit, then I’m going to re-assemble the motor and go for a test ride. Hopefully most of the oil stays INSIDE the motor this time. 😉


The fix worked, did a quick ride of about 10km today and not a single droplet of oil was underneath the motor when I got back. First time since I got the bike that that’s happened!




4 svar på ”KTM 530 exc gearbox breather clogged up

  1. hi, thanks for posting. i bought a ktm 530 exc-r 2 weeks ago, and its leaking a small amount of oil from the counter shaft seal, will replace asap when i do the chain and sprockets. previous owner said it drinks some oil, which it appears to, is yours at all like this? also cam chain is quite noisy, not worryingly, but noisy all the same, yours like this at all?
    thanks rick

    • Hi Rick,
      My KTM was leaking a lot from the countershaft seal until I fixed the clogged breather problem.. I replaced the seal like three times before I found the problem, unfortunately the previous owner had managed to damage the shaft while replacing the seal so it’s still leaking, but just a tiny bit..
      Mine doesn’t drink oil from what I’ve seen, maybe it’s time for a new piston and rings? Worn piston rings usually means that it burns oil.. do you have the service manual for the bike?
      The cam chain makes some noise even after replacing it with a brand new one.. KTM:s aren’t known for running smoothly, but they’re great fun to ride! 😉 Do you have the stock cam chain tensioner? That one is known to get stuck which may cause a seizure if you’re unlucky, so if you’ve got the stock one I’d recommend geting an aftermarket tensioner from dirttricks.com, made my bike quite a lot less noisy and it’s supposed to be much more reliable..

  2. marcus, thanks for the heads up about the aftermarket cam chain tensioner, will most likely get one. previous owner had said he’d recently had the top end rebuilt, so i don’t know about worn rings? however he didn’t say when, there was no service history (which is typical where i live, portugal) so can’t be sure when he had the rebuild, its drinking about 50-100ml’s ish on a 70km hard ride.
    am with you on ktm’s not the smoothest running bikes this is my 2nd (other one is a 640 adv, which seems to have its own set of problems/idiosyncrisis).
    got a bit of an overhaul to attend to on the 530 this w.e. so will see if the oil leak from the counter shaft stops when i replace the seal.
    i found a copy of the engine service manual online thanks.
    btw, can’t tell you how impressed i am with your rally build, that you made just so much stuff, it is freakin awesome. would you consider marketing it as a kit?
    thanks rick

    • 100ml every 70km sounds a bit much, I noticed that mine had consumed some oil (not 100s of ml though) after a 500+ km day of riding which I assume is more on the normal side.. Rebuilding the top end doesn’t necessarily mean replacing the piston rings so if you’re planning on an overhaul it’s easy enough to lift the head/cylinder and measure the piston ring gap. The tolerances are specified in the service manual and rings are cheap enough to replace. 😉

      I too had a 640 adventure before getting the 530, and as you say it’s got its own set of problems but over all a real nice bike to own.

      The breather is easy to check. The breather tube is connected to the engine in two places, in the gearbox and in the cylinder head. In between there’s a T and the third tube goes to the air box if I don’t remember it wrong.. Just disconnect the tube going to the gearbox from the T and try to blow air into it. Just use your mouth. Air should flow freely with little resistance when the oil filler cap is removed. When mine was busted I couldn’t even force air through using my 10 bar air compressor, and if that’s the case on yours (which it proably isn’t) you need to fix it.

      Thanks for the kind words. I really don’t have the time to start manufacturing stuff, but all the 3D-models and drawings are available for download if you want to make a kit yourself.. 🙂

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