Crankcase Vent Hose Mod


11 replies to this topic
  • SXP

Posted November 07, 2005 - 08:48 PM

#1

After a near drowning this weekend that resulted in an airbox full of water and water sucked up the crankcase vent hose, I had a brain wave :banghead:. Instead of re-routing the hose to the airbox etc., why not put a one way valve at the end of the hose (if someone else has already thought of/done this, my apologies for claiming credit). A quick trip to Autozone and $2.99 later I came home with a PCV one-way valve:

http://img.photobuck...od/DSC06659.jpg

And after installation I ended up with this:

http://img.photobuck...od/DSC06662.jpg

There were a whole bunch of different style of PCV valves to choose from but I deliberately choose the angled/elbow type to direct the blow-by away from the skid plate to avoid the usual mess. The mess on the bike if from yesterday's ride (pre-install).

  • RADRick

Posted November 07, 2005 - 09:17 PM

#2

Bad idea, unless you like replacing gaskets and possibly damaging your engine. The breather system needs air to flow in AND out in order to properly ventilate the crankcase. The one-way valve will cause pressure build up that needs to go somewhere. Remove that contraption before you do some damage.

  • SXP

Posted November 07, 2005 - 09:22 PM

#3

My understanding is that the hose always blows when the engine is running, and only sucks when starting (no puns intended). So, if I understand what you are saying if I'm in footpeg deep water with the engine running I'm sucking water into my engine? I can't believe Yamaha would have left the end without a filter if it sucks air in while running. Wrong? Right?

  • WildRide

Posted November 07, 2005 - 10:08 PM

#4

Bad idea, unless you like replacing gaskets and possibly damaging your engine. The breather system needs air to flow in AND out in order to properly ventilate the crankcase. The one-way valve will cause pressure build up that needs to go somewhere. Remove that contraption before you do some damage.

I agree. The piston goes up and down displacing a volume in the crankcase= air going in and out. I tried putting a small chunk of a course stainless steel pan scrubbing ball in the hose up right after the valve cover outlet nipple. My theory being it acting like a baffle for oil droplets and mist yet still allowing air flow. Well even though It was only loosely installed and did not plug the tube, it still caused enough back pressure to force a small amount of oil out past the clutch actuator lever shaft, I removed it right after and the shaft leak stopped.

  • grayracer513

Posted November 08, 2005 - 11:29 AM

#5

I was invited to give my opinion on this, so here it is:


I like the idea of a one way valve at the breather, but I don't think that a PCV valve from a car is a good choice because I don't think it allows enough air flow. Remember that the are supposed to prevent intake backfires from entering the crankcase, and allow a METERED flow of air out of the crankcase. So, it would probably be too restrictive.

A simple rubber "reed" valve like you see on the drain tubes of some air boxes would be what I would use.

Under way, with the rings sealing perfectly (which, of course, they don't) the crankcase pressure is up on the downstroke, and down on the upstroke, for a net of zero. The air moves in and out through the breather as the piston moves at low RPM, but it can't move fast enough to match the piston pulse for pulse at higher speeds. The practical reality is that the rings leak combustion pressure into the crankcase so that, under power, there is a net outflow. As far as there being a risk of picking up dirt, pull the hose off the cam cover and wipe the inside of it with your finger. You won't find any.

The trouble really starts when cranking the engine. At that low speed, the air has enough time for a full 450cc to pass out and then back into the engine, so the potential for drawing water up into the engine becomes more realistic.

You would not, however, want to use a total one way check. The engine will run just fine with a crankcase vacuum of up to maybe 8-9 inches in the crankcase, if one was created, and in fact, a lot of drag racers set systems up to cause exactly this. A vacuum in the crankcase means less air in the way of the piston. But too much will pull air in past the engine seals, or even pull gaskets out of place. And then, too, the engine will cool off when you park it, adding to any such vacuum if the ventilation were truly one way only.

So, what I would do is to leave the breather in the stock location, either add the reed to the bottom end, or not, and put a "T" in the pressure balance tube running from the oil tank to the cam box. Then, run the small (it can be very small) hose from the "T" up and down into the steering stem with the gas tank vent. This small hose will break any vacuum that gets created in the breather while cranking the engine (Of course, with the one way check at the bottom, there's no chance of it even trying), so that it would not be capable of raising water far enough to bring it all the way into the engine, and located down the stem, it is very well protected from contamination itself.

  • RADRick

Posted November 08, 2005 - 12:39 PM

#6

Not to impugn Gray's lengthy explanation, but the simple reality is that the crankcase breather system needs unimpeded flow both ways to work properly, whether at start or running. PCV valves for cars are not designed for the kind of environment a dirt bike is subjected to. For one, on a car they aren't subjected to extreme changes in attitude and impacts. Also, the springs inside them that hold the check ball are designed for the vacuum of a specific engine. Since I don't know of any single-cylinder cars then finding one appropriate to a dirt bike may be difficult. Certainly, guessing by looks won't work. I still maintain that the best solution is rerouting the hose to the air box. The miniscule amount of oil vapor that makes it out the hose will not impact performance and it will be up and out of the way in the event of a water incident. I documented this mod in the May '05 issue of Dirt Rider and have used it on many of my bikes (including my Harleys) for years.

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  • byggd

Posted November 08, 2005 - 12:48 PM

#7

I remember reading a thread where a TTer slipped a larger clear hose up over the stock hose up to mid way up the radiator that was lose enough to allow the engine to breath in both directions and then at the bottom of the clear hose he put a valve that could be opened to drain off any oil that collected. He said it worked really well as long as you don't submarine the bike up past the middle of the radiators.

  • tony1970

Posted November 08, 2005 - 02:13 PM

#8

I think your safest, easiest, and best bet is running the tube to the airbox like they did in Dirt Rider a few months back. They did it on an '04, but I would guess it would be the same for your bike.

  • gloft

Posted November 08, 2005 - 03:02 PM

#9

I put a t type pvc fitting just at the top of the valve cover and cut the tube to extend down just as stock but when return flow is restricted i.e., you're in water up to the engine, the engine will draw from the upper end of the T fitting. Since this time, I've had 0 problems with deep water stalls and restarting. I tried the DR mod and I would NOT recommend this to anyone unless you route the hose into the top of the air box. If you drill a hole at the bottom, the motor can draw in water when swamped :applause:

  • tony1970

Posted November 08, 2005 - 04:40 PM

#10

I put a t type pvc fitting just at the top of the valve cover and cut the tube to extend down just as stock but when return flow is restricted i.e., you're in water up to the engine, the engine will draw from the upper end of the T fitting. Since this time, I've had 0 problems with deep water stalls and restarting. I tried the DR mod and I would NOT recommend this to anyone unless you route the hose into the top of the air box. If you drill a hole at the bottom, the motor can draw in water when swamped :ride:


I better call Yamaha Design department and complain where they put my crankcase hose on my '05 because it is in the middle of the air box. The DR mod placed the vent hose in the top left corner of the airbox. This seems the most foolproof way to me to keep water out, but to each their own. :applause:

  • RADRick

Posted November 08, 2005 - 06:19 PM

#11

I better call Yamaha Design department and complain where they put my crankcase hose on my '05 because it is in the middle of the air box. The DR mod placed the vent hose in the top left corner of the airbox. This seems the most foolproof way to me to keep water out, but to each their own. :applause:

Since I wrote the DR article in question I can unequivocally say that it shows the hose mounted at the top of the airbox and directly over the filter. This was done for two reasons: 1) water and debris will collect in the bottom of the airbox and could possibly be sucked into the breather hose if mounted low enough. 2) any oil mist that finds its way into the hose will fall harmlessly onto the filter element where it will simply add to whatever substance you use to lubricate the element. :ride:

  • Captain Bob

Posted November 08, 2005 - 07:15 PM

#12

I repositioned my vent hose on my 99 WR totally different then any example I have heard on this thread. After removing the clear tube from the airbox drain, I ran the vent hose directly to that drain. I then determined where the low spot was in the vent hose (now connected to the drain). I cut the hose at the low spot and inserted a 1/2 inch plastic T fitting (pointing downward). I took the clear tube and reattached it to the portion of the T fitting pointing down. Done! I arranged it in a manner so as not to interfere with chain. If you want a pic, let me know.

The vent hose can breath, water can drain out of the airbox, and all I have to do is remove the clear tubing to drain water/oil. I can now go through serious water or, start my bike in water without worrying about the vent hose sucking it in. I figure my only risk is if I drop the bike (while running) on its side in deep water. This however, is an issue regardless where the vent hose is placed. This took all of 20 minutes to complete. Hope this helps!

Bob




 
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