Does the pipe vent to atmosphere or feed back into the carb?

My MK II was aquired without an engine so I am restoring her blindly with no visible points of reference save the service manual and moss motors exploded diagrams - but they only show isolated parts of the puzzle.

Any help appreciated.

 

It feeds into the bottom of the intake plenum just at the edge of where the filter canister hose fits. My plenums has an attachment point for it.

 

Sorry, the app doesn't let me edit. I'm thinking of the S type of course.

 

There's a point to attach the flexible to the aluminium inlet system between the air cleaner and the carbs. If you are not using the original system, it's OK to vent to atmosphere preferably some place where the pressure may be on the (slightly) low side.

 

Ahhh... about that.

 

Might put a pretty K&N Filter on the end and let it dangle then?

 

Don't put a filter on the end of it, it'll **** up the engine, just let it vent if you're going to do that.

 

No point in filtering an outlet?

 

only to act as a catch can, but as others have said - I won’t.

 

Didn't the original Mk2 have an oil catch can arrangement that this breather hose sat in rather than allowing the oil to drip onto the road under the car?

 

Catch cans are widely available from impressive ones in stainless down to old fruit juice bottles.

 

Is it ok to fit a PCV valve between the head breather and the carburettor manifold

 

You could, but why? You still need a (or the existing) connection to the inlet system between the air filter and the throttles. Addition of a PCV is something else to go wrong and even when it's working it increases the possibility oil and dirt accumulating on the back of the inlet valves. PCVs were introduced mainly to eliminate blow by gases escaping the crankcase and reaching the atmosphere when an engine is under high load. Given the way most of our cars are used, it doesn't really seem worth the effort. It's better to ensure the original breather isn't blocked and possibly add a small catch can to it to collect oil.

 

The 3.8 has a round filter casing with an aluminium section below, the breather on the front of the head connects to this.

 

Mine has pancake filters, so I can’t do this

 

Our engines have what Jaguar called a breather that allows blow by gases to go into the inlet system air flow between the air cleaner and the carbs. If you add a PCV valve, it has to be in another separate pipe that takes crankcase gas from a different part (preferably opposite end) of the engine from the breather and carries it to the inlet manifold downstream of the throttles. When the throttles are open and inlet pressure isn't too low, the PCV valve is open. Air flows into the engine through the breather (the opposite of our cars) and crankcase gas goes through the PCV valve into the inlet to be burnt by the engine. When the throttles are closed, the PCV valve closes; if it remained open, it would lean the idle and low load mixture in an uncontrolled way. Under these circumstances, the flow in the breather line is blow by gas out of the engine much as in our cars.

There are two main points. First, adding a PCV valve entails adding an extra pipe from somewhere like the back of the engine. The second is that all it might offer is some potential improvement in crankcase ventilation under load.

If you don't have anywhere between the air cleaner and carb to connect the breather (and flow is always out from the engine as in no PCV), take the breather pipe via a catch tank to to some location under the car where (you think) the pressure in the slip stream of the car might be low. For me, some sort of catch can is always preferable to letting oil that passes the gauze separator going through the engine to be burnt.