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'Muddy' gearbox oil


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Hello, I was just visually checking my bike through the 'porthole' this morning and noticed that the oil was a little cloudy. On draining, the oil was a little milky coffee coloured. I've seen quite a few examples of head gasket leaks and the oil was nowhere near as milky as one of those. There were also some small residues which I initially thought might be rubber from a worn-out seal - however, on examination, they appeared to be mud. I've had a trawl through a number of threads and the most common diagnosis for water in the oil seems to be a worn impeller shaft however, this would not explain the mud.

I'm guessing that the most probable cause is overuse or poor aiming of a pressure hose. Would I be correct in this? Or any other thoughts? 


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Coolant still full. Oil been in approx one month - around 20 hours, I would guess.

Also - have checked carb, air cleaner, filter etc. Anywhere that mud/dirt could have got in. Nothing out of place there.

Edited by oldgit
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On 08/04/2017 at 10:17 AM, guys said:

Is the breather tube still properly connected and routed as the clear tube in this picture, that's connected to the gearbox in front of the sprocket?


Clear tube still connected. No sign of the purple tube - but I guess that's from the Keihin carb and mine's fitted with a Dellorto. I'll have a much closer look tomorrow once the bike's cleaned and dried. Apart from that - done four or five hours over the weekend and new oil is still crystal clear. Hoping it's a one-off but checking out the water pump.

Thanks again.

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