Crank case breather

Rickrod · Posted: July 26, 2009, 3:18 pm Post subject: Crank case breather

I have done some reading here about some of you who have installed a valve on the crank case breather.
I do not know too much about them but, as I understand they lower crank case pressure and help with oil consumption.
I'm riding a SF compression is 135 left 140 right.
repaired some oil leaks and I'm using about 10oz every 75 miles.
running Rotella 15-40
Bike feels real good to me
Left cylinder is a little hotter than right 250 to the left of spark plug.
Have 137.5 mains with XS John needles.
If you can direct me to the tread that explains it i would apprieciate it. Have tried but, cannot seem to find anything that helps me wrap my head around it.
Tia
Rick

xsjohn · Posted: July 26, 2009, 3:29 pm Post subject: Re: Crank case breather

Lets the air out as the pistons go down and closes off as the pistons go up.........bit of a negative pressure is created if the valve is accurate.......but the higher the rpms the better (guicker) the valve needs to be......made my own.......checked mine and there is a tiny bit of nevatgive pressure where it was positive before...(all this measured) .....is that enough who knows......seems better than positive though...........and my left no longer puffs a bit of smoke when it's cold from the oil thats collected in the stock breather hose (on the left) when the bike is left overnight on the sidestand (leaning left)..............

xsjohn

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Here are the posts Web Page Name And Web Page Name

Tomterrific · Posted: July 26, 2009, 4:38 pm Post subject: Re: Crank case breather

I'm the guy who brought the check valve breather concept to the XS650 list. I'm not the first to try it as some of the Brit bike guys have been experimenting for years and I had a check valve on my Triumph before the XS.

The concept is simple. Look at the under side of the pistons and the interior of the crank case. The pistons go down and air is pressurised and forced out the breather. The pistons go up and air is sucked in. The problem is the pressure when the pistons go down pushes oil out of every little space it can find. By using a check vale on the breather, air is free to go out but is stopped coming in. The resulting vacuum helps keep the oil in the engine and seals the piston rings better.

Not every valve will work. A PCV valve from a car checks in both directions. This is something not many people know so don't use a PCV valve even if somebody suggests one. I use a Power Brake Check Valve which is a generic part for an old American car. Easy to get, cheap and tried and proven. It plugs right in to the existing breather hose. Blow through the valve to get the right direction and remember the crankcase must breath out.

Tom Graham

xsjohn · Posted: July 26, 2009, 4:44 pm Post subject: Re: Crank case breather

Good job for bringing this up Tom.............better than just sucking oil as we go along or smelling it as we wait for the light......................

xsjohn

LDO107 · Posted: July 26, 2009, 5:39 pm Post subject: Re: Crank case breather

Tom,
great post. The crankcase breathing thing has been a discussion for a long time!

Can you provide a pn or place to buy the check valve?

Thanks,
LDO

Rickrod · Posted: July 26, 2009, 6:45 pm Post subject: Re: Crank case breather

Thanks all its a lot clearer to me know

Rick

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

I took my dip stick out the other day with the bike running and there sems to be allot more in and out presured down there than at the top breather. I am considering puting a check valve on top. Wonder if it would help to modify oil cap and put one that lets air in at the oil fill. Anyone ever notice this, should thetre be that much air movement by the oil fill? I think I read somwhere of a guy who builds and I think sells a setup to have a check valve at bottom crank case and one up top, it wasn't xs spesific. Does anyone have that link,?

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