Rocker Cover to Carby hose? what is it?

Hi all,
could someone please explain what the hose is for that runs between the rocker cover and carby please?
It also comes in from the side of the engine also and meets in a "T" at the top of the rocker cover.
It is on top of a straight 6 vauxhall motor in a Bedford CDJ

thanks
Wacker

RE: hose is for

Probly earl eye anti pollution laws
suks the fumes from under rocker cover into carby for recyclin

But
WaddaEyeKno
LOL
cya

Swishy is right. It is for Positive Crankcase Ventilation. The idea is to drag the oil vapors into the inlet so they get burnt rather than vented straight out to atmosphere.
It was part of the early polution control gear. I am not sure when it came in but my 1965 Ute doesn't have it.

Thanks guys.. does this mean it isn't essential for good engine running? I'm waiting on a replacement part for the hoses on top, so at the moment it is just open to fresh air. No dramas with anything like dust getting into rocker cover?

My 1955 International Truck and XP ute both vent straight to atmosphere. I don't know where the pipe to the carby ends up. If it goes into the throttle body above the jets my expectation is that it will run but a fraction lean as there are no oil fumes to burn.

Not being an engineer nor a mechanic I have no experience to fall back on but have been told that pollution gear, if fitted, must be operational for a vehicle to be roadworthy so be careful if you are driving it down the road in this condition. I don't think it is a safety issue but it is a legal requirement according to what I have been told by ny brother-in-law when he put his XB then F250 on the road. In both cases the pollution gear had been disconnected before he bought them and he had to reconnect it for the roadworthy.

Depends where the hose connects at the carby.
If it's below the throttle plate, it will be pulling a vacuum on overrun and as such there may be a PCV valve at the rocker cover.
Running with that system open to atmosphere will cause the carby to suck in dust etc, run lean and idle high.

If the hose connects above the throttle plate it's simply a crankcase vent, so no vacuum and only dust into the rocker cover to contend with.

I think you will find almost everything post 60 had positive crank case venting of some sort, most vehicles had it long before that. (Chevrolet had it from the 1930's, even the Willys Jeeps had it after 1943)

Most times the hose goes into its own fitting in the intake manifold or into the side of the air cleaner but some have the fitting just under the carby. Early ones were just a straight pipe but most had a crude Positive Crankcase (PCV) valve normally just a ball on a spring in the pipe. As stated above it can draw from both rocker box and sump or just one or the other. Naturally side-valve flat head engines only need a sump vent but some even had a vent on the tappet cover side plate.

This is why oil filler caps/breathers all had an oiled wired mesh filter - not to catch the oil going out but to catch the dust going in via the air being drawn through the engine by the crankcase ventilation system.

Nothing to do with air pollution in the early days but an attempt to keep the engine clean externally from mist out of breathers and the walls inside the lower block clean also by reducing oil mist congealing on the sump walls as the engine cooled after shut-off. Also there is a very slight chance of a perfect explosive mix occuring in the sump, particularly if too much choke is used and this is sucked out.

Of course now the PCV system is a vital part of the entire anti-pollution arrangements on all modern engines.

Lang

reminds me of the early '70's when Datsun's had an air pump to purge the unburnt gasses from the exhaust, the vanes inside would lock up and a new pump was very expensive, I would take the pump apart, throw away the vanes, reassemble the pump and it would last forever, save the man some money, no emission test in those days but looked correct.