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zac_atac44 Samba Member
Joined: September 18, 2011 Posts: 269 Location: Tennessee
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Posted: Tue Apr 08, 2014 6:19 pm Post subject: Correct way to vent the crank case |
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Anybody have any advice or know of any articles that describe the correct way to vent the crankcase? I have a 2332cc I am building and want to make sure this is right. Thanks to all and hope all is well. |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76937 Location: Sneaking up behind you
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Posted: Tue Apr 08, 2014 6:24 pm Post subject: |
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Start with valve covers. If there's a problem add a case vent. _________________ Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"
Member #1009
#BlueSquare |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4343 Location: Los Angeles, CA 90016
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Posted: Tue Apr 08, 2014 7:13 pm Post subject: |
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This is going to open up a can of worms.
My experience: I've never needed valve cover vents. On small CC engines (1915 and down) I vent through the fuel pump location and use the stock oil filler vent with the road draft tube. On larger CC engines, I've had issues with the valve cover vents and oil filling the breather box. I added a third vent to the case and the problems went away.
The way I see it, the case pressure is localized first in the case, so why not vent at the source? _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Tue Apr 08, 2014 7:41 pm Post subject: |
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bugguy1967 wrote: |
This is going to open up a can of worms.
My experience: I've never needed valve cover vents. On small CC engines (1915 and down) I vent through the fuel pump location and use the stock oil filler vent with the road draft tube. On larger CC engines, I've had issues with the valve cover vents and oil filling the breather box. I added a third vent to the case and the problems went away.
The way I see it, the case pressure is localized first in the case, so why not vent at the source? |
Bingo, couldn't agree more.
I run a big 3/4" breather off the alternator stand on my race motors and eliminated all of my valve cover vents entirely. ALL of my oil blowby issues went away when I did that.
Crankcase pressure doesn't start in the valve covers, so why vent there first? Vent the source. The case. _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4343 Location: Los Angeles, CA 90016
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Posted: Tue Apr 08, 2014 8:01 pm Post subject: |
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I believe I've asked before, but could you please send me a link to that valve you have on your header to connect to an oil can?
I'm guessing the box has to be sealed and you need a sand seal as well, correct? _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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rrcade Samba Member
Joined: May 29, 2010 Posts: 735 Location: WI 1962 Bug 2276
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Posted: Tue Apr 08, 2014 8:03 pm Post subject: |
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Is there such a thing as too much venting? |
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zac_atac44 Samba Member
Joined: September 18, 2011 Posts: 269 Location: Tennessee
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Posted: Tue Apr 08, 2014 8:07 pm Post subject: |
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Quote: |
Is there such a thing as too much venting?
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Good question!!!! |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4343 Location: Los Angeles, CA 90016
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Posted: Tue Apr 08, 2014 8:15 pm Post subject: |
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I don't think so as long as you're venting from the right areas. If the valve covers had a built-in baffle, I don't see why they couldn't be vented as well, but they typically don't.
A bit of vacuum actually works a lot better than just openings where the pressure can escape. Most would have a hard time NOT getting their rings to seal with an exhaust-driven vacuum source like Eaallred has, or had.
Edit: maybe even a baffle couldn't stop that tidalwave of oil coming in at high RPM. Add a drain for the oil to return to the sump, then a vent can be used properly. _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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Juanito84 Samba Member
Joined: March 17, 2012 Posts: 2436 Location: Colorado Mountains
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Posted: Tue Apr 08, 2014 8:41 pm Post subject: |
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Here's my 2 cents.
Crankcase fumes are corrosive to your engine's innards, so try to set up the crankcase ventilation so that it not only relieves crankcase pressure, but it also circulates, so that fresh air enters and fumes exit. You can use the stock entrance and exit (the unsealed pulley and the alternator stand) or make your own, pehaps putting a sand seal on the pulley and a filtered inlet on a valve cover.
IMO, if set up right there is no reason to vent fumes into the atmosphere. These fumes can be recirculated back into the intake to burn up any unburned fuel left in it. Plus the intake can help pull in these fumes and therefore help fresh air circulate inside the crankcase. This can be done with a PCV valve or just using the restriction caused be the air cleaner like stock, although most stock VW systems incorporated a flap on the air cleaner to provide the right amount of suction for proper circulation.
The crankcase is full of oil spray so it is likely that you will get oil in your crankcase "exhaust". Oil, of course, will increase the chances of detonation and foul the spark plugs. You can reduce oil spray by using a ventilation tower so that air flow slows down causing oil droplets to fall from suspention and collect in the bottom of the tower where the oil drains back into the crankcase. Again, you can use the stock alternator stand for this or make your own. Or just vent to the atmosphere.
It has been noted that the left valve cover tends to fill up with oil at high RPM, and venting this cover may make things worse. However, there may be ways to stop this problem and still vent the left valve cover.
I haven't heard of anyone doing this on a VW engine, but some hotrodders put a vacuum pump on the crankcase. This lowers the aerodynamic drag caused by the crank and rods and keeps the rings seated. The downside is that you lose some oiling advantages caused by swirling air in non vacuum crankcases meaning you may have to put oil spayers on everything not pressure fed.
http://www.vw-resource.com/air_cleaner.html#crankcase _________________ If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine? |
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bugguy1967 Samba Member
Joined: January 16, 2008 Posts: 4343 Location: Los Angeles, CA 90016
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Posted: Tue Apr 08, 2014 9:23 pm Post subject: |
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There are plenty of vacuum pumps on VW engines; just not on street engines. I hear they pull oil away from the valve cover area in some sort of negative way and aren't suitable for street use. It seems to me that by slowing the pump down enough by swapping pulleys could work for the street. _________________ "A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine" |
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Type 5 Joe Banned
Joined: January 18, 2003 Posts: 1795 Location: Oregon
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Posted: Tue Apr 08, 2014 9:27 pm Post subject: |
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Well that is a pretty far-out theory... I would add a pine tree air freshener to the crankcase air inlet. |
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Tue Apr 08, 2014 10:12 pm Post subject: |
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You can't vent a case to much. But you can pull to much vacuum on an engine and starve the rings and wrist pins of oil. A typical vacuum pump system has a relief valve to limit the amount of vacuum.
I run a vacuum pump on the street car, limited to 12" vacuum. A couple solenoids control the system to make the system act like a regular breather and drain the catch tank below a set rpm and throttle position.
The rail runs a typical crank case evac system since space is limited.
I tried a pair of 3/4" drain lines to the sump from the valve cover which didn't do a lot to fix the oil issues i was having at the track. Eliminating the valve cover vents and venting the case did.
As of 5-6 years ago you will never see a valve cover vents on any vw of mine. _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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Juanito84 Samba Member
Joined: March 17, 2012 Posts: 2436 Location: Colorado Mountains
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Posted: Tue Apr 08, 2014 10:56 pm Post subject: |
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A guy could try an electric air pump and get circulation and a mild 3" hg of vacuum.
http://www.turbo-mopar.com/forums/showthread.php?27978-Electric-crankcase-evacuation-pump
I wouldn't draw off the valve covers, but I do believe if you hook up filtered intake air there it would be benificial as long as you have something pulling out the fumes elsewhere. But what do I know? _________________ If a water cooled engine cools its water with air, isn't it just an overcomplicated air cooled engine? |
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Quokka42 Samba Member
Joined: December 02, 2010 Posts: 3117 Location: Melbourne, Australia
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Posted: Wed Apr 09, 2014 3:24 am Post subject: |
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I think the venting of valve covers is a "monkey see, monkey do" - guys have seen a return to valve covers and incorrectly assumed it was being vented from there. Unless you have really bad exhaust valve guides the valve covers should have negative pressure, as the main blowby is past the rings into the case. _________________ There has only ever been one man who was perfect, and they nailed Him to a cross. |
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vwracerdave Samba Member
Joined: November 11, 2004 Posts: 15308 Location: Deep in the 405
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Posted: Wed Apr 09, 2014 4:52 am Post subject: |
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I have a different opinion. I feel the valve covers need to be vented so oil can return to the case much quicker. Where you install vents on the valve cover is important and looking in the picture gallery many people install vents in the wrong place. They need to be on the top at the front of the engine. On my 2276 that sees 7000 RPM I vent both valve covers, fuel pump location and oil filler tower. I use the cheap $30 Bugpack breather box and not a drop of oil comes out the top.
The left 3/4 valve cover Filling with oil can be reduced if you follow all the Bob Hoover HVX mods.
You should never vent to the air cleaners. _________________ 2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK |
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Alstrup Samba Member
Joined: July 12, 2007 Posts: 7216 Location: Videbaek Denmark
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Posted: Wed Apr 09, 2014 4:59 am Post subject: |
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Dave. As long as you go in a straight line that works. if the same set up was to be used on an engine that takes high G impacts it would fill the breather in no time flat.
I concur with the crank case breathing. The pressure in the valve cover area HELPS send oil back to the case faster than with vents on. IF one needs to vent the valve vovers for what ever reason, one of the tricks to make it work properly is to reduce the hose to 1/4" and then connect it to the center beather box.
T |
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Matthew Samba Member
Joined: January 29, 2004 Posts: 1760 Location: Eastern Tennessee
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Posted: Wed Apr 09, 2014 5:02 am Post subject: |
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Type 5 Joe wrote: |
Well that is a pretty far-out theory... I would add a pine tree air freshener to the crankcase air inlet. |
Best response ever on this hot topic, Lol! _________________ 1965 Beetle sedan
Click to view image |
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Eaallred Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Wed Apr 09, 2014 5:45 am Post subject: |
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Venting a valve cover has no benefit to aiding in oil draining back down to the case. In fact it makes it worse.
With no venting at the cover, there is no air flow up the pushrod tubes so oil can drain back without resistance. With a vent in place you now have a path for air flow. Now crank case pressure is flowing up the tubes to the valve cover area. This adds resistance to oil flowing back down to the case as well as contributes to flowing more oil mist and windage up to the valve cover area. _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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raul arrese Samba Member
Joined: July 23, 2006 Posts: 1330 Location: miami florida
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Posted: Wed Apr 09, 2014 5:57 am Post subject: |
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If your case is vented correctly there is no reason for valve cover vents .. my 1 cent |
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VWCOOL Samba Member
Joined: June 02, 2006 Posts: 1821 Location: Down under
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Posted: Wed Apr 09, 2014 7:42 am Post subject: |
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Extra crank-case venting is really only required in circumstances of excessive blow-by due to worn rings or poor engine machining/assembly. If your rig is straight and rings sealing correctly, you should have little more blow-by than a stocker... so the stocko VW system is a simple and inexpensive place to start.
Some track/comp classes require a breather box... which is why I have one of the $20 Bugpack widgets on my 1916 comp donk.
Venting from the fuel pump location is not ideal as oil flung from the cam gear gets cast straight up the vent tube...or so I have been told. I have never experienced it as I have never a breather to that location
Hope this helps
Last edited by VWCOOL on Wed Apr 09, 2014 7:48 am; edited 2 times in total |
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