UPDATED: Need help help finding a NOS part.

[SGKent]

Have been trying to find one of these for sometime now and just not having any luck. The subject comes up here from time to time and workarounds or used ones are usually the suggested solution. I tried cleaning out a non-leaking used one but it leaked afterwards so I surmise that most of the used ones that don't leak are being held together by baked on carbon and once cleaned the diaphram will leak. On a 1975 to 1978 FI bus they limit the maximum vacuum inside the crankcase to prevent excessive wear of the rings and valve guides as well as limit oil consumption. Eventually ever FI bus will need a new one to run right if it is in a smog state with a visual test.

Is there anyone who might have a line on someone who has NOS parts that might have one or more of these? Or does anyone have connections to Mann Hummel where we might get them to make some? I had a contact tonight from a Vanagon owner trying to find the Vanagon version and they are equally in a bind. This is especially true in smog test states where there is a visual inspection. If you know where there are new ones please contact me. I would really like to get Mann Hummel to make some new ones for Samba owners because every 75-78 FI bus is going to need one of these and the diaphrams were never designed to last 30 years. I have written them twice with not even the courtsey of an answer. The only other alternative is if there is an automotive engineer in the group who has access to tables where we might be able to substitute another style readially available PCV valve in the line to take the place of this one.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

here is an article about the same desighn device on an MG / MGB. Looks like Mann Hummel took a British design and modified it. The main difference is that the British ones come apart and have replaceable diaphrams.

http://mgaguru.com/mgtech/engine/cv103.htm
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[PARTSBUS]

i will check this weekend.

[fusername]

I do belive certain styles unscrew, possibly porsche. if they could be rebuilt and repurposed?

now here is my thought, take the valve, mush it up so it flows 100%, then add a modern PCV valve, looks like a brake one way valve in line between the old valve and the S boot or whever it is going. you loose the simple beauty of the stock one which keeps oil condesnation in the case, now it is in the line, not a huge deal. just a cure for those with personal problems, not for those trying to pass inspection. I have also heard of folks replacing the spring based diaphram valve with a flapper valve, but that is a bit more complicted.

as far as nos goes, I have no idea where one could come up with that.
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[79,78 bay bus]

i have one if you are still looking
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[reluctantartist]

One thing that would be cool is to make something out of aluminum that could use the MG diaphragm or the like so you would have something that is serviceable.
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1982 Westy, 1974 412 Variant... Yes, Aircooled's are great! Oh and I do have modern computer controlled vehicles too, but I just don't care about them.

[raygreenwood]

The problem with replacing or ommitting that diaphram is mainly in how they opted to vent the crankcase. The L-jet bus type 4 engine...as compared to the D-jet type 4 engine....have radically different crankcase venting. The 411/412 and 914 use a flow through....much much much more effective.
It keeps the crankcase at a low to moderate level of vacuum all the time except when rpm is high with a wide throttle opening...and therfore with lowered and almost atmospheric pressure vacuum. It uses a normal style PCV valve....which actually is a major hindrance for D-jet. Many people find that replacing the PCV with a constant bleed small orifice works wonders for tunability.

The difference is type 4's with D-jet have a crankcase to plenum connection that supplies high vacuum.

One person pointed out a good piece of research a while back...about the fact that the bus diaphram unit....was designed to keep the crankcase balanced at near atmospheric pressure....which also seems to be of little benefit....just that they designed it that way. But suffice to say...since the L-jet bus version connects its PCV/oil chimney diaphram to teh S boot...vacuum is incredibly low...or no....so a delicately balanced diaphram and flap valve is used to be able to act with that low vacuum...and vent the case.

This is not saying that the low vacuum system of the L-jet bus is better than the high vacuum of D-jet at all.....just that they worked with what they designed. Its also much less effective than D-jet at keeping the case and oil clean or scavenging gasses.....but it does work adequately.

One of the major (if not main reason) reasons why they do NOT use a direct plenum PCV valve hook-up on L-jet...is the same reason why the regular PCV disturbs D-jet. When the PCV valve pops open at certain throttle settings....on D-jet....it causes movemnt of the diaphram in the MPS. That causes enrichment. A fixed orifice of small size actually allows constant controlled verting...and can be compensated for in the MPS adjustment.
On teh bus...with L-jet....you have a vacuum variable fuel pressure regulator. If you had a normal PCV valve with normal levels of manifold vacuum....every time it kicked open at certain throttle settings....it would tweek the fuel pressure regulator.


Switching to a normal PCV valve would be a problem for L-jet. It could be easily gotten around though with an adjustable aftermarket fuel pressure regulator. Ray

[reluctantartist]

Ray, if I understand you correctly you are saying that we would need to not only replace the pcv system, but the fuel pressure regulator to make this work correctly? Does that mean those of us operating with busted PCV's are causing problems with the fuel pressure regulator as we drive since the open pcv would be effecting the fuel pressure regulator?

Thanks
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1982 Westy, 1974 412 Variant... Yes, Aircooled's are great! Oh and I do have modern computer controlled vehicles too, but I just don't care about them.

[Bleyseng]

What about using the Ljet PVC oil filler setup off 1.8 Ljet 914 motors. I think those are still available new.... I'll poke around for some.
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76 Porsche 914 2.1L L20c, 120hp Djet (sold)
87 Syncro Westy Titan Red 2.1L 2 knob 100k miles

[WhirledTraveller]

[raygreenwood]

Its a possibility.

If you are going to a regular PCV valve (which I would actually go to a fixed orifice not an actual moving flap or spring valve).....you will require better vacuum than what you generate upstream of the TB in the S-boot.

So....let me first explain how it was done on the 411/412/914 with D-jet....and what problems the PCV valve caused.....and how simple they are to fix....and then I'll note how we cross that over to a bus with L-jet.

On a 411/41/914...it starts at the air cleaner.

Air is PULLED/SUCKED...from the air cleaner (filtered)....through a 12mm hose.....through a splitter that doubles as a flame trap (mounted on the fan housing)......and split into two 12mm hoses.....one running to each head/rocker box.

This clean cool air....is pulled through the rocker box.....through the pushrod tubes.....through the crankcase.....through the Z-baffel cast into the type 4 case under the chimney....through the excellent oil baffel inside of the oil breather......through the PCV valve mounted in the oil breather....into the fuel injection center manifold or plenum.

So....the engine intake manifold supplies the vacuum....and its a pull through system from the air cleaner.

The problem is that the PCV valve opens generally because of EITHER crankcase pressure or vacuum....actually a combination of both. But....D-jet has an MPS (manifold pressure sensor) that controls load enrichment. It's vacuum connection is roughly 1" from where the PCV hose dumps into the center intake manifold.
Since the ECU has no control over when and how much that PCV valve opens....you get this untimed, out of control pulse that disturbs the MPS sensor. The better and tighter your engine is tuned...the more you notice the issue.

Its the untimed pulsing of the opening of the PCV valve that is the issue. Now...if we propped it open so it would not pulse...but just flow a stable amount of air...there is no pulsing...and no issue. We can make a minor adjustment to both idle and to the MPS. Its really simply...nearly the equivalent to replacing your TB with one that is 1-2mm larger in diameter. Just make an adjustment in idle and air volume and you are back to normal..but without that pulsing.

Now...cut to your bus with L-jet and a proper PCV system like this one. That same minor pulsing of the vacuum signature "might" disturb the vacuum signature from the manifold on your fuel pressure regulator....giving rich spikes.

You might be able to get around this simply by careful sizing of a fixed orifice for the PCV and careful placement of the of where the hose inlet into the plenum is.

But for proper PCV..you realy need more vacuum than what the S-boot generates the way your system is set up now.
This is why they designed a system with a diaphram instteda of a spring loaded plunger. The smaller the vacuum level...the larger the diaphram area you have to have...for the vacuum to multiply against. If you used a normal spring loaded plunger PCV on your system now...the small vacuum generated in the S boot would not even budge even the weakest PCV spring. Ray

[SGKent]

I wrote Mann Hummel again and pray they answer.

Here is the problem. Right now most states don't smog back to 1975-78. If they do they don't verify the PCV. With new laws coming on smog and a push for higher mileage, my guess is that the US Gov't will try to push every old car off the road that they can - except for maybe parades etc. From special interests view, each new car sold saves fuel and funds GMAC/Chrysler etc. Do you see where this is going when you need a PCV valve that is non-existant or your car ends up not passing smog? The current simple non-smog solution of plumbing to a breather catch can and then venting to the atmosphere like early bugs will be an automatic fail smog. So either we find a way as a community to get Mann Hummel to make replacements, or we design one cheaply that will work.

Ray's solution of feeding vacuum through an orifice is kind of how Alfa Romeo solved their L-jet crankcase pressures however it too has problems after 30 years as you can see from these photos. It is an oil vapor separator (catch can) and has plumbing to feed the oil that condenses from the mist back to the crankcase. Next, a second pair of vents need to be added from the heads back to the airbox so clean air can be drawn at a semi-constant rate through the case, then the AFM has to be adjusted for that extra airflow. But it can be done cheaply out of PCV pipe at the hardware store and jbweld, and Ray has already worked out the orifice sizes. Even with this, in some states it would be not pass smog until the states' air boards approve the conversion.

The next most likely solution is something like this Pro-Vent crankcase pressure regulating valve, photo below. It is most commonly mounted on its side. One hose goes to the engine crankcase, one to the intake and the small one to the crankcase below the oil level or to a checkvalve that prevents it from draining back into the breather until the engine is off.

But to buy one and build the parts one would be looking at $250 per install which is too high considering a repro VW-Mann Hummel pressure valve might be $40 new and identical to what we have now.

Here is the Porsche version off a 1998 Boxster 2.5 that is about $100.

Those things said - at this time I am willing to pay $$ for a NOS valve if anyone has or finds one. Bob Hood found the last one and I missed it by 15 minutes so they are out there. He paid $60 for it so the price should be somewhere between $60 and $75 plus a $25 reward to whomever finds me one. I have used ones already and cannot get one apart without damaging it. If you can get a bad one apart without damaging the plastic, I will pay $10 for that one so I can experiement with it.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

Wow...cool pictures. Always worth it to see how others have done it.

Have you had any luck in looking at Watercooled VW versions of this? The diaphram unit in my 90 model cabrio was nearly identical except of teh mount.

Yeah..I agree with your sentiments. Until you find the exact way to (a) make it work right and (b) do it for a cost that is affordable, reliable and repeatable....best to stick with stock.

For years I spent money on replacment NOS 411/412 PCV valves until I figured out how to reliably make it work.
Problem about doing a D-ejt style fixed orifice PCV on an L-jet bus for a lot of folks....is that it will not pass the visual california inspection.

Its very clean for oil control though. As puiledriver notes...you can make it even cleaner than stock (oil control wise) by adding an extra element in teh chimmney area. Ray

[Vwman55]

How does the valve operate exactly? Pressure from the case opens it or increasing vacuum from the air intake? How do you test it?

[SGKent]

it works as follows on 75-78, maybe 79 too.

The unit bolts to the breather (right image). Air and blowby is drawn via the hose into the top of the unit. That suction passes through a 1/4" +/- nipple inside to the breather box which sits on top of the crankcase chimney. When the suction pulls too high of a vacuum in the crankcase the diaphram is pulled down and closes off that nipple. Then pressure builds in the crankcase and the diaphram releases until the vacuum builds again.

VW next changed the design of the chimney and added a tube so instead of bolting on, the valve plugged into the chimney (left image). Those valves are NLA also and hard to find NOS but they seem to be the same as the 75-78 except for the mounting. I have not tested them to see if the spring is different. Notice the differences below.

There are two ways to test. You can plug either opening with your thumb and suck on the other opening through a hose (device is oily). The device should hold a vacuum. If the diaphram is bad it will leak through the small top hole. Or, you can suck on the top small hole (bottom photo) and if it holds vacuum then the diaphram is good. The diaphram is the only part that is failure prone.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

following Bob Hood's suggestions on how to get these apart, I was able to get two apart wthout destroying them. There is a material difference in the insides. Whether that results in a different pressure I can't say. Someone with the later style needs to tell us where the vacuum source is.

If you wish to take one apart they are heat welded or glued together. I tried acetone and Berrymans on the glue remnants and it did nothing to soften the welding material. I used an xacto knife along the grove between the top and base to remove any extra glue. Then I used the stiff blade on a pocket knife to go around trying to pop the top loose until I found a weak spot. It took three or four trips around the top at an angle to spread the lifting load out until a weak spot revealed itself. Then once I had it started I was able to pop it off. In the photos you can see where the weld broke between the top and bottom.

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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

UPDATE - they both take about 2.2 to 2.3 oz to close the springs. The smaller spring compresses much more before it closes where as the bigger spring closes early in its travel. I would say the pressures would be similar. The diaphram appears to be is silicone rubber. I am not a plastics person but these are really simple and could be cheaply reproduced I think.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

did the math. someone back me up on it as it has been awhile.

Surface area of diaphram
1" radius x itself x 3.1416 = 3.1416 inch squared.
2.3 oz / 16 oz per pound = 0.14375 pound.
0.14375 pound x 3.1416 inch squared = .4516 pounds per sq inch

This would mean that the valve is designed to hold approximately - .5 psi in the crankcase which is for practical purposes ambient pressure.

Does the math look right?
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[SGKent]

I sealed the ones I have back up without glue and they hold a vacuum so they would do even better with a bead of JBweld or some other epoxy etc., or find a way to clamp them. I have submitted a request to a leading diaphram manufacturer in the automotive field to see what the minimum order and rough cost would be to make replacement diaphrams. If the cost is reasonable we may be able to rebuild our old valves.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[WhirledTraveller]

I think it is .14375 / 3.1416 inch = 0.046 psi

There was a thread a while back where someone tried to measure the force required to close the valve and couldn't measure it, it was too low. More or less the valve is holding the crankcase pressure at ambient.

It is a major breakthrough that you were able to take them apart without damaging them. The diaphragm looks very easy to reproduce, just cut one out of a sheet of rubber and glue it in.
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