Hi Guy's
Having trouble with my 21 Racebike. It's sucking gearbox oil into the bottom Cylinder. Any ideas as to where the cylinder will be sucking the oil from. Its just had a new crank fitted along with gaskets
Etc.
It's a dry clutch 28 bottom end.
Cheers
Anthony

I've not had this problem myself (yet) but i've just put my crankcases back together and i had a look at the internal castings of the crank case halves to try to get my head around how the oil pump gets 2T into the oil feed holes of the crank main bearings. I also had a look to see if there was a way for gearbox oil to get into the crankcase somehow if a seal failed. I just ended up confusing myself really...

It might be getting through the 2T galleries from inside the clutch housing - i'm not sure which seals are responsible for preventing this though. Those two little rubber O-rings that go behind the oil pump drive gear are the only ones i can think of.

Another unlikely possibility is that gearbox oil is getting pulled past the clutch side crank seal when there is negative pressure in the crankcase on a compression/exhaust stroke.

You at Manfeild this weekend mate?
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After years of moaning about immigrants now i am one...

Hey Hermit yeah I to thought it could be thru that side of the crank seal. Yeah i'll be at manfield on the NC30 trying to keep the kwaka's honest .
I'll be in garage 5 pop in if your coming for a looky.

Stay strong Ant!

Everything will come together for ya!

I can't give you any tips to your problem just some motivational words!

Cheers Glenn
I'll keep the faith see ya Saturday

It's possible a poor seal between the crank case halves can cause the cylinder to draw in transmission oil, but it's much more likely the crank seal was nicked or not quite seated correctly, and it's drawing from behind the primary gear.

If it was a poor seal between the case halves, it would probably be a bit more likely to effect both cylinders.
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Andy.
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Great Thanks for the reply Andy.

My 1988 NSR250MC18 R2J would appear to be doing the same thing(front cylinder). The bottom end has never been apart, so could this be caused by the seals degrading through age.
The engine still sounds as it should and there is no erratic idling or poor starting. The machine has been stood/ garaged for approx. 8 weeks and was fine the last time I rode it.
I was also wondering where the best place would be to buy all the neccessary seals and gaskets.

I just ordered my crank seals and stuff from Lings Honda

this thread will also help if you are buying said parts....

http://www.nsr250.net/forums/viewtopic.php?t=8888
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CBR400 - track
MC21R - sold
MC21SP - sold

Thanks for the prompt reply, I will give them a try.