TheSamba.com :: View topic

Tue Jul 15, 2008 7:59 pm

to do list

Wed Jul 16, 2008 8:07 am

WHAT!! The tower diaphragm is spring loaded OPEN!

In that event, I don’t see how that tower vent could ever operate as intended. Do you suppose it likely that the firm building those towers put the springs in wrong, and VW never dissected one to check? Why should they? And there seems no other way to check them. Maybe that answers the mystery. That design could never be expected to operate correctly from intake boot vacuum. The lack of an offside diaphragm vent would tend to confirm the intended operation was as in my previous post.

James

Wed Jul 16, 2008 8:40 am

You would think, and if it were that way it might work like you had sensibly theorised, but there's no way that spring would have fitted above the diaphragm. The diaphragm is flat and very close to the lid, and even if new and supple couldn't extend more than 1/2" from the lid underside. The spring when fully compressed is deeper than that. There's also a seat around the base of the J-tube where the spring rides. So I think they are built as designed. The question is, why are they designed that way?

Or maybe the question is, why did they port it in before the butterfly? If it was after the butterfly, right into the plenum, it would work the way that is described in the pages Dog posted: valve would be pulled closed by the high vacuum at idle and mid-throttle cruise, allowing only the tiny flow thru the orifice at the bottom of the J-tube; valve would pop open to allow more venting volume at WOT, when blowby is the greatest. Maybe the tower got designed right, but someone else dropped the ball on applying it (that's pretty far-fetched, but stranger things have happened). At any rate, the explanation of its function in the manual is perfectly opposite to what it would actually do.

Wed Jul 16, 2008 10:04 am

Very true tencentlife, the tower valve most certainly does not, and cannot, operate as described in the company manual pages we have seen on this thread.

Maybe the original thinking was as you suggest, and then other concerns caused a change of heart, after the towers were already contracted for. As I recall, 1984 was a tough time for all auto builders as they scrambled to adapt the new environmental rules. The Rube Goldberg appearance on the water boxers does suggest that a scramble was underway, and in such an environment one might expect adjustments to the original plans. All our attempts to understand the mystery surrounding this valve are likely to be in vain, without inside VW knowledge, by someone who was there. All we know for certain is that it does not work as advertised.

That said, I wonder about the member who claims that a new breather tower solved his poor idle problems. My only guess in that case, is that perhaps he had a leaking hose all along and corrected that leak in the process of changing the tower. Out of interest I just went our and clamped the tower hose closed on my own Westy, while the engine was at idle. As expected, there was no noticeable change in the idle behavior or RPM. But with all this interest, I have ordered a new tower just so I can look inside the old one. After reading your postings, that exercise is really not necessary, for I now know what is in there. I will have a look anyway though, out of interest.

Regards,
James

Wed Jul 16, 2008 10:44 am

I went to the auto parts store yesterday looking to buy a new one myself, but after reading the latest posts I am very happy they not have any and were not able to order one. Probably would have been $100 wasted.

Squeezing the hose off does nothing, another hose in the area did occasionally lower the idle speed when squeezed shut, but doesn't have the same effect now.

I did discover that I had forgotten to reconnect the O2 sensor, and hooked it up again. That made quite a difference. Now it will idle at around 800 rpm and occasionally when warm will surge to 1200 before settling down.

Sounds like tencent has a solution. Hoping he can come up with something marketable to keep my van running and clean . . .

Wed Jul 16, 2008 11:22 pm

I cut an old breather tower apart today, it was off of a 1.9L with an unknown history. The diaphragm was almost totally missing. Only a small circle in the center remained, which was deformed from being suck down into the closed position. I did appear to still be sealing, which made me think that the failure mode might be for it to block the flow when it is supposed to be open. With most of the diaphragm missing or even when it is just holed crankcase pressure would act to hold the diaphragm down against the outlet pipe, instead for forcing it away. No telling what affect this might have on your idle and oil use.

Without cutting them apart I also tested two other breathers I had lying around by sealing the bottom with the palm of my hand and then sucking on the outlet tube. Both appeared to have holed diaphragms as neither held vacuum. One was off of a '91 so about as new as you can get for an original part.

I was going to go for it and order a new breather from VW, but someone cut through the main feed line and we didn't have phone service all afternoon. :x

Not being able to order a new part, I did decide to do a little experimenting with the old one. Since the engine in my 84 is pretty ratty with high oil use I decided to drill a drain hole in the bottom of the outlet elbow inside the breather tower so that any oil that gets past the diaphragm would have a better chance of draining back into the engine. I chose a 5/64 bit and went at it. I was surprise to find that even this small of a hole made a noticeable change in my idle. It is the best it has been since I was in Mexico over last Christmas and the engine started running crappy at idle and lost bottom end performance. This change makes me think that a failing breather may have been the cause of my poor idle.

Thu Jul 17, 2008 6:36 am

But there's already a hole at the bottom of the elbow. That's the specified idle orifice. You can see it in the pic I posted. Maybe yours was completely blocked with crud.

I guess if the hole was blocked and the diaphragm torn, case pressure would push the diaphragm down onto the top of the J-tube, but with the hole there I don't think that would happen. What had your spring done, just shoved its way past the remaining circle of diaphragm?

When you sealed it off and were still able to draw air in at least proved one thing, I think: there is some venting above the diaphragm, however small. I couldn't find any vent provision there in my inspection, but if it were sealed the diaphragm wouldn't ever move downward, as there would be no pressure differential and the spring is pushing it up.

Curiouser and curiouser, said Alice.

Thu Jul 17, 2008 7:39 am

Well blow me down! I would have guessed the chances of a diaphragm failing as you describe - that is, with the remaining bit of rubber somehow getting past the spring and plugging the outlet pipe – to be most unlikely. Was the spring still present?

Drilling another hole in the outlet pipe seems superfluous to me. What was wrong with the original idle orifice drilling? Was it perhaps clogged up with oil and dirt? Was it possible that the entire outlet pipe was somewhat clogged with dirt, oil and rubber remains from the perished diaphragm?

What did you actually do with the old tower after observing the plugged outlet pipe and drilling a hole? Did you put the pieces back together with epoxy resin, or temporarily duct tape them, or what?

Thu Jul 17, 2008 8:55 am

Quote: Well blow me down! I would have guessed the chances of a diaphragm failing as you describe - that is, with the remaining bit of rubber somehow getting past the spring and plugging the outlet pipe – to be most unlikely. Was the spring still present?

Yes the spring was still present, but for one it doesn't exert a whole lot of force and two the remainer of the diaphragm and the built up crud formed kind of a cap.

Quote:
Drilling another hole in the outlet pipe seems superfluous to me. What was wrong with the original idle orifice drilling?

I hadn't realized that there was an orifice, so I didn't look for one in the breather I cut open. That breather was so caked with crud that it is likely that any hole that was there was plugged. I will examine it and see.

The breather I actually drilled was on my 83 1/2, which as I said uses a lot of oil. I don't know if the hole was present on that one or not. Kind of hard to see, even though this particular breather was pretty clean. Can't see it if you don't look anyway.

Quote: I think: there is some venting above the diaphragm, however small. I couldn't find any vent provision there in my inspection, but if it were sealed the diaphragm wouldn't ever move downward, as there would be no pressure differential and the spring is pushing it up.

There is a hole, it is under the cap on the left side. On one of the three breathers I inspected the hole was totally blocked. The other two past air.

Thu Jul 17, 2008 9:07 am

I never could find a hole anywhere above the diaphragm on any of the ones I have. I looked very closely.

Yes, the spring is very weak as I mentioned earlier. But there still needs to be a pretty good vacuum force to pull that diaphragm down.

Thu Jul 17, 2008 10:03 am

From what I understand Wildthing, the breather you drilled (and which seems to improve your engine idle) is one which looks clean, but never has been opened. You therefore don’t know what the diaphragm condition is, but we might suspect that perhaps it too has rotted, and in fact I also wonder whether that outlet pipe may be also clogged………except for the hole you drilled. It would seem reasonable to expect that such a clogged up breather would not only cause engine idle problems, but also cause case pressure buildup during higher engine operation. Do you have oil leakage from that engine? It would certainly seem likely

Moreover, the issue of sludge blockage in the outlet pipe seems more and more likely to me. With the almost certain deterioration and rotting of those original diaphragms after all these years, added to the oil vapors and sludge buildup – it does seem likely that at least partial blockage may be present in more old, original towers. In such a case your engine case will have been venting itself also past the dipstick seal, valve cover seals, crankshaft seals and so forth.

This would not explain why the earlier member reported that his engine idle problems were solved by a new breather tower, for he also reported that the engine idle smoothed out when he removed the hose and plugged the intake boot completely. That one still sounds like an air leak. If one wishes to check whether the case is breathing through the tower or not, go out and take off the oil filler cap with the engine at idle. That will introduce an air leak large enough to lean out the engine to a rough, rough idle. It probably will die. A lesser air leak, such as an old, hard or split hose between the tower and rubber boot will have a similar effect, just smaller in scale.

I would still expect that the more common failure mode would be as tencentlife discovered in his dissected example.

Thu Jul 17, 2008 12:03 pm

tencentlife wrote: I never could find a hole anywhere above the diaphragm on any of the ones I have. I looked very closely.

The hole is there, but very hard to see, it is on the underneath side of the cap and tiny, may 1/16 inch. I would not have noticed it if I had not cut the one breather open and saw the slot that moves the air around the edge of the diaphragm to the lower side of the cap. On the one that was clogged it was not visible at all, I had to clean the breather carefully and use a dental pick to find the hole. I suspect that when the diaphragm goes bad then oil passes up through the diaphragm and out the breather hole. This might account for some breather towers being covered with oil, and it also likely causes the bleed hole in others to become clogged.

Quote: From what I understand Wildthing, the breather you drilled (and which seems to improve your engine idle) is one which looks clean, but never has been opened. You therefore don’t know what the diaphragm condition is, but we might suspect that perhaps it too has rotted, and in fact I also wonder whether that outlet pipe may be also clogged………except for the hole you drilled.

I do know that it is holed, because it failed my suction test. How badly is another matter. The oil use on my 83 1/2 engine has always been high since I purchased it, about a quart every 5-700 miles. At the same time as I started having idle problems in Mexico last winter the oil use doubled to a quart every 250-350 miles. I suspect that the idle and oil use are tied together. Assuming I soon acquire a new breather it will be interesting to see what happens to both.

I looked again at the breather that I had cut apart and there was no visible drain hole or orifice in the outlet pipe elbow. After a good cleaning I spotted it and opened it up. Remember that this breather was very full of crud, but other breathers might have clogged drain orifices as well which might account of poor running and higher than normal oil use. As I said I know nothing of the history of the engine this breather came off of. The guy at the local yard asked me if I wanted the engine and I said yes, a gift horse not to be questioned.

Thu Jul 17, 2008 12:19 pm

Some more thought on how the breather is supposed to operate. Above the diaphragm there should be atmospheric pressure. From below most of the area of the diaphragm is subjected to crankcase pressure. Ignoring the spring for the moment, the valve will be closed when the pressure in the crankcase is below atmospheric and open when it is above. This would keep the crankcase pressure from dropping too low and sucking air in around the various engine gaskets and seals. The spring just changes the operating pressure differential a little, meaning that it is okay for the crankcase to operate at a slight vacuum, but not much of one. I think the orifice is there mainly to drain oil back into the engine, but would tend to moderate the open and closing of the valve somewhat. It is pretty small, in the order of 1/16-5/64 inch, I haven't actually measured it.

When the diaphragm fails then the valve probably often stays fully open causing a low crankcase vacuum, sucking in air and drawing out oil. This might also alternate with the center little circle of the diaphragm closing and staying closed, shutting off the flow of air into the intake air stream and causing high crankcase pressure. As I see it a bad diaphragm could cause it to idle rich at some points and lean at others, alternately jumping from one condition to the other.

Thu Jul 17, 2008 4:29 pm

This has been interesting, if nothing else. Before stumbling on this thread, I had always considered that tower to be nothing but a baffle, and now it has me baffled. Like looking at a bottle of moonshine……….you don’t know what’s in there….. But, you know for certain that it is not what the company claims it to be!

I just received a new breather tower from Van Café (along with the Famous Amos cookies).

Yes indeed, a vent opening (square shaped) is clearly present under the left side lip of the upper tower. It occurred to me that if I suck and blow into this little vent it should be possible to create either vacuum or positive pressure inside the upper diaphragm chamber, and thus cause the valve to close and open. It works and requires surprising little pressure to close that valve. If I blow gently into the square vent, I can feel the diaphragm immediately close off and I can no longer blow into the vent. This is just what one would expect, only the pressure required is surprisingly little. But guess what? If I suck on that vent hole and create a vacuum, I can sense the valve open and I then can hear air rushing in from the lower tower (large) chamber. Somehow the vent hole communicates with the main chamber under open valve conditions. Probably there is a simple flap somewhere on the diaphragm to accomplish this. I hope my old tower will answer the question when I cut it open. Doubtful though, as it is the original and probably little remains. In any event, this is the ONLY way I know of at present to test whether the damper is intact and operating without cutting the thing apart.

I will report any findings.

James

Thu Jul 17, 2008 6:05 pm

How much did the breather cost through Van Cafe? It list for $106 at VWOA and wholesales for $89.

If you do get flow through the vent hole under the cap when you blow into it and this is normal, then my little suction test wouldn't work. :cry:

Thu Jul 17, 2008 6:21 pm

I ordered one today from the local VW dealer.

$97 canadian./ 96.67 US

Thu Jul 17, 2008 7:00 pm

No flow when you blow in positive pressure Wildthing. It immediately seats the seal and there is no more flow. The flow through is when I pulled a vacuum at the vent hole. Then the valve opens and there is flow through.
The Van Cafe' price was 88.5 plus 9.46 shipping.

Thu Jul 17, 2008 7:26 pm

but what happens when you suck on the vent that connects to the throttle body assembly? does it close the valve?

Thu Jul 17, 2008 8:06 pm

Gordy, yes it does.........provided you close off the tower base end and thus create a vacuum in the main chamber (Otherwise you are simply pulling a limited volume of air through without a change in pressure). As a test though, this method is not so good, because all you have to confirm the valves closing is that you can faintly feel the action taking place at that end of the tower.

The other method of applying positive pressure to the upside of the diaphragm is more satisfying, a more positive test; because if the diaphram were unsound there would be flowthrough. With a good tower unit, you are blowing into a closed chamber, and there is no doubt of the result.

Thu Jul 17, 2008 9:59 pm

Too bad new ones cost so much, I would like to dissect a new one and see what they are supposed to look like inside. Any one feeling rich?