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Thread: Crankcase breather mod - What did I do wrong??

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    Crankcase breather mod - What did I do wrong??

    hmmm, so I read up plenty about doing this. I don't need fancy CNC catch cans and whatnot. First, it runs fine. I'm getting oil blow by/mist on various parts. Pretty minor, accumulates with time - not instant or anything. The filter is mounted in the upright position versus sideways/upside down which would promote oil pooling.

    Is the angle of the tubing too much? I saw numerous other set ups where it looked almost identical and no talk of this issue.
    Do I need to relocate the filter? Run a leaner meaner set up that basically goes straight down from the front of the engine instead a rear discharge?
    I took it all apart and there's some of that milky oil residue. Nothing poured out or anything obscene.

    Thoughts?
    oil.jpg
    DSCN1333.jpg
    DSCN1332.jpg
    DSCN1334.jpg

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    Senior Member Cooter's Avatar
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    Normal.

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    Senior Member Barrett's Avatar
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    Aesthetically, it's amateurish in appearance and a tad more complex than necessary. Consider a simple 3/8" standard line from the base-plate "T" to right rear foot guard/master cylinder area and terminating with simple 3/8" plug-in filter.
    Any concern regarding type and amount of breather "gunk" can accurately be addressed and assessed with simple compression and leak-down test. Accurately reveals internal engine health if performed correctly.

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    Are there not reed valves on the crank breathers of these bikes to prevent something getting pulled back up the line? What's the point of the filter? I feel like the line could be run down and just open vent to atmosphere. Just curious what I'm missing here and why I keep seeing these seemingly over designed systems.

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    Well, while I was reading up about various versions of this, I read somewhere about vacuum or something potentially being an issue. As long as you let air in, oil goo will move along.
    Initially I just wanted a much more basic set up but xxx and his buddy xxx swore you needed a filter. I def wanted it rear exit cuz I don't need that discharging directly in front of me, getting that schmoo on my and my bike.

    I didn't realize the filter would just become a vent to atmosphere kinda situation. NO ONE addressed this in any post that I had referenced to both here and at badweatherbikers.

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    Senior Member Barrett's Avatar
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    Quote Originally Posted by Thunderhead View Post
    Well, while I was reading up about various versions of this, I read somewhere about vacuum or something potentially being an issue. As long as you let air in, oil goo will move along.
    Initially I just wanted a much more basic set up but xxx and his buddy xxx swore you needed a filter. I def wanted it rear exit cuz I don't need that discharging directly in front of me, getting that schmoo on my and my bike.

    I didn't realize the filter would just become a vent to atmosphere kinda situation. NO ONE addressed this in any post that I had referenced to both here and at badweatherbikers.
    NO ONE addressed this in any post that I had referenced to both here and at badweatherbikers.

    That's because NO ONE ever asked me about it.


    XB breather system very similar to XL and XR1200 systems. As follows:

    The crankcase assembly is shrink-wrapped around the crankshaft and con rod big end and the 2 large pistons generate a substantial amount of both pressure and vacuum.

    The venting system is "timed" to coincide with accumulated pressure, which is vented into the stock OEM airbox assembly outboard of the air filter and intake ramp and is vacuum assisted by the normal engine operation to re-enter the engine on each intake stroke.

    The pressure relief valve or sometimes called positive crank vent valve....is located one atop each rocker box cover...sealed to same via a rubber grommet. It is a "pedal" design which allows pressurized air or "chuffing air" to vent to atmosphere, but does not allow air to re-enter the engine during the intake stroke of each cylinder.

    The entire system is designed to both relieve internal pressures and meet EPA cycle standards.

    A breather "reroute mod" done to a healthy motor can have the venting terminal line exit anywhere that is slightly below the level of the throttle body. Must be below that level as a reroute has now lost the vacuum assist that the airbox provides.

    I terminate the reroute vent line with a clean, simple economical filter for both appearance and to keep dirt and insects out of the vent line. Not absolutely necessary but aethetically pleasing, IMO. Puke tanks...overflow catch devices...drain valves...all ridiculous frivolous bull****.

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    Senior Member 34nineteen's Avatar
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    Damn... handsome and smart. Who knew?

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    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by Pitcherman View Post
    Are there not reed valves on the crank breathers of these bikes to prevent something getting pulled back up the line? What's the point of the filter? I feel like the line could be run down and just open vent to atmosphere. Just curious what I'm missing here and why I keep seeing these seemingly over designed systems.
    There are reed valves inside the engine case, but I believe they were installed to help with the cylinder heads draining oil (dont quote me on that). There are PCV valves on top of the valve covers to help with crankcase breathing, which basically sort of work like a reed valve. I think there are pics on here or badweb of them cut open to show the umbrella valve and filter built into the PCV valve.


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    https://www.twinmotorcycles.nl/websh...catch%20can&a=


    If you really like spending money, here is a link to CoOters Only Fans page.
    Last edited by 34nineteen; 09-13-2021 at 10:50 PM. Reason: link removed by moderator

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    Senior Member Cooter's Avatar
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    If you feel you don't want a tiny amount of oil vapor to be run back through the engine simply Tee-ing the breathers together at the valve covers and run a small line down to the swing arm pivot is all that needs to happen. Also called a draft tube or road draft tube.
    You could put a dip or loop in the line in order for the vapors to eventually coalesce and act as a filter or bug trap but really not needed.
    You could also add a little filter at the end to soak up some vapor and stop the bugs with no bad effects as well.

    This super simple 'mod' has been done and OVER done elevenmillionty times. The rule is: if your engine is puking so much blow-by you are getting liquid out of that tube every ride, park the bike and order a re-build kit.

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    Sounds like I'm either gonna relocate the filter a little further away per Barrett or just delete it. I went with this set up cuz it was relatively simple (no ridiculous CNC, brackets, or similar silliness) and I wanted it to discharge towards the back, no front dangling. That being said, I have had surprisingly little blow by/oil collection/schmoo when I pop the end cap - aside from the stuff in the pics. That's after around 3,000 miles.

    I just saw numerous set ups with the in line filter and was a little surprised cuz no one mentioned anything about this. Maybe its a case of the here's a mod, I've done it, everyone else has done it but nobody really follows up on it many miles later. So here ya go, here's a follow up.



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