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Crankcase Breather Mod

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When I first got my kx450f I looked at the crankcase breather and thought "what were they thinking with this?" Sure enough, I looked online and found that people were concerned by the blowby coming off and others had even found dirt or water in their oil. Blowby happens when the machine is operated at high RPM and oil passes out as air is venting in and out of the bottom end. Toxic Moto Racing has developed a catch can and air filter that can be purchased for $124.99.  Today I made one similar to theirs with parts you can buy at any generic auto parts store for much less.

 

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3/8" generic crankcase breather filter

3/8" generic fuel filter

zip ties/hose clamps

*new 3/8" tubing, but you can cut the stock tubing if you want

 

This design should allow for the oil that splashes up through the tube to be caught in the fuel filter and be able to drain into the case again, keeping dirt out of the engine. I cannot say it will keep water out but it should help. When it is time to wash the bike the filter can be removed and capped like you would with your air box. To secure the filter to the bike I ran two zip tires through the radiator (not over any fins) and used those as an anchoring point to tie the fuel filter down with another zip tie. You could use anything as a catch canister, I like the fuel filter because it acts as an obstacle for the oil to pass around and if there happened to be a pool of oil in it the paper filter would keep it from sloshing up and through the air filter. The paper filter also serves as a secondary filter in case you happen to forget your air filter or anything happens to make it by. Just wanted to throw this idea on a forum for any of those guys looking for a cheap and easy solution to the blowby.

 

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Nice work and a great idea.  My KX is used a snow bike also and the concern there is getting water into the oil via this breather hose.  I wish there was a one-way valve similar to a gas cap vent valve that would allow the air to escape but not let water run back down the tube.  Using a one-way valve like this would necessitate some re-plumbing of the line so that any moisture trapped above the valve could have an escape route obviously.  I attempted something like this years ago on my old YZ426 but I could not find a valve with a low enough cracking pressure to make it work.

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Air compressors use water separators to separate the air and water and catches it in a bowl, they can be a bit heavy of a solution but you can use one of these later in the line to catch water and leave the fuel filter close to the breather inlet to catch the oil.

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So I ran into an issue with this design. The stock design utilizes the siphon effect so that when you lie the bike over the oil does not run out. Recently I tipped my bike over to the right past 90 degrees and left it there for a while as I laughed about my poor riding with my friends  :lol:  At the time I did not notice but oil had passed through the catch and now soaked the air filter so it quickly collected any grime in the air. Now I am working on rerouting a tube multiple ways to keep the catch tank, and an air filter without oil ever being able to reach the air filter. I'll post updates soon. :thinking:

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Nice! I did a similar thing on my KLX300 but ran the filter into the air filter box to keep it from getting too dirty. Not sure if you can find a route to get back there but it's an idea that worked great on my KLX.

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Big mistake, you need to run vent hose up high to frame and then back down to air box to avoid water capture and run back into engine. Good routing more important than filtering on the end

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Big mistake, you need to run vent hose up high to frame and then back down to air box to avoid water capture and run back into engine. Good routing more important than filtering on the end

 

 

The problem with running the tube anywhere above the crankcase is a flaw in Kawasaki's placement of the breather vent. Because it is coming directly out of the crank that means that you have to counteract the siphon effect if the bike happens to get lied down on its side more than 90 degrees. When riding in Glamis or Ocotillo this can happen a lot for me. To do this you have to route the tube high then back below the crank so that the pressure of the fluid on one side will be equal on the other without is spewing out of the breather. I have even contacted Kawi tech to ask if I can relocate the breather and according to them for whatever reason I cannot I think a great spot would be on the valve cover and with the two filters you wouldn't have to worry about dirt or sand getting in. Then you could route it to the air box or somewhere else high and dry while minimizing the siphon effect. Anyways, where I have it now and what seems to work the best is ending the tube at the stock position where the breather filter will not fit. I ran longer tubing up higher and kept the fuel filter in the line to catch blowby oil and also catch any grime that may possibly make it that far up into the tube. I change this filter with each oil change and I have never once found grime inside of it yet so it is working great for me.

 

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I have just come across this thread,I have a KLX450R with kx450f air box so I run the kx crank breather hose,I ran it into the void of the bashplate but have just converted my bike to supermoto and didn't want any oil making it's way near the rear tyre so I pretty much came up with this idea also,I have just ridden the bike for the first time and noticed some milky oil in the crank breather filter...

 

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it wasn't raining and the hose continues on up and the down into a filter on the end of the hose,I have drained my oil and it has come out normal,could this just be some remaining moisture as the bike has sat for a few months whilst I did the conversion,it has only been started on a weekly basis to keep it going but not ridden,I have never seen oil that comes out of the crank breather so I'm not sure what to expect

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That definitely is water. The concern would be that as it condenses in there it would drain into the case. Do you live in a humid, cold place and did you see this after you rode it or before?

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I saw this after taking the bike for a 10min ride,the first time the bike has been ridden in months and the first time with this breather set up,I removed the set up as soon as I saw it and then drained engine oil and there was no sign of water at all in the engine oil,so the water didn't come from the engine oil,that only leaves the breather setup,I'm thinking water has condensed there from perhaps steam getting trapped between the two filters I run and the path for air vapors is blocked with such a setup,I am now running a long breather hose that loops on it self before going up and then down and I will run a small bottle at the bottom to catch what ever comes out and ill see if I get the same milky oil or not

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Exactly, when the bike is being ran you are pushing pretty hot air through there, which will cause everything to heat up. As it cools the water in the air will condense only the cooling plastic. I have not had this problem yet, being in California it is fairly dry. At the same time, you can occasionally see steam blown out of these tubes with blow by, so this is not a problem that stops just because you would remove the filter. The filter makes it easier to see.

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Spoke to my suspension tuner about it as I'm bout to get suspension work done(he's a mechanic as well) he mentions that cause I ran the fuel filter and the smaller K&N filter that the steam/hot air/vapors is trapped between the two filters and in the paper element and then settles as water,having no filters means steam goes straight out the hose,I have removed the setup and just run my hose straight up and then down into a clear bottle,after another ride today there was no oil residue or milky water/oil in the bottle,but that's not to say it was cause it never got high enough to drain into the bottle,I might run a shorter hose to see what comes out first

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