Reed valve; breather?

[oldnortonrider]

(?) Anybody ever installed a reed valve (one-way) on the crankcase breather tube on one of these fine transverse-4 XS11 engines? Or any other 2, 3, or 4 cylinder motorcycle engines?

[CatatonicBug]

I had one on mine when I got it, and it was all clogged up with oil and gunk. The other end should be connected to the airbox, but if you've removed the airbox, most folks just put a small air filter thingy on the end and strap it up inder the seat.

[oldnortonrider]

Had been thinking about trying one like is shown on 'MikesXS'. I use the cone filters, so would definitely have a 'collector' or some kind of filter on the end of the line, and keep track of it, to not get clogged up.

[dbeardslee]

I've got one on mine. I just went to the local autoparts store and found a PCV valve that fit where I wanted to mount it, and put it right on the end of the breather hose with a little filter on the end of the valve. Works like it's supposed to, but it won't keep it from gassing you out at the stop lights. That's probably a good indication of when it's getting plugged up though - no fumes when fully warm should be the indicator of 'time to change the valve.' Or you can just check like you do with a car - shake it and see if you hear the rattle.

[oldnortonrider]

Yep; had also thought about going to the local autoparts store and getting some type of PCV valve to accomplish the same result. Dbeardslee, did you notice any difference~~engine response~~after putting the PCV valve on the breather line?

[dbeardslee]

I think Mikes claims a couple hp increase, but it's not something your going to notice. The reason I put it on was to hopefully get a little negative pressure inside the crankcase. I figure the less air pressure there is on the oil, the less likely it's going to find a way out.

[WMarshy]

I think Mikes claims a couple hp increase, but it's not something your going to notice. The reason I put it on was to hopefully get a little negative pressure inside the crankcase. I figure the less air pressure there is on the oil, the less likely it's going to find a way out.

PCV is not a vaccum generator, just a one way valve, therefore your crank pressure will never be negative, or less than it would on any other give day... Crank pressure is always greater than atmosphere thats why "air" comes out of the case... ... but you already knew that, just pointing it out to people who didnt know.

[natemoen]

PCV is not a vaccum generator, just a one way valve, therefore your crank pressure will never be negative, or less than it would on any other give day... Crank pressure is always greater than atmosphere thats why "air" comes out of the case... ... but you already knew that, just pointing it out to people who didnt know.

Hmmmmmmmmmm

[dbeardslee]

PCV is not a vaccum generator, just a one way valve, therefore your crank pressure will never be negative, or less than it would on any other give day... Crank pressure is always greater than atmosphere thats why "air" comes out of the case... ... but you already knew that, just pointing it out to people who didnt know.

The pistons, and specifically the blow by past the rings is what creates the pressure, and it's created in pulses. The pcv valve prevents air from re-entering through the breather hose in between the pulses. Gotta disagree - I believe it does lower the pressure.

[xs11lover]

I have one that I picked up from Mike's, but never put it on. I was thinking it would be as good as a breather filter because it's closed unless there is force pushing out. If it added hp then that was ok too. Then had second thoughts because it was for a 650. I'll try it out.

[WMarshy]

The pistons, and specifically the blow by past the rings is what creates the pressure, and it's created in pulses. The pcv valve prevents air from re-entering through the breather hose in between the pulses. Gotta disagree - I believe it does lower the pressure.

While I do agree there will be pressure pulses from the individual pistons, the fact remains that the internal net pressure of the crank case remains positive and greater than atmosphere, if vented to atmosphere. The differential pressure between the crank case and the atmoshpere provide the force to expell the fumes. The correct application of a PCV generally requires the lower pressure (outlet) side of the valve to be hooked to the intake plenum, where by it would create a vaccum due to the lower than atmospheric pressure in the plenum. Without hooking the exhaust side of the PCV up to the plenum I dont see how it would be any lower than atmosphere... Hope that isnt as muddy as it was in my head.

[dbeardslee]

If there was always positive pressure on it the valve would never close.

[WMarshy]

Yep, thats what Im sayin... If that wasnt true, your theory would mean the PCV cycles open/closed potentially up to two times for every piston that completes a revolution..? for a total of 8 times for every revolution of the crank...?

[dbeardslee]

Here's what wikipedia has to say about it -

Before the invention of crankcase ventilation in 1928, the engine oil seals were designed to withstand this pressure, oil leaking to the road surface was accepted, and the dipstick was screwed in. The hydrocarbon rich gas would then diffuse through the oil in the seals into the atmosphere. Subsequently, it became an emissions requirement as well as a functional necessity that the crankcase have a ventilation system. This must maintain the crankcase at slightly less than atmospheric pressure under light load conditions and recycle the blow-by gas back into the engine intake.

[cywelchjr]

If there was always positive pressure on it the valve would never close.

The valve actually is designed to allow a certain amount of vacuum to be applied to the crankcase instead of the crankcase being vented to air. The valve by itself would from what I know of their operation actually increase the pressure in the crankcase with no vacuum applied to the other side. Here is a wikipedia article on the device.

I think it explains things reasonably well.