Oil bath air cleaners

Discussion in 'Mech Tech' started by scrooge95, Oct 22, 2017.

  1. So it's been brought to my attention on a different thread of mine, that the big black monster that lurks in the dark right hand recesses of the engine bay, isn't functioning as it should.
    Apparently when I stuck on the pipe that leads from the inlet manifold just below the carb, to the top of the oil bath, I should generate the kind of vacuum pressure that will stick my tongue to the pipe. Instead, I can just continually keep drawing in nice oily flavoured air.
    I've had a look and the pipe is good, so it's somewhere inside the top of the oil bath that trouble is brewing.
    The pipe that leads from the other spigot on the top, down to what I now know to be the actuator, does result in a nice bit of tongue-sticking vacuum pressure... so at least I know vaguely my enemy and where it lurks.
    Any ideas, oh great brain of TLB?
    I know mostly we have forsaken our oil baths for shiny young things that sit, sparkling directly on top of twin carbs etc, but I'm an old fashioned kind of girl and I do like a good bit of 'stock'!

    The workings of the top part of the oil bath don't seem particularly accessible, but this is what I can see of the bit what is not doing it's job, when I have a look in through the big pipe that goes to the top of the carb.....

    Its not a brilliant picture, but hopefully it shows what it should.

    Anyone know if this is right, or should there be other bits in there too.?
    If I put my thumb over the end of that bit that is visible, and suck on the tube thingie, there's still no vacuum.

    Right, that's quite enough sucking for one post, do your thing TLB :thumbsup:

    1974 Type 1 1776cc engine, older style oil bath, single solex carb.

    Thanks in advance.
    Merlin Cat likes this.
  2. The bit that should be working there is a valve that connects the two spigots to each other to pass vacuum until it reaches about 30 deg C then it snaps shut.

    The intent of this design is as follows.

    If it is below 30 deg C at the top of the air cleaner:

    At idle or low throttle the manifold air pressure is sucked lower by the engine running. The little valve lets the vacuum through and the hot air flap is pulled open. The air leaving the carburettor is cooled as it expands into the vacuum of the manifold.
    The hot air entering the top of the carb is cooled by ?20 or 30 degrees by this expansion . Because it started off hot it is now just room temperature.
    So when you put your foot down, you get much less fuel condensing out.
    If the air gets too hot at the top of the air cleaner, above 30 C, the little valve shuts and so the air flap drops down and the cleaner is fed cold air until it cools down enough.

    But as you put your foot down, the manifold vacuum is reduced as the throttle plate opens. The hot air flap drops closed. Cold air comes into the engine because the engine is more efficient with cold air coming in. But the carburettor is not producing such a drop in air pressure so the air leaving it into the manifold is still around ambient temperature. So still no fuel condensing out.

    The heat risers work all the time to boil off any pesky petrol puddles. When this is all set up and you wrapped between the heat risers and the horizontal part of the manifold with insulating asbestos:eek: lagging you got this : http://www.clubvw.org.au/antarctic-vws

    However as you have an air leak there , you need a new valve in the top of the air cleaner. And these are apparently £60 new as fitted to early VW Golfs and our air cleaners.
    Or try talking to Megabug as they had second hand cleaners at Volksworld for £10, or go to the e.g. Slough swapmeet, or ask me to get you one for under £20 while I am there.
    Or even @Davidofts hoard may contain such items.
  3. What is the pipe from the manifold actually connected to? Have you got something that looks vaguely like this in your air filter?

  4. Interesting!!!!
    I have an Australian oil bath with a crankcase breather pipe that connects to the oil filler box and a vacuum pipe connected to the Rubber Tee petrol breather / expansion pipes [​IMG]sorry cruddy old pic

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  5. Dare I ask what that actually is??
    I had limited time to have a look this afternoon unfortunately, and I couldn't get the top part of the air cleaner off in situ as there is a pesky clip right round the back. It's a lot easier to take the whole thing out and separate it - but time was not on my side. I'll see if I can have a look after work tomorrow, but if I remember correctly from the last time it was all out and apart for a clean and an oil refresh, the top part is all hidden away and inaccessible, other than by peering in through the big 'ole.

    I guess my valve is not performing.
    @davidoft do you have such a thing as a perfectly performing old oil bath in the parts emporium per chance?
  6. It's the thermostatic vacuum valve that your manifold pipe should be connected to. Two pipes, one in from the manifold, one out to the actuator.
    nicktuft, paradox and scrooge95 like this.
  7. Ah, so there should be something like that in there. I'm gonna have to get it out and have a look aren't I?
    To be honest, even if it's there, I think it's probably broken so the question becomes....
    Is it a 'user serviceable part'?
    Can I actually get to it to replace it?
    And if the answer to the previous two questions is Yes, then where do I get a replacement?
    Humph. Thanks @snotty and @mikedjames
  8. davidoft

    davidoft Sponsor

    I could have, I’ll look
    scrooge95 likes this.
  9. You are ;)

    Might be broken, might not be connected. Still available as a spare, easy to fit.
    scrooge95 likes this.
  10. I suppose there is still a bit of daylight left......... :rolleyes:
  11. Fit a light in the engine bay at the next Techenders

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  12. Go on, do it!
    paradox likes this.
  13. Oh yeah!

    Merlin Cat likes this.
  14. So!
    This bit is a sealed unit?
    And the way to get to the thermostat is.......?
    And even if I get it out.......?
  15. Somewhat related to this. Ours as the oil bath air cleaner with the metal looking thermostat on the side. It has no spigot for a line from the fuel tank breathers. Is this correct for a bus? How is it supposed to work?

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  16. Hmmm, the bit that goes to the tank breathers / t-piece on mine is the rubber bit on the bottom half that is sticking out towards the engine (pointing upwards on my top picture up there ^^^)
    Is that the same as on your Aussie one @paul2590 ?
  17. I don't suppose you know, Mr @snotty Sir, which of the bits is 'in' from the manifold and 'out' to the actuator on this picture do you? The spigot above the interestingly technical LHS in your picture, or the spigot above the flat RHS in the picture? Just asking coz apparently if I connect mine up the other way round to what they was, I can get my tongue to stick to the pipe.
  18. Yep! Same principle

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  19. scrooge95 and snotty like this.
  20. I honestly can't remember! I'll have a look at my old paper airbox a bit later.
    scrooge95 likes this.

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