I have a question regarding the crankcase breather systems that people add as an upgrade, as trying to get my head around such things. This may come across as complete rubbish, but its still a question in my mind that I still don`t quite understand.


See if you can get your head around my thinking?

Originally, on my oil filler neck, I had one of those stupid little 2" air filters, and after a decent run my engine would be absolutely caked in oil. What hadn`t run down the side of this filter would have escaped through the pushrod tubes and landed on the floor - the engine leaked like a sieve.


However, after a top tip on here, I connected a pipe from the filler neck to the carb air filter, which as I understand was enough to give a little bit of negative pressure and has cured ALL of the oil leaks as a result, which is absolutely brilliant.


However, I`m due to go twin carbs soon, so exploring options of how to retain the negative pressure here, if thats the right thing to call it.

Looking at a picture recently posted by Jazzy Early (knew you`d get the hang of pictures  ) of a fairly typical setup it got me thinking, as its a really clear picture of illustrating the breather system.



Obviously the tube from the oil filler is a positive pressure and as a side effect, will throw oil up into the small ally reservior, where it will syphon back to the heads when the engine is switched off. But the two pipes that presumably come from the valve covers, are these also positive or negative pressure as well.

If positive pressure, and oil also escapes through here and up into the reservior, I can theoretically see the return of my old oil leaks from the pushrod tubes due to the extra pressure, and I have seen many of these ally reserviors with those small air filter type breathers on them, presumably to reduce any pressure.

However, an open filter to the elements is surely only going to "neutralise" any pressure, unlike the connection to the carb air filter that actually "applied" a little bit of negative presssure if you see what I mean.

So either I have misunderstood this whole concept, or am I right in thinking that an extra pipe needs to go from the ally reservior to the carb air filter to give an even more efficient system?

Dave
they are well worth fitting as the problem you describe isnt the only thing it fixes.
The box pictured (I have a brand new kit surplus to requirements) has a foam filter under the lid and is designed to catch oil and let it run back under gravity.
I dont know where is +ve or -ve on this setup and in fact I think it varies depending on how you are driving, in reality there should not be any pressure build up of any consequence.

Imagine you are gunning it round a big roundabout, you are pumping oil into the left hand rocker cover while gravity + the pumping pressure is all that you have to get it back down the pushrod tubes to the sump, so clearly centrifugal force is holding against the rocker cover and it aint running back, also the sump oil has moved left and is probably trying to force its way up the tubes, the rocker cover is probably getting a bit of +ve pressure at this point. If you have a breather box fitted it wont go up the pipe to the box because of the height of the box and the fact it is near the centreline.

So you come off the roundabout and straighten up with your left hand rocker cover full of oil, without a breather this can only get back to the sump if air can get past it into the rocker cover, so could be quite slow, fit a breather and air gets in via the pipe and oil goes back to the sump.

Only downside is that air can get out of the rocker cover while driving in circles allowing sump oil to run up the pushrod tubes easier, so (IMHO) a deep sump is a requirement, although I had oil starvation without a breather box on roundabouts anyway.

I reckon they are well worth fitting, will PM you my phone number if this raises more questions than answers give me a bell

Dave

Hi Dave, let's go back to basics. When vw designed the beetle engine, they built in a small ventilation system into it. This is because oil and water do not mix, you end up getting emulsified oil inside your engine. When you run an engine, with the change of temperatures; you get condensation and water vapours forming; so if you do not get rid of this water vapour it messes up your oil.

VW's idea was to build into there engines a small air pump, to suck air into the engine and then let it out from the breather buy the oil filler. If you look at an original oil filler, you will see that it has an oil catchment area; to let the oil return when the engine stops or is ticking over. The breather then either exited from a pipe running down and out at the bottom of the engine or on later engines it was connected to the air filter boxes. Which  stopped them dripping oil everywhere ( the start of regulations). VW's little air pump is the spiral threaded bit on the bottom pulley.

So vw's idea works great until your engine starts to wear! Then every time your engine fires, more and more engine gases manage to get past the piston rings as they wear and it is these gases that pump through your engine, blowing oil and water vapours everywhere. If any fine filters are put on the breathers they will clog up with emulsified oil, which then pressurises the crankcases and makes them leak like yours did 

If you go for twin carbs, you can still connect a breather pipe to one of those. My personal opinion is that these fancy breather boxes are not needed on standard engines. Deep sumps are not needed either unless you are racing around or have bigger cc engines fitted.

So the bottom line is... when you get that other engine rebuilt and fitted, you shouldn't have so much oily air rushing out of your breather anyway 

Rob

This is a topic I have been interested in... OK so like Dave (DND) I had the little filter before too, and yes that side of the engines tin wear would get coated in oil from the breather filter.

Then Heritage insisted that I have some better form of breather kit on the engine (its reasonably spec'd 1776) - though I did query since the rocker covers they fit to the engine are rather nice Scat stainless steel ones, they have no option of porting for the breather pipes which is a bit crazy. Anyway, no problems I bought the breath kit (as pictured above) - I already have bolt on covers with porting from before anyway.

However just as I was about to fit it, Flags and Ollie (and others) suggested not to bother fitting it as it soon gets clogged up and you are forever cleaning it and in their opinion not that good overall. Instead, just port your oil filler breather to one of the carb filters (dual carbs).

Well, other have done the same and works well (including DaveDND) and to be honest, since I've done that too. Its spot on! 

I will hang onto my new untouched, breather box kit and bolt on covers for the time being just incase, there is a stronger case for them. (I do know others have them and they are fine) but so far the pipe to the carb filter is fine.

@Doon L001

I wasn`t aware that there was a foam filter at the top of those reserviors, but does clarify why the aftermarket made ally jobbies always have an extra filter on the top - I guess that they do the same thing. Yep, full understand what you have written, and no disagreements with the benfits of them as you describe.


@Farmer Rob

Brilliant description of the internal workings and design, but does kind of reinforce my thoughts.

Yes - I understand the "air pump" concept and the need to vent the water absorbed gasses to air.

Yes - I am in no doubt that my engine is FUBAR and is pumping more gasses than it should


But the question still remians though, rather than the air being pumped to the atmoshphere under its own pressure, does the addition of the pipe from the carb air filter, which will not only allow venting to the air as required, but also gives a little negative pressure meaning that the gasses can flow out of the engine even quicker ? Is this an extra benefit albeit miniscule ?

Hi Dave, I would say that the suck from the air filter is a good thing on a good engine but on an old engine, it could be blowing that much under load that pipe size could become an issue; so that the crankcase could still be slightly pressurised with the engine under load. The thing with an engine breather is that it has to let the engine breath but not build up pressure

If these breather boxes have a sponge filter in them, then I would remove it as it will only block and cause pressure issues.

Rob, surely if the blow from the engine is greater than the such from the carbs (which would be quite a feet) then the excess would be vented through the air filter on the carb.

Quote from: Roadrunner on August 21, 2013, 01:56:52 PM
Rob, surely if the blow from the engine is greater than the such from the carbs (which would be quite a feet) then the excess would be vented through the air filter on the carb.

Exactly, and by the same token, if the engine blow is of a very low pressure, surely a bit of suction from the carb would assist it?

I don't know who's engine this is but those valve covers really need swaping over so that the breather pipes run down the back of the engine. They're too easily pulled off or damaged where they are...

Quote from: Dave DND on August 21, 2013, 02:12:57 PM

Quote from: Roadrunner on August 21, 2013, 01:56:52 PM
Rob, surely if the blow from the engine is greater than the such from the carbs (which would be quite a feet) then the excess would be vented through the air filter on the carb.

Exactly, and by the same token, if the engine blow is of a very low pressure, surely a bit of suction from the carb would assist it?

As you said Dave, putting the pipe on yours to the carb has helped so evidence would say so.

And thats where the confusion kicks in . . . .

A lot of people upgrade to a crankcase style breather system as shown, which would suggest that over the years it has become a tried and tested method of doing things - (or simply that VW people are just sheep) - but I can`t help thinking that it could be very easily improved with another foot of pipe from the reservior box to the air filter

And if it really is that simple, why has no one else ever done it ?

Have seen these breather boxs mounted low Would defeat the point  was told mount as high as possible 
And single breather if mounted high on bulk head could solve your problem  For a bit of pipe*** worth a try













( *** but can only condone the use of overly shiny stainless braided parts and fittings any thing else could result in time on the naughty step )

Quote from: Dave DND on August 21, 2013, 03:03:59 PM(or simply that VW people are just sheep)

Got it in one!

IMHO the only type of breather worth having is the Berg type one (or the similar CB Performance or Das Resto one) that mounts where the original VW oil filler mounts and drains any residue straight back into the sump. 95% plus of street engines don't need breathers to the valve covers anyway.

Thanks David - that picture is pretty much the concept I had running through my head

when you look at how much air goes through the standard aircleaner intake there must be a depression in the air cleaner at high rpm simply putting your finger over the breather port with the motor running at speed will prove or disprove that fact.
pipes were returned to the cleaners for emissions control not because the manufacturers wanted to do it.
the problem is blow by in the motor pressurising the case due to the small size of the breather or restricting it with a fine filter.
the greater the volume/flow of the breather the less pressure is in the case to force oil out,  higher rpm use, bigger CC's and engine wear apply more blow by volume thus pressure if it cannot escape
The jas has a box breather fitted high up just because it was there, but no sponge inside it