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Crankcase Vent

7K views 15 replies 9 participants last post by  BP6666VR 
#1 ·
I've searched and read related threads posted here in the past few years. What I've yet to determine is where exactly the vent tube returns to the airbox. Do the vapors from the crankcase get filtered by the air filter, or do they enter past the air filter. My hose came disconnected at the elbow behind the rear cylinder and produced an oily vapor film in the area. I reconnected the tube and cleaned up the oily residue, but wondering if I sucked in unfiltered air through the open end of the vent tube. Thanks,
 
#2 ·
I just had all that torn apart not two days ago, but failed to notice the routing of the hose.

Logically (ha!) the crankcase should vent OUTBOARD of the air filter, which means you should be just fine.
 
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#3 ·
The vent enters the airbox post filter, so when the tube comes off, it will allow unfiltered air to enter. It has to be post filter to allow clean air in to the crankcase with negative pressure.
 
#4 ·
Thanks for clarifying.
 
#5 ·
I guess that is why people have dirty throttle bodies ...

Andre
@
TaPaTaLk
 
#6 ·
Bingo! One of the best things you can do (especially on an older steel frame) is cap where the tube attaches to the airbox and install a separate filter on the crankcase breather. Oil in the intake track can gum up the throttle bodies and intake tracts/valves.
 
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#8 ·
Yeah, I was thinking about this yesterday, and my answer was 100% wrong. I actually couldn't think of a single automotive application that uses a PCV line outboard of the filter.

I dunno what the hell is wrong with me sometimes.

:crzy:
 
#14 ·
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#10 ·
CC all models and vision have the vent tube run to a nipple on frame towards the back of it all most straight up from the gear sensor unit. So if anything you would get fumes into the throttle body. Not oil.

99 to 07 the blow by tube goes to the air filter housing. That's why you need to clean them once a year
 
#11 ·
steel frames

my 13 hammer had the tube going to the air-box i removed for the Ness aka S+S style without the bling or $$ filter, as noted a drip or two which hits a piece of cardboard under it after a ride. oil mist of any kind in the intake + can contribute to pinging as well! i quickly rerouted the problematic venting my traded hardly had after learning by reading, forums are a great source of info!!!
 
#13 ·
Lab Analysis

Received the results from the lab work done on my oil sample. Blackstone Labs gives me a clean bill of health. No abnormal wear numbers due to abrasive dirt contamination by ingesting unfiltered air through the intake or through the crankcase vent.

With 1600 miles on new oil and filter; after discovering the vent tube detached I drained and changed the oil and filter - and collected the three ounce sample for lab analysis.

Probably a bit obsessive, but just for peace of mind I changed O & F once again 250 miles later - in theory to aid in purging any residual crap from the internals.

My season is done. The scoot, with another 250 miles on fresh oil, is perched on a scissor jack till April 1st.
 
#15 ·
VJ, I would have to disagree. I just got finished changing out my upper frame from VicBaggers to stock. I layed the VB upper frame on the garage floor upright. I was surprised a couple days later when I noticed a small puddle of oil under the frame piece. I barely have run or ridden this bike as it is my trike conversion I've been working on. Maybe a mile or mile and a half with some intermittent running in the garage. I would say there was maybe two to three table spoons of oil that I wiped up.
 
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