3 days in sand, now I need a full rebuild

[albertaguy]

A variation on the reroute is to mount the T fitting directly above the cam cover port, and then run the original stock breather down the front just as it is. Then run the new section back and into the airbox with an added filter as in the pictures here. That splits the breather exhaust into two directions, and the strength of any vacuum pulse is cut in half as well. If and when the lower tube would try to lift anything heavy, air will rush in through the top section instead, being the path of less resistance.

This question probably stems from my lack of understanding of why the hose is there in the first place (don't remember there being one on my 05 crf). Is there a need to have a downward / gravity component to the breather assembly? Does oil ever come out and need to go down hill. I had wondered if there was ever oil in the hose could sand wick its way up the oiled hose? If there is a good reason to leave a hose down plus take one back to the air box with a filter on it I will go that way. Looking at the new wr's they go into the air boot which is fine as a factory item and no need for another filter but I wouldn't dare rig something like this (but still no downward component). Perhaps the 08 wr boot with its coupler would fit on the yz's. That would be the most factory setup. Anyone done this? I even had friends reroute their breathers into the air box before this happened to mine but I thought without a filter on it that's almost worse as the air box fills with sand and dirt over time and then gravity would be working against you as garbage bounced it's way down the hose into your engine. It only made sense for water. Long question short why the need for,or the possible benefit of the downward hose?

[grayracer513]

This question probably stems from my lack of understanding of why the hose is there in the first place (don't remember there being one on my 05 crf). Is there a need to have a downward / gravity component to the breather assembly? Does oil ever come out and need to go down hill. I had wondered if there was ever oil in the hose could sand wick its way up the oiled hose? If there is a good reason to leave a hose down plus take one back to the air box with a filter on it I will go that way. Looking at the new wr's they go into the air boot which is fine as a factory item and no need for another filter but I wouldn't dare rig something like this (but still no downward component). Perhaps the 08 wr boot with its coupler would fit on the yz's. That would be the most factory setup. Anyone done this? I even had friends reroute their breathers into the air box before this happened to mine but I thought without a filter on it that's almost worse as the air box fills with sand and dirt over time and then gravity would be working against you as garbage bounced it's way down the hose into your engine. It only made sense for water. Long question short why the need for,or the possible benefit of the downward hose?

Oil does exhaust from the breather hose at times if the engine is run very hard. The downward route of the hose is simply the least complicated way of dealing with it, and works fine for 98% of the uses the YZ450 was built for, which was as a race bike. It does have potential shortcomings, as noted already.

Running a second hose on a split line, as I suggested, averts almost any possibility of drawing even fine sand upward into the engine. Running a single hose to the air box will work, but any oil that does get exhausted will end up slopping up the filter, etc. If you choose this method, be sure that you run a non-restrictive filter of some kind on it, because as anyone who has owned a YZF knows, the air box isn't the cleanest place in the world. If you worry about the fine dust that bypasses the air filter, don't let the breather suck it down. As you have correctly observed, the hose is shorter when routed back to the air box, and the horizontal orientation provides less protection against dirt intrusion than the vertical.

Running to the air boot ala WR450 has the advantage of allowing the engine to pull its air in from a filtered source, but there, oil that accumulates in the hose, and/or exhausts from it goes through the intake. That's far from the worst thing that could possibly happen, but it's not really that desirable, either, thus, the oil trap shown in the kit (yes, someone has done it):

https://www.thumpertalk.com/forum/showthread.php?p=4956573#post4956573

The oil trap concept is used on XR600/650's that I know of, and in that case it's actually auto draining. They accomplish that by extending the down routed oil trap segment to a point under the bike and close the hose off with a simple one-way rubber "reed" valve; pressure in the hose blows it open and dumps the oil, vacuum in the hose closes it. If you run an oil trap like this, DO NOT simply leave it open, since this would create an unfiltered air path to the carb intake. It needs some form of effective one way valve, or a plug.

And no, sand could not wick upward it the oil collected inside a down routed hose.

In my opinion, the ultimate would be to run the crankcase vent downward to a catch can, kind of like its own little air box. A second hose would come from there up to the air boot, providing a filtered air source for any air that flowed into the crankcase from outside, and would be protected from crankcase exhaust by a one way valve allowing air to flow from the intake to the engine only. A third hose would extend from the bottom of the can to the outside, again protected by a one way valve allowing air only to run out, and not in. All exhausted oil and crankcase vapors would go out, and only clean air would go in. Whether that would be entirely worth the complexity is something you'll have to decide.

[WGP]

My 05 WR450 has the tube going to the airbox about midlevel, not the airboot. And it does ooze a little oil from time to time...

It seems this is fine since water and sand would have a hard time making it in there and its on the outside of the filter for the ooze..

[redswr]

Changed air filter 2-3 times a day with a good grease beed around the rim plus outer wear prefilter over all that.

i've always heard that a slightly dirty air filter works better than a clean one... my 07 450 has a little over 700 miles on it and more than half of those were in the sand. i've had no problems whatsoever with cleaning my air filter and changing my oil every 100 miles... same thing with my 99 that has seen probably 1000 miles of the dunes and has never given me problems.

[grayracer513]

i've always heard that a slightly dirty air filter works better than a clean one...

Wrong.

[KAS]

i've always heard that a slightly dirty air filter works better than a clean one.

There is absolutely no logic behind this.

Think about what stops the dirt from entering your motor. The clean, oiled foam. If the filter is dirty, there is nowhere for the dirt to stick.

[grayracer513]

There is absolutely no logic behind this.

Think about what stops the dirt from entering your motor. The clean, oiled foam. If the filter is dirty, there is nowhere for the dirt to stick.

Exactly. It's the oil that traps the dirt, not the foam.

[redswr]

If the filter is dirty, there is nowhere for the dirt to stick.

and... it won't let it through. it will just let the air in and the dirt will be left in the little catcher at the bottom of the air box...

BTW: i read this in either TransWorld or RacerX in a section talking about different myths in motorcross.

[nap__kxf]

and... it won't let it through. it will just let the air in and the dirt will be left in the little catcher at the bottom of the air box...

BTW: i read this in either TransWorld or RacerX in a section talking about different myths in motorcross.

no.

it will starve the engine of air which will cause loss in performance, but the engine obviously won't recgonize this and try to suck in the same amount of air which will eventually suck in the oily dirt.

[redswr]

ok... i didn't find the artical. i clean mine when its really dirty but not 3 times a day like the first poster said... thats a little excessive.

[MacJammer]

really wierd stuff guys. My '06 gets run a lot and 90% of the time it is in the sand. I change my air filter every ride and my oil every other. I had my engine torn down 2 weeks ago for a new timing chain and everything looked great. I do keep it reved up pretty good so oil and air are always going out of the breather. Maybe that is the trick. ride it hard.?

[grayracer513]

My '06 gets run a lot and 90% of the time it is in the sand.

I've never had a problem with it either, but I can see that the possibilities exist if you create the right circumstances.

If the filter is dirty, there is nowhere for the dirt to stick.

and... it won't let it through. it will just let the air in and the dirt will be left in the little catcher at the bottom of the air box...

BTW: i read this in either TransWorld or RacerX in a section talking about different myths in motorcross.

Great. Now there are myths being created in TransWorld or RacerX. ? Hopefully, it's a case of your misreading the mag.

Here's what really happens:

Foam filter media is made up of fairly large, open cell foam, meaning that cells, the "bubble" in the foam, are open on several sides, and are connected to each other. The media is therefore somewhat like a web membrane through which air and fluid can flow freely. The structure of the foam is such that while air can flow freely through, it cannot flow straight through. To improve air flow for performance reasons, the passageways in the foam are intentionally quite large, relative to the size of the particles it is expected to stop, and the dry foam would readily allow full sized 120 micron grains of sand to pass through without much resistance if there was enough air flow to pull it through.

To stop the dirt, the filter is saturated with oil so that each fiber of the foam matrix is thoroughly coated with it. As air winds its way through the element, making erratic 3 dimensional turns as it goes, the heavier dirt particles fail to make these turns and collide with the oil soaked foam and sticks to it.

This continues until the oil near the outside of the foam has absorbed and collected all the dirt it can, at which point, new dirt must move deeper into the element to find more viable oil to stick to. Depending on exactly how coarse the foam is, one of three things happen, both with one of the same results:

> In very coarse foam, the dirt continues to move deeper into the filter until it begins to pass completely through and into the engine, essentially unfiltered.

> In less coarse foam, or an element oiled with very aggressive filter oil capable of wetting and holding more dirt, the dirt moves deeper as in the coarser foams, but may also start to clog the outermost airways. This causes an increase in the vacuum under the filter, and draws dirt into and through the element and into the air stream.

> In even finer gauge foam, the filter may pack up and close off the air flow before th edirt has worked all the way through it, which will have a major negative effect on performance, if the bike stays running, beginning with the inability to take full throttle. Dirt will be forced through and into the intake in this case also.

The only dirt that will lay on "the little catcher" at the bottom of the air box is that which the air box caught by design. The function of an air box is to create a relatively still air zone (a plenum) from which air is drawn into the engine. This allows a chance for the heavier dirt particles to simply fall out of the inbound air, and allows the air to be drawn through the whole of the filter in a more uniform manner than would be possible with an air stream with a stronger velocity and direction that might tend to focus the dirty air at one spot on the filter.

In the case that you still don't buy any of this, check this out:

https://www.thumpertalk.com/forum/showthread.php?t=565418

Leave the mythology to the Greeks and whoever wrote that article. I wonder whay other "myths" they "busted".

[albertaguy]

Using outerwears prefilter really keeps things clean in the sand, you run them dry and the sand just falls off them for the most part and doesn't even make it to your nicely oiled very clean filter. There was always some down time back at the trucks between rides and we were there from dusk til dawn riding so I cleaned my air box and changed my filter all the time just to be safe. I also dropped the oil each day. We also ride all out in the dunes (like there's any other way). All I can think of is there had to be one event where all the mooms and stars lined up just right and the bike was on its side and stalled or something. Seems an uncommon occurance but frequent enough that lots of people were rerouting their hose long before this thread. Hope this has saved someone some grief. P.S. ditto on the clean air filters work best.

[bodog 24]

Is this also an issue on the 06 YZ250F?

[albertaguy]

yes, 06,07 and 08's are all in the same situation for sure - very possibly most other earlier models as well. no need for cuttimg into air boot or spending alot of money. I slid mine in just behind the gas tank into the top - front of the air box (slides past the little plastic flap that's rivitted to the air box and seals the gap between box and tank). Then I went along the side top aluminum rail (one on either side of the top of the air box). I zip tied the hose fairly snug at the front where it enters the airbox, then ran it along that side rail until almost at the back of the air box and cut off the excess hose. A second zip tie holds that end to the rail but is a hair loose so I can slide that zip tie forward allowwing me to move the hose completely out of the way when working on the air filter. Just slip the zip tie forward an flop the hose /fliter setup over the front and it's like it's not there. The filter I zip tied on very tight and it's fairly small. Just go into any auto parts store and ask to see pcv filters for late 70's early 80's fords. They are like 3$ and a few varieties to pic from and are the exact hose diameter you want. There's a few ways to do it. The filters I ended up with have a plastic housing that is curved on one side and fit perfect against the rear fender in the back of the airbox. I thought about velcroing it to that spot as well. Anyway the concept I went with is leave the air boot alone because I don't want anything getting in there, Keeping it high to be out of the water and high in the air box means less sand or dirt in contact with the filter. I liked a setup that allowed me to flop it out of the way to maintain that lovely two hand large air box on the yzfs. I'm running the pcv filter material dry but it does come out of the housing and you could oil it and maintain like your foam filter. I'll inspect it as I ride with it to see how clean it stays dry first because that's easiest. For now just breaking in the new motor so hasn't been on any long dirty rides yet with the new setup. Pretty stupid that a 3$ filter could have saved me a complete engine rebuild. It's not like it's going to happen to everyone but the chance does exist and I can't see any performance related disadvantages to rerouting. Will post pics this week.

[tnl]

My 05 had sand too at the top of my breather hose so I did this: , $4 filter from checker. I'll have to check for oil in the hose since it does not have a vertical fall after my next ride.

[albertaguy]

On the 06,07,and I assume 08's there is space to slide the hose in from the front with out cutting into the air box. Nice job and thanks for posting pics.

[WB450]

My 05 had sand too at the top of my breather hose so I did this: , $4 filter from checker. I'll have to check for oil in the hose since it does not have a vertical fall after my next ride.

That looks familiar.

[albertaguy]

Having just done mine I was wondering - I assume you run the pcv filter material dry so nothing sticks to it, probably just blow it off with air comp once in a while and change every year? They're only a couple of dollars so I didn't plan on going to great lengths maintaining it, just replace it now and then.

[grayracer513]

I assume you run the pcv filter material dry so nothing sticks to it, probably just blow it off with air comp once in a while and change every year?

That would be the wrong thing to do, since, as you say, when they are dry, nothing sticks to them.