L Jet vacuum leak pursuit '74 1.8, How does this work? Options

[wonkipop]

here you go @nihil44 .

why your remark about negative pressure made me think.'

the VW pure crankcase vent works this way.
on the L jet 412s and buses.

the membrane and spring inside is a 2 way valve that can respond to either crankcase vacuum (neg crankcase pressure) or alternatively intake vacuum the same way.
restricts or even closes off fume chimney from crankcase.

i can't remember all the combos for engine crank vac v positive pressure in relation to intake vacuum, high low and almost none.
all has to do with engine at idle, or engine under hard revs or engine at high rev cruise etc.

the valve is designed to respond to all those conditions.

-----

now -- there is just the oil cap version on the 914 to see if there is indeed anything to that and its not just a straight up cap with seals to the oil filler tube.

but you were right with your hunch. crankcase vac when it happens is involved.
its not always positive pressure. and van is right. because sometimes it is positive pressure. but the pin hole aint a pressure relief valve. at least for the VW version which i can understand. but not ours yet.

[wonkipop]

ok @nihil44

i had a good look at this over lunch.

i noticed the cap has a little hole in the side where the lateral springs join.

this does not vent straight through into the very interior of the cap (ie the crankcase chimney - instead it opens into a hollow body. the bottom section of the cap assembly is a hollow body tube.

i reckon we have a pcv valve exactly like the ones on the other VW type 4 L jets.
its incorporated into the filler cap itself and a grip ring is added to that to assist getting the cap off.

i drew a cross section of how i think it works more or less.

it cannot be taken apart easily, probably destroy the cap. and be be buggered if i am going to do that as i know you cannot get one of these in australia nor probably find one at a junk yard to cut open and do an autopsy on.





i can't remember where i read that there is no pcv valve on a 1.8.
maybe i was imagining it.
but if i did read that somewhere i reckon it is wrong.
there is one? its built into the top of the filler cap?

the weird spring

i've stared at that spring for years trying to figure out why its there.
some sort of grip on the filler tube?
shrugged my shoulders at it.

it hit me today.
its the flame arrestor for a backfire.


more useless research provoked by your smoke machine teapot simulation?

[nihil44]

@wonkipop

Man that is some dissertation on the filler cap! Thanks for the cross section diagram. That is the way I thought it would be and I agree that I am not going sacrifice a cap just for dissection purposes or purchase one from USA. Hardly any 914 parts available in Aus.
I received another bunch of parts today from 914rubber via Fedex and commented at at the time that the amount I have spent on trans Pacific carriage of parts could probably purchase a couple of business class fares to Europe

It all makes sense. I too wondered about the function of the spring inside the cap and the flame arrestor explanation also makes sense.

Nice work!

David

[wonkipop]

@wonkipop

Man that is some dissertation on the filler cap! Thanks for the cross section diagram. That is the way I thought it would be and I agree that I am not going sacrifice a cap just for dissection purposes or purchase one from USA. Hardly any 914 parts available in Aus.
I received another bunch of parts today from 914rubber via Fedex and commented at at the time that the amount I have spent on trans Pacific carriage of parts could probably purchase a couple of business class fares to Europe

It all makes sense. I too wondered about the function of the spring inside the cap and the flame arrestor explanation also makes sense.

Nice work!

David

most of it is not a dissertation.
just thinking out loud on the way to the last post.
the last post is the succinct summary of prior ramblings and dismissal of my own errant thought projections.

its your fault.
you sent me off on a tangent.
can't stop until i get to the end.
blame it on my post graduate training in the USA.
its their fault as well.

i was talking to my mate max tonight on the phone after diinner.
he said that mgs had these types of oil caps and were round in australia.
said they were famous for turning into chimneys.

never mucked around with an mg and never will.
but ...... if we knew some mg guys they probably could have told us about this.

@djway is right on the money.
you should not be able to blow smoke out of that pinhole.

[Van B]

well it's a good thing those caps are NLA...
I suppose I better start searching for one of those too. I know for sure mine vents on occasion when the engine is cold.

[wonkipop]

well it's a good thing those caps are NLA...
I suppose I better start searching for one of those too. I know for sure mine vents on occasion when the engine is cold.

you can't get the bus version of it either.

and if you look through that samba thread its pretty clear that at this point in time 99% of those bus ones are kaput. but the engines are still running.

........not much you can do about it?

except maybe rig up a new pcv valve set up external to the existing one and somehow gut the cap and seal the pinhole there?

the cap pcv looks to be a delicate thing to balance crankcase pressure to intake vacuum so its a draw very closely matched to whatever blow by there is.
since there is no other way inlet air is drawn in to the system unlike the d jet cars with their vented heads? you would always want a slight draw from the crankcase i think,
just to help the oil return down the pushrod tubes. but it all must be very slight as you don't want any significant unmetered volumes of air - although i would have to think hard about that and give myself a headache as that air has in a round-about way gone through the afm already. so its kind of a balance of losses?

it does look like its designed to fail wide open - unless you got unlucky and somehow remnant diaphram blocked the channels to the engine intake line.

------

i could be wrong but i think i have seen images where potentially they kept on using that central diaphram part for later golfs and passats in the second half of 70s. probably NLA for those too. but a possibility would be to see if they can be gotten hold of.
then a disassembly operation done where you insert that cap piece with diaphram into our oil cap assembly if they can fit together. its really only the diaphram bonded to upper cap that is needed.

i would only be willing to do it with another second hand 914 cap and see if its possible to take it apart without destroying it. and if so is there a diaphram part you can then fit into it and then i guess glue it all back together with the spring positioned in it. with care it must be a possibility that it can be taken apart the same way it was assembled in the first place.

[wonkipop]

well it's a good thing those caps are NLA...
I suppose I better start searching for one of those too. I know for sure mine vents on occasion when the engine is cold.

@Van B and @nihil44 .

i think i have satisfied myself what the original valve does.
its not so much a positive pressure relief valve -
its more an excessive vacuum control valve.
its there to stop over strong vacuum situations where inlet vacuum might be high enough to cause too much suction -----> leading to sucking in the valve cover gasket as people like to talk about happening? meant to stop that?

i'm guessing that the typical high vacuum situations on the inboard side of the throttle plate are not the problem as the high vacuum is in the intake plenum but not the intake boot (ie idle or de-accleration) - but perhaps it can happen at cruise - part throttle which is a high vacuum situation where the vacuum is also in the intake boot (also operates the advance can in the distributor in that situation but no other).

with no membrane this control would be lost in that situation.

a lot of the rest of the time i don't think there is so much vacuum getting through to that valve. sure its strong vacuum at idle but that is inboard of the throttle valve and this connection is outboard of that. and at full throttle there is not a lot or no vacuum really, its pretty atmospheric.

most of the time its going to want to be open. except at cruise/part throttle?
then it might want to be very restricted or almost closed. could also be sucking oil up the crankcase vent pipe at times like that too.

i mentioned the mg smokestack behaviour above.
it must be very prevalent in the southern hemisphere.
you can buy a rebuild diaphram for them!
check it out from this heritage mob in new zealand.
(a very similar dimension to the 1.8 cap - 75mm).
https://www.classiccarparts.co.nz/index.php...product_id=1421

led me to ebay and numerous rebuild diaphrams for all sorts of later model vws. must be a whole cottage industry of folks rebuilding their pcv valves.

https://www.ebay.co.uk/itm/283483223754

some of them look similar to the diaphram inside the bus unit from the 70s.
which i assume is what it is like inside ours.

might have to go in search of a second hand filler cap for a 914 and ship one in.
doesn't matter if its kaput.
then go test the water with these various diaphrams if i can get it apart.
i believe if i were to retain the original spring in the one we have, there is a chance you might be able to rebuild the pcv.

i've fixed up bosch 3 port fuel pumps when they are supposed to be unfixable sealed units. it is probably worth a hack at this.

i'll be smoke testing the one i have when i get the car in the workshop.
i can't feel any puffing through it, but you never know.

edit

here are some more promising leads much closer to the mark.
need some diameters.


https://www.rkxtech.com/blogs/news/replacin...valve-diaphragm

https://www.rkxtech.com/collections/pcv-val...alve-repair-kit

[Van B]

@wonkipop
I did some part number tracing (because you’ve pulled me into this vortex of obscure oil cap research) and the only 914 to ever use this cap was the US/CAL 1.8L

All other models, including the AN engined Europe 1.8L used the standard cap. What they had instead is the PCV in the little black box that the filler neck bolts too.

So, rather than trying to repair NLA parts, why couldn’t We just seal the cap (or buy a sealed cap) and then find a parts store PCV that can be put inline on the hose that runs between the fill neck and the intake boot?

[wonkipop]

@wonkipop
I did some part number tracing (because you’ve pulled me into this vortex of obscure oil cap research) and the only 914 to ever use this cap was the US/CAL 1.8L

All other models, including the AN engined Europe 1.8L used the standard cap. What they had instead is the PCV in the little black box that the filler neck bolts too.

So, rather than trying to repair NLA parts, why couldn’t We just seal the cap (or buy a sealed cap) and then find a parts store PCV that can be put inline on the hose that runs between the fill neck and the intake boot?

we probably could.
but first i have to stop referring to it as a positive crankcase vent valve.
it is a PRV valve - in the L jets. Pressure regulating Valve. there is a difference.
works the opposite way to a typical pcv in the D jets.
they are trying to pull air through and they inject air to do that. they can.
we can't. its more about balancing the pressure in the crankcase in ours.
back and forth. and never letting the vacuum draw from the crankcase become too strong because it will go looking for that air at the weakest point.
kind of the opposite of too much pressure and blowing the seals and oil out.

so we have to have the right valve.
which is what i think most modern valves are.
more or less the same way of working as the L jet ones.

the question would be matching the valve to the engine.
working with the spring in the way that the cap valve does with its spring.

------

correct - the AN twin carb engines have the same valve as the D jets.
though i don't think they have vented heads. thats a d jet thing i believe.

you are right, the one on ours is only on the EC L jet engine.
something like 15,000 - 20,000 engines at most.
chickenfeed to VW.

------

just started mine to do the puff test.
could not discern anything holding my palm over it.
all i could feel was air current being pulled into fan making it difficult to know what might be going on anyway.

did yours noticeably puff?

used my finger to plug the pin hole - nothing happened. idle or revs did not change.

watched the vid nihil44 was talking about. pretty neat smoke machine. will have to make one its so good.

----
only thing about a replacement in line versus original is the spring strength in relation to vacuum. the way i was thinking of it only the membrane gets replaced. and you know it works because you have retained the original spring. these things are a kind of universal design for a lot of cars but suspect they are tuned through spring strength?

[Van B]

Alright my Ozzy friends,
I tested my oil cap today. I wrapped the side/throat (around the spring) in electrical tape real snug and put vacuum on the center bore using a rubber cup that came with my mighty vac. It was tricky to get the cup to sit well enough that I could pull vacuum, but once I got it, I was able to pull 25 in hg. It would leak down, but not faster than I could build vac. I think the leak was from the imperfect sealing. But regardless, the pinhole on top is definitely there to allow the diaphragm to move.
If I blew into it, no air came out the pinhole.
When you release vacuum, you will feel a small puff that is from the diaphragm spring pushing it back, but nothing else.

I guess I was imagining things when I thought I felt air coming through it…

[Van B]

Also, the PN on my cap is 022 115 303, not the PN from the pats manual of 022 115 309. I can’t even find a picture of the -309 part on the interwebs.
FWIW, -303A is the type 4 breather the VW L-jet engines got.

[wonkipop]

Alright my Ozzy friends,
I tested my oil cap today. I wrapped the side/throat (around the spring) in electrical tape real snug and put vacuum on the center bore using a rubber cup that came with my mighty vac. It was tricky to get the cup to sit well enough that I could pull vacuum, but once I got it, I was able to pull 25 in hg. It would leak down, but not faster than I could build vac. I think the leak was from the imperfect sealing. But regardless, the pinhole on top is definitely there to allow the diaphragm to move.
If I blew into it, no air came out the pinhole.
When you release vacuum, you will feel a small puff that is from the diaphragm spring pushing it back, but nothing else.

I guess I was imagining things when I thought I felt air coming through it…

good stuff.

fair chance mine is ok too then.

been up country picking grapes at my uncles beef farm (with small vineyard).
took the big citroen.
my only problem was holding it under our ridiculous speed limits - 110 kph. (IMG:style_emoticons/default/sad.gif)
the cit just wants to run, 140-150. (IMG:style_emoticons/default/smile.gif)
almost as much fun to drive as the 914.......almost.
corners flat, no body roll - hydraulic suspension.
(there is one in the car chase in the film Ronin - takes a hammering getting rounded up by a big audi).

on way back today dropped in at workshop.

told mike about prv hidden in the oil cap.
he hadn't picked it either and he is a mechanic. he thought it would be down in the baffle somehow and hadn't bothered to look or think twice.
---said there is a mob in queensland he has in his contacts that repairs vacuum diaphram valves - if they have metal casings. eg, the decel valve i have found, if its not good.
but have to be metal vacuum valves.

however......if need be they may well have been a possible source for a new membrane.
we would just need to get (a potentially sacrificial) cap apart to explore the option.

------

@Emerygt350 sent me a pm with some photos of his fox body mustang he just had to break out and take for a spin in winter. i love it.
ford styling of that era is just right in my book.

(IMG:style_emoticons/default/beerchug.gif)

so.....here is some falcon shots for him.
its been keeping me away from pulling the 914 into the shop.
i'm nearly finished. got the prep and paint for the tub to go.
i have learnt body work on this poor victim.
replaced areas indicated in images. and anything painted black por15 in tub. which amounted to a lot of the car (in a key dicey structural area).
aussie cars do rust. did not get galvanised bodies until near the end of car manufacture here. this is a 94.
not going for over-restored with this one. its meant to go on as a functional work horse.
so we kept its lifetime accumulation of battle scars as much as we could and just went the rust. plenty of that!!! the interior is amazing. usually aus cars are like desert cars in usa - cracked dashboards, fried vinyl, brittle plastic hell. but this one has a showroom interior astonishingly. think it spent too much time parked under trees in the shade getting shat on by parrots which probably caused half the rust.

didn't do the paint. skills in that department extend as far as picking up a brush and applying Por15.

[emerygt350]

Man that is such a cool looking cruck. I think you mentioned before but I forgot: Is it the 2.3? What did they put in it?

[wonkipop]

Man that is such a cool looking cruck. I think you mentioned before but I forgot: Is it the 2.3? What did they put in it?

4.0 L straight 6. just under 200hp. overhead cam, EFI.
pretty simple engine.

manual or auto trans. this one has the auto.

[emerygt350]

Oh yeah, that sounds like a great motor. Was it multiport fuel injected?

[wonkipop]

Oh yeah, that sounds like a great motor. Was it multiport fuel injected?

yes

pretty much like this.

as per ford 80s/90s engineering department conventions, when they went to the cross flow head they left the distributor where it was in prior version of engine and its buried under the inlet manifold. (IMG:style_emoticons/default/sad.gif)



this model (the XG) had the EFI.
the model before which looks identical apart from a different grille piece and some minor interior details still had the carb.
best bit is you can still get all the parts, ubiquitous. ......and cheap.
unlike 914s with L jet. (IMG:style_emoticons/default/smile.gif)

[emerygt350]

That thing is just begging for a turbo....

[wonkipop]

That thing is just begging for a turbo....

https://www.tiperformance.com.au/products/e...conversion-kit/

might need a traction control unit to go with it? -
given the utes had problems at roundabouts in the wet unloaded.