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Breva 750 Crankcase Breather

M0T0Geezer

M0T0Geezer

Cruisin' Guzzisti
Joined
Mar 3, 2013
Messages
131
Location
Sun City West, AZ
I have a 2004 Breva 750. Starting to get oil seepage/weepage along the engine to bell housing joint. More oil coming out the weep hold in the bottom of the bell housing. Beginning to think this is [yet] another symptom of engine oil overfill (but I carefully try to avoid that). I think there is pressure building up in the engine (blow-by?) that is forcing the oil out. Shown below is after about an hour's run:
20151026_Bell_Housing-s.jpg


Diagrams from the Parts and Shop Manuals do not directly map how blow-by pressure is getting dissipated. Only the oil vapor tubes from each valve cover into the Air Box are shown as possible vents. How does blow-by pressure get into the valve covers? Up the pushrod galleys?

I verified that the non-return valve is working properly (i.e., only allowing flow of air and oil from the Air Box and back to the crankcase oil pool). This could only happen when there is greater vacuum (negative pressure) in the crankcase than the vacuum present in the Air Box. When would/could there ever be more vacuum in the crankcase than in the Air Box? How (and where) is positive pressure in the crankcase relieved?

Basically, the Crankcase Breather seems to only be able to suck - never blow. Anyone here have intimate knowledge of the actual oil pathways - vapor and liquid - in the '04 Breva 750 motor?

Thanks for sharing your info - 'Geezer

CrankcaseBreather_02


CrankcaseBreather_01
 
M0T0Geezer said:
I have a 2004 Breva 750. Starting to get oil seepage/weepage along the engine to bell housing joint. More oil coming out the weep hold in the bottom of the bell housing.
Click to expand...
Is it definitely engine oil or trans oil? If the engine has never been out, an 11+ year old motor is likely just having the rear main seal go. Pretty decent actually as to time. It's a big job to do, and best to do the clutch while you're in there (sorry to say). Keep us posted.
 
It is definitely engine oil seeping thru the joint and dripping out the weep hole under the bell housing. Clutch is acting fine (so far) so I guess I don't need do do anything until it starts slipping.

Agreed - the Breva 750 engine is running marvelously well at 11 years old and 42,000 miles. The ECU reflash you did for me 30,000+ miles ago was the best $$$ I've ever spent.
 
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