Crankcase vacuum inquiry!

CydnyVicious · Posted: Sat Jun 02, 2012 3:09 pm Post subject: Crankcase vacuum inquiry!

Advice -
So, we have a 74 Thing with a freshly rebuilt engine; larger intake manifold and aftermarket carb with fancy chrome air filter.

The vacuum tube leading off of the Oil Fill tube to the air intake no longer provides enough suction, due to the aftermarket air filter and carb. We now have oil leaking from every seam, due to the lack of negative crankcase pressure (no vacuum). Any advice on how to resolve this? I'm thinking as a last resort, I could drill & mount a port on to the intake manifold that the vacuum hose can attach to. I'm wondering if there is any sort of a spacer or something that could mount between the intake manifold/ carb with a vacuum port.

For a perfect description of the problem we're having, see the crankcase ventilation section at http://www.vw-resource.com/air_cleaner.html as well as the first bullet point under Aftermarket Air Cleaners.

Thanks!

FV195 · Posted: Sat Jun 02, 2012 3:50 pm Post subject:

hose should go to your air filter, that will cause the - pressure your looking for

CydnyVicious · Posted: Sat Jun 02, 2012 4:11 pm Post subject:

Nah, that's the problem; it's connected to the air filter by default; since the new, aftermarket air filter is wide open, there's not enough suction from the carb. The vac hose connects to the bottom of the new air filter- which is rectangular & open on all sides.

uberautowerks · Posted: Sat Jun 02, 2012 5:13 pm Post subject:

Firstly....
What size engine??
What carb?? (unfortunately "larger intake manifold" doesn't quite cover it.)
Where, specifically, is the oil coming from? (If indeed "Every seam" you have other more critical issues which are outside the realm of air cleaner venting)

Ok now the helpful bits....

I'm sorry to say that you have misunderstood what you read regarding crankcase ventilation.

From the referenced article.... "This oil mist, of course, settles out inside the engine compartment and can make a real mess."

The key point here is "Oil Mist" NOT "leaking from every seam".

Improper crankcase venting MAY, perhaps, cause massive leaking IF the vent is simply plugged or plumbed into the cooling fan pressure system.

If you have SOME oil seepage from behind the crank pulley and maybe around the oil cap you MAY have some issues which couple be solved with a different air filter.

On the other hand, if you have MASSIVE oil leakage from behind the crank pulley and perhaps the dipstick.... than you have a completely different problem. Typically too much blow-by from improperly seated or installed piston rings.

Fact #1 I personally have run lots of engines over the years without any breather hose to the air cleaner. Rather the hose was routed under the engine with a small filter to keep crap out. And NEVER had it cause leaking.

Fact #2 Volkswagen didn't add a breather hose to the air filter until... um... perhaps the '60's. And even then there was a vent to the ground until '73. They only deleted that fitting because of environmental regs.

Questions???
_________________
--- The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair.
- Douglas Adams -
---
'74 Thing (White)
'71 Single cab (White too)
'70 Weekender (White three)
'05 Evolution VIII (White also!!!)
'68 F-250 (White over black)

Ian Epperson · Posted: Sat Jun 02, 2012 8:54 pm Post subject:

X2 what UberAutoWerks said. There doesn't need to be a vacuum for the crankcase breather to work as the crankcase is under slight pressure due to oil heating and blow-by. To be good to the environment, that breather is piped into the intake, but works just fine for your engine if it's vented to the ground like on older VW engines.

When I first fired up my new engine, I had a bunch of oil leaks in the oil cooler and filter that I rigged up, but they were all due to using a lousy sealer and not tightening up the fittings enough. When I helped Solomon Grundy on his new engine, he had bolted on the aftermarket oil filler incorrectly and it leaked like mad.

If you've got a really big engine, you may need to plumb the valve covers to a breather box for extra ventilation.
_________________
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CydnyVicious · Posted: Sat Jun 02, 2012 10:34 pm Post subject:

Problem seems to be solved. The vacuum hose and elbow connecting to air filter were clogged (didn't think to check since engine was just worked on), the passive ventilation was enough, we actually removed the hose and drove it around for a while without any issues. Thanks so much for your help Very Happy

uberautowerks · Posted: Sat Jun 02, 2012 10:44 pm Post subject:

Happy day!!!
Laughing

Enjoy

Eric
_________________
--- The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair.
- Douglas Adams -
---
'74 Thing (White)
'71 Single cab (White too)
'70 Weekender (White three)
'05 Evolution VIII (White also!!!)
'68 F-250 (White over black)

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50348

Since the VW system is not a POSITIVE ventilation system, but just a vent, it tends to get clogged up pretty easily with watery-oily snot. This is an all too common problem. If possible lay out the ventilation hoses in such a manner that they drain the crud readily and inspect them at every oil change to make sure they aren't getting restricted.

CydnyVicious · Posted: Sun Jun 03, 2012 9:03 am Post subject:

Got it! Thank you all so much for the help!

nikita · Posted: Mon Jun 04, 2012 2:03 pm Post subject:

uberautowerks · Posted: Mon Jun 04, 2012 5:01 pm Post subject:

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50348

nikita · Posted: Tue Jun 05, 2012 7:22 am Post subject:

The charcoal canister is hidden away behind the firewall and those hoses just disappear. Stock air cleaner has two fittings, one for crankcase vent and another comes from the canister. Most folks dont have a clue about this plumbing. On mine, the stock air cleaner was replaced with the typical cheap chrome one with one hose fitting. What did they do? Left that fitting open and pressurized the crankcase. Brilliant!

PO couldnt figure out why heater boxes were getting oiled, so he went with bolt on cast aluminum rocker covers. All the oil mist came out behind the pulley. On top of that, the oil darkened quickly and engine sludged up. After correcting the plumbing (stock air cleaner was included with bag of spare parts) a quick flush with Chevron Delo 400 and all is good.

CritDicks

I just found the tube going from my after market air cleaner to the oil filler was sludged. Drained it and blew it out. Simple fix that debilitated my '71 for winter. Ready to go for summer!!!

Wildthings · Samba Member Joined: March 13, 2005 Posts: 50348

One thing I have added to many of my VW engine is a hose coming off the fan and dumping air into one or both of the rocker boxes thus bringing in a bit of cool dry air to help clear the moisture out of the crankcase. This line has to be filtered and metered or you are going to get way too much air coming in and will blow oil out everywhere. I just use an inline fuel filter to filter the air and an orifice of about 3/64" diameter to restrict the flow. This is enough to prevent sludge buildup during winter operation and lets me run longer oil change intervals year around.


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