Gearbox oil getting into engine oil

[super_rat]

2016 350 RR, 63 hrs. Any ideas how this could happen? Gearbox oil flows into engine oil, which due to over full condition is then blown into the airbox, then onto the ground. Gearbox and engine both filled with 750 ml of fluid before ride. After a short ride engine oil level was up to the top of the filler. Later 250 ml was drained from gearbox, 1100 ml was drained from engine. "Missing" 150 ml drained from airbox onto the ground.

Thanks

[Noppy]

I had exactly the same problem. Also exactly the same volumes as you drained from both sides. We were both very lucky, detecting it early!

It is caused by a leaky seal, seperating engine and tranny, located behind the clutch basket. Pretty easy to replace, two hours work plus one gasket. My bike was under warranty, so repaired without any costs. Good luck with claiming!

[super_rat]

Hmm.... it looks like gearbox oil is on both sides of the clutch so I don't see how a clutch seal could be the problem. Plus I don't see any seals behind the clutch on the engine parts diagrams.

It looks like the only seals that would separate gearbox and engine oil are the right crank seal. Maybe a balancer seal, I can't tell from the diagrams if the balancer bearings run in engine or gearbox oil.

[Noppy]

I didn't ask, but assumed it was the crank case seal, as he told me he had to dive deep into the engine.

[super_rat]

Ended up being right balancer shaft, seal, and bearing. Seal was leaking gearbox oil in CC and winding noise was the bearing. Had to replace all three. No idea what would cause relatively obscure and I assume non-stressed parts to fail.

[Noppy]

Nice that you know now! But funny that one assumess that the CC should build up pressure and not the gearbox?

But anyways, the opposite is better, I presume?