Crankcase breather hose

[Bob_Roller]

Here's the page from RealOEM .

The hose is item # 10 .

Like I said, the illustration looks nothing like the part !!

http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=11_1712&hg=11&fg=10

Here's a link to the Motobins page .

http://www.motobins.co.uk/displayfinal.php?q=11430&go=GO

[Rob Valdez 79 R65]

Here are a couple of home-made catch-tank solutions.  

This one is fairly typical, although I've never seen one so open to the elements:



This one is VERY clever!  Notice the large tube coming out of the starter cover, going down to the frame rail, where it connects with a rectangular box with a vent:



Photos courtesy of the German airhead forum, http://2-ventiler.de/
If you don't read German, good luck navigating their photo gallery!  I just happened to stumble across these in their random pictures that show up on the left side of the gallery pages.

[larstorders]

Avoid oil seepage from the left hand carburetor by simply directing the crankcase breather pipe into the right carb ONLY.
 No kidding it's works for me (on a 1982 light flywheel a 1981 R65). I did  replace the pipe in the airbox with one the same diameter as that which leads from the breather valve to feed into the right carb ( reducing any risk of increased back pressure). Good luck

[Rob Valdez 79 R65]

Avoid oil seepage from the left hand carburetor by simply directing the crankcase breather pipe into the right carb ONLY.
 No kidding it's works for me (on a 1982 light flywheel a 1981 R65). I did  replace the pipe in the airbox with one the same diameter as that which leads from the breather valve to feed into the right carb ( reducing any risk of increased back pressure). Good luck

Huckys (and others) sells the OEM tube for the earlier bikes that did, indeed, feed only to the right carb.



 11 15 1 338 215  $10 USD

http://www.bmwhucky.com/007511.html

Half-way down the page.

[steven m]

I just want to understand this, since after reading this post, and finding oil on the toe of my left boot after riding, I was surprised to find oil on the bottom of the horn from the air cleaner to my left carb.  Is the point that BMW designed a bike that fills up the airbox with oil that migrates to the left carb horn, or is this an issue with a cracked breather hose?  As far as not filling up the crankcase of an air/oil cooled engine more than halfway to prevent this, that sounds more than a little odd.  Is the California exhaust air injection is causing a low pressure situation in the air box that is drawing oil up as vapor which then condenses in the airbox and runs down to the carb?  If that's the case, then all bikes with that blocked off shouldn't have this issue. right?  Don't the later R65's have a reed valve crankcase breather?  That could add to this issue as the oil vapor does not have the opportunity to condense and return to the engine.  I ran a couple of long clear hoses from the breathers of a hot rod Honda 750  to the tail of the bike, GP style, which gave enough length for the pulsing engine pressure to dissipate without any oil gathering or leaking.  Wouldn't a long tube to the back of the bike, with the breather valve removed, allow the engine to vent properly?
Sorry for the length of this post but I'm curious to get to the bottom of the issue.  And keep my bike and boots clean!
Steve    

[Barry]

As far as not filling up the crankcase of an air/oil cooled engine more than halfway to prevent this, that sounds more than a little odd.

The idea is that it increases crankcase volume which will be less pressurised as a result and the breather valve then gets an easier time. All engines have breathers and all vent a little oil but you have to bear in mind that an airhead is not like a four where two pistons are going up when the other two are coming down. Both going down together in a boxer is much more of a challenge for the breather especially if there is any piston blow by or the rear crank seal is leaking air in. The breather valve is actually intended to pump down the crankcase to a partial vacuum to limit pumping losses and if there was no blow by at all it would not vent oil vapour ... it's not a perfect world though. I like Bob's suggestion about giving the vapour something to condense on and will try it sometime.

The breather tubes should be centred in the carb inlet tubes on both sides, they shouldn't touch the sides the idea being that the oil passes through the carbs as a vapour but we all know it can condense in the tubes and leak on your boot especially in cold weather. I too would love to know why the left side is favoured with the oil even without use of the side stand. Some say you should rotate the tube clip so that the screw is on the top and then the oil will not leak from the joint.

[Bob_Roller]

There are two different methods on how the vent tubes get to the rubber air horns .

One is a plastic insert into the throat of the air horn where the outlet is centered in the horn the vent hose goes over the end of the plastic insert as it protrudes from the air horn .

The other, which I have on my '81, has the rubber vent tubes that snap into the air horn, without any insert in the air horn .

Here's a page from RealOEM .

http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=11_1713&hg=11&fg=10



The plastic insert, what they call an extension, item # 17, was never installed on my bike .

[steven m]

I'm aware of the function of a crankcase breather, especially on a boxer engine or big twin.  Without a proper breather they would blow every seal and pump oil past the rings.  Triumphs have timed crankcase vents for just this reason.  Our airheads get more than half of their cooling from oil, and reducing the amount of oil is just not a good idea because it doesn't address the issue.  My bike is an 83 model year built 10/82 so I'm not sure which breather hose set-up it has, but both of them look like siphons to me.  I'll have to go and take a look.  If the breather on our bikes isn't valved at all, then replacing the hose that comes off the breather with a coiled line would effectively solve the problem by giving the length needed for the engine to vent and then allow the condensed oil to drain back into the block without any obstruction.  Like a hillbilly still.  Excess vapor can still go to the carbs without the tubes becoming oil tanks.  Or put a piece of coarse copper scrubbing pad like everyone else!

If I figure it out I'll post some photos.

Thanks for the input.
Steve

[Barry]

Our airheads get more than half of their cooling from oil, and reducing the amount of oil is just not a good idea because it doesn't address the issue.

I understand where you are coming from here and you are right in principal. No one is saying we a have a perfect breather system so the reality is that most airhead owner run with the oil level half way between the max and min marks on the dipstick. In fact if you read the owner's manual carefully I think it says don't add oil until it gets to the min mark as if they were aware of the problem. Those who fit deep sumps will often say that it is an opportunity to increase crankcase volume rather than increase oil volume.

As for needing oil volume to cool certainly on an R100 or any airhead running in very arduous conditions. My own concern most of the time is getting the oil hot enough never having recorded a sump temperature higher than 80 - 90 deg C. If an airhead was running with hot oil all the time I think it would be more likely to pass through the carbs as vapour rather than condense so there would be less of a problem anyway.

[steven m]

I think we are in agreement.  My bike runs nice and cool on open roads, the faster the better, even on a hot day. It's when we shut off that the oil condenses and heads not back into the block but down the breather tubes towards the carbs.  So the oil on my boots isn't from that days ride but from the last one.  Time to clean out those tubes.  

My BMW car manual also suggests not adding oil until it drops to the minimum level but I think that is to keep owners from just dumping in a quart and over filling!