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Tue Nov 24, 2009 5:39 pm

I am not sure why VW dropped the standard PCV valve they started with. They have tried a halve dozen breather designs over the years and nothing really seems to really shine. I can understand that with D-jet there may have been a problem with the standard valve's pulsing, but virtually everyone else managed to use them with carbs.

I like having some fresh air entering the crankcase to drop the humidity and help flush out contaminants. My 411 with L-jet runs the standard 411/412 PCV valve and vented rocker without problems that I am aware of, and my Bay has its case slightly pressurized by the cooling fan and then vents into the air cleaner, this also seems to work well.

Tue Nov 24, 2009 8:32 pm

There is a schematic for the 411/412 PCV system in the gallery. I would guess that it is like the 914 system, perhaps the same parts. I see no reason that it wouldn't work on a bus as long as the blowby under load is not any greater than a 914 engine or 422/412 engine. The only difference is that a bus climbing a hill with a load or running into the wind would see greater blowby so 914/411/412 metering might fail under those conditions. But it might be Ok too.

Tue Nov 24, 2009 10:41 pm

73kombi wrote: Having just read all 4 pages of this excellent thread...I would like your opinions on my ghetto fix for blow by. Yes my engine needs rings, and a few other things, but I was thinking a slight negative crankcase pressure would slow the oil leaks, and it has.

That's an interesting application of pressure, and suction elements in your fix. The logic works, the physical side ought to. Good luck, no leaks is a good feeling.

Wed Nov 25, 2009 8:04 am

Wildthings wrote: I like having some fresh air entering the crankcase to drop the humidity and help flush out contaminants. My 411 with L-jet runs the standard 411/412 PCV valve and vented rocker without problems that I am aware of, and my Bay has its case slightly pressurized by the cooling fan and then vents into the air cleaner, this also seems to work well.

By "vented rocker" do you mean valve cover breathers? And by "having your case slightly pressurized from your cooling fan", is that in regards to the 1/2" nipple on the top left of the fan shroud? I have very little of any stock stuff on this motor, and that hose fitting I have plugged.

SGKent wrote: The only difference is that a bus climbing a hill with a load or running into the wind would see greater blowby so 914/411/412 metering might fail under those conditions. But it might be Ok too.
I am leaning away from a PCV at this point. My test drive yesterday was 30 miles into a 30mph head wind doing about 60 (the colorado river valley gets those nasty N to S winds) coming back from Parker. I am sure I was developing significant blow by, with no apparent issues. I probably should buy a vac tester so I could actually know what is happening...yet my "regulator" metering device, doesn't appear to allow more vacuum to pass even under heavy vac loads...it remains somewhat constant, and appears to be vacuuming the case.

I am using a few copper chore boys in the breather box (like busman78) to keep the oil in the case, and act as a "flame trap" like you say, yet I don't believe anything could get by that push pin...It's a tight one-way piece.

If it continues to work like this...it will remain. If not, I'll order this setup...we had breathers like this on our sand rail.

It's cheap enough, and spare valve covers aren't too hard to find, and I could plug the holes in tin...if it doesn't work out.

Wed Nov 25, 2009 8:24 am

The AMC heads I got from HAM have 1/4 NPT ports on top left, apparently for a breather setup. Would make switching to this type of PCV system a breeze without modifying the valve covers. However my breather valve is working properly right now.

Of course this is more complex to do with the FI since you have to account for all the air and whether it's metered or not.

Some corvette engine guys run considerable negative pressure in their case, even going so far as to add vacuum pumps and run 15-20" negative. Supposedly to seal the rings better and increase oil flow. In a VW you will certainly suck in your valve cover seals at those numbers. Other than that, I think the main risk is drying out the main seals.

Wed Nov 25, 2009 9:14 am

73kombi wrote: By "vented rocker" do you mean valve cover breathers?

Yep, either a fitting in the valve covers or a fitting in the head itself.

Quote: And by "having your case slightly pressurized from your cooling fan", is that in regards to the 1/2" nipple on the top left of the fan shroud? I have very little of any stock stuff on this motor, and that hose fitting I have plugged.

I just take the air off the nipple on the fan shroud run it through an inline filter and then a small orifice (~1/16-5/64") and dump it into the crankcase. The crankcase is then vented into the air cleaner. This is with a progressive and has run this way for 20+ years. I have had no leak problems and the engine hasn't been apart since 1990. If you do have bad seals or gaskets this would NOT be the way to go.

Wed Nov 25, 2009 10:04 am

Wildthings wrote:
I just take the air off the nipple on the fan shroud run it through an inline filter and then a small orifice (~1/16-5/64") and dump it into the crankcase. The crankcase is then vented into the air cleaner. This is with a progressive and has run this way for 20+ years. I have had no leak problems and the engine hasn't been apart since 1990. If you do have bad seals or gaskets this would NOT be the way to go.

Although this setup works for you, it does have a theoretical problem. There is some blowby in your crankcase gas, some of which is already burned (inert) and some of which is not. The inert gas going through your carb will slightly richen the mixture. Not necessarily a bad thing since it will occur under high load (high blowby), but something to be aware of.

Wed Nov 25, 2009 12:36 pm

WhirledTraveller wrote: Wildthings wrote:
I just take the air off the nipple on the fan shroud run it through an inline filter and then a small orifice (~1/16-5/64") and dump it into the crankcase. The crankcase is then vented into the air cleaner. This is with a progressive and has run this way for 20+ years. I have had no leak problems and the engine hasn't been apart since 1990. If you do have bad seals or gaskets this would NOT be the way to go.

Although this setup works for you, it does have a theoretical problem. There is some blowby in your crankcase gas, some of which is already burned (inert) and some of which is not. The inert gas going through your carb will slightly richen the mixture. Not necessarily a bad thing since it will occur under high load (high blowby), but something to be aware of.

Yes the crankcase gasses will affect mixture, but with my system the amount of blowby entering into the carb is not changed in anyway over the stock carb system. The stock 72-74 and later European carburated systems already dumped the gases into the carb intake just the same as mine. The small amount of extra fresh air going through the crankcase is effectively metered by the carb, just like any other air.

I like this system because it provides good fresh air flow through the crankcase at high RPM/full throttle operation, exactly when a system depend on manifold vacuum won't.

For anyone wanting to copy this system, the air flow from the fan shroud must be metered through a small orifice or you will blow oil out through the breather and other places as well.

Wed Nov 25, 2009 1:53 pm

Sounds similar to the late model stock T3 engine, except it fed air into the rocker area of the heads from the air cleaner. Excess case gases then got sucked into the intake.

Trammy is in here now, he can 'splain it better :)

Wed Nov 25, 2009 4:57 pm

Wildthings wrote: If you do have bad seals or gaskets this would NOT be the way to go.

Thanx for the input....I don't plan on running the fan air into the case, if anything, I may vent the valve covers. I have replaced every seal and gasket on this road trip. Most recently the dizzy o-ring that I really didn't notice as much of a leaker until I placed some vacuum in the case (1st test without the pushpin regulator)...the howling it made was soooo obvious. 8)

I believe the case mating surface was the last source of the seeping (it needs some dental floss)...and I can't fix that at the Motel6. :wink:

I drove another 60 miles today, after re-adjusting the choke, and all seems well. Tomorrow I am headed into CA for some turkey, about a 400 mile round trip, so that will be a real test.

It's only been 2 days, but the bottom of the case is still dry, and there are still no overnight oil stains on the pavement... :)

Fri Feb 19, 2010 4:53 pm

Heads up

I just realized that if the breather diaphram perforates outside the center area where it seals the incoming vacuum, that pressure would push the center of the diaphram closed. This would cause pressure to build up and push oil out the engine. The oil breather would only leak vacuum if the center of the diaphram broke. All the pressure would have to go out the small hole on the bottom and the tiny hole on the top. If you went to test it at idle it might show open because there was little pressure but out on the highway underload the blowby could be strong enough to close the opening off.

The arrows show the blowby gasses flow. If that diaphragm perforated anywhere except the center, increased pressure under load would push the diapgram down on the center because the area above the diaphragm is closed off to the outside except for that tiny hole.

Sat Feb 20, 2010 4:59 pm

SGKent wrote: Heads up

I just realized that if the breather diaphram perforates outside the center area where it seals the incoming vacuum, that pressure would push the center of the diaphram closed. This would cause pressure to build up and push oil out the engine. The oil breather would only leak vacuum if the center of the diaphram broke. All the pressure would have to go out the small hole on the bottom and the tiny hole on the top. If you went to test it at idle it might show open because there was little pressure but out on the highway underload the blowby could be strong enough to close the opening off.

The arrows show the blowby gasses flow. If that diaphragm perforated anywhere except the center, increased pressure under load would push the diapgram down on the center because the area above the diaphragm is closed off to the outside except for that tiny hole.

In general I don't think that this is a typical problem. The diagrams usually fall completely apart. I have though seen a Vanagon WBXer unit that only failed on the outside but not in the middle, sealing off the vent.

Fri Feb 26, 2010 10:11 pm

I accidently came across an Audi thread tonight that looks like the same device but it is attached differently. The part number is 06A-129-101-F and it is known as a pressure regulating valve. Most likely I will buy one and have someone like Whip618 machine me a base for it that will sit on the stock breather baffle. It would be cheap to have a plate made with a tube welded to it, and a piece of hose then fit one of these that are still sold.

Fri Feb 26, 2010 10:17 pm

Picked up several similar valves a year or so ago. Haven't gotten around to trying to use one of them yet. Let us know how your set up works.

Sat Feb 27, 2010 12:27 am

Wildthings wrote: Picked up several similar valves a year or so ago. Haven't gotten around to trying to use one of them yet. Let us know how your set up works.

Your inline filter breather circuit is a critical part, how is that filter working?
Colin

Sat Feb 27, 2010 1:11 am

Wildthings - our bus is in a smog state so it has to be close to original or we would vent into a catch can like yours. Worse case we would meter into the plenum through a standard PCV valve and then let air draw through the rocker covers from the air cleaner. That would keep the case close to ambient too. Then adjust the AFM to compensate.

Sat Feb 27, 2010 7:16 am

Changed my set up from drawing into the intake to having the exhaust suck it all out, seems to work good.

Sat Feb 27, 2010 9:39 am

Amskeptic wrote: Wildthings wrote: Picked up several similar valves a year or so ago. Haven't gotten around to trying to use one of them yet. Let us know how your set up works.

Your inline filter breather circuit is a critical part, how is that filter working?
Colin

Colin, If you are referring to the system I have on my carburated bus where I take air off the fan shroud, filter it and run it through an orifice before dumping it into the crankcase, it works well and has for years. Never tried that particular system with a FI engine though, in that case it would be introducing some unmetered air after the AFM so it might negatively affect the idle and emissions. At this point I couldn't recommend it for a FI application, I think that Ray Greenwood's system would likely be preferable on a FI engine.

Sat Feb 27, 2010 12:02 pm

Wildthings wrote: Amskeptic wrote: Wildthings wrote: Picked up several similar valves a year or so ago. Haven't gotten around to trying to use one of them yet. Let us know how your set up works.

Your inline filter breather circuit is a critical part, how is that filter working?
Colin

Colin, If you are referring to the system I have on my carburated bus where I take air off the fan shroud, filter it and run it through an orifice before dumping it into the crankcase, it works well and has for years. Never tried that particular system with a FI engine though, in that case it would be introducing some unmetered air after the AFM so it might negatively affect the idle and emissions. At this point I couldn't recommend it for a FI application, I think that Ray Greenwood's system would likely be preferable on a FI engine.

Yes...thats correct. The system I am speaking of is the exact system that 411/412 with D-jet uses. The problem with using it on L-jet is that is does bypass the AFM...so it gets no fuel metered for it.
Since D-jet has its metering unit (MPS) attached to the plenum where the stock 411/412 oil/crankcase/PVC breather dumps to.....that metering unit can be simply adjusted to compensate at idle...and also compensate at higher rpms.

I can't really think of a perfect way to use that same system on either L-jet or Carbs...not saying it won't work adequately....just not as well as it does with D-jet.....because with D-jet it operates at high vacuum. With L-jet and carbs....just dumping the breather box back into the upstream aircleaner operates at very low vacuum.

It appears that the diaphram used on the later bus and 412's actually is a method of modulating the crankcase exhaust so it has a constant level of low vacuum (like was discussed here already). It really is a way to limit the volume coming out of the crankcase at any one time so that it does not upset the overall fuel mixture.

However.....venting rocker gases straight to the plenum downstream of the AFM (like the 411/412 with D-jet)...CAN work....but I think controlling it may be difficult. In this case...with L-jet....enrichment would happen because any break in the vacuum of the manifold by lareg amounts of crankcase gases....might cause the fuel pressure regulator to spike. Just some thoughts. Ray

Tue May 11, 2010 10:57 am

SGKent wrote: Heads up

I just realized that if the breather diaphram perforates outside the center area where it seals the incoming vacuum, that pressure would push the center of the diaphram closed. This would cause pressure to build up and push oil out the engine. The oil breather would only leak vacuum if the center of the diaphram broke. All the pressure would have to go out the small hole on the bottom and the tiny hole on the top. If you went to test it at idle it might show open because there was little pressure but out on the highway underload the blowby could be strong enough to close the opening off.

The arrows show the blowby gasses flow. If that diaphragm perforated anywhere except the center, increased pressure under load would push the diapgram down on the center because the area above the diaphragm is closed off to the outside except for that tiny hole.

Did you get a chance to install the new one yet? :D