Jaguar series ii breathing

Hello All,
I am wondering about how the crankcase "breaths" on the 6 cylinder? I fully understand PCV both open and closed versions and I am aware of the breather apparatus on the front of the engine but my question is two-fold. First, does aforesaid breather draw or expel air into the air cleaner? Secondly, where else is air admitted or expelled from the engine?

Greg in Montana

The breather should be connected by a pipe from the front of the engine to both carbs. In theory, during certain operating conditions the depression in the carb bodies provides suction to draw off the crank case pressure. Never sure how well it really works, not as "positive" as a PCV system.

You should find an elbow fitted to the air cleaner back plate (in the middle) between the carbs...just to ad to what Jesse wrote.

Gentlemen,
Thanks for the reply on my engine breathing. The question remains....Where is the intake for the air being drawn off the front breather? I have never had an American engine apart that did not provide both and intake and low pressure exhaust for crankcase fumes.

Greg in Montana

The older XK engine had a housing on the front of the head that had a flexible hose going down and attched to body or frame. The housing had a filter to stop drops of oil, and the crankcase vented thru this hose. The XJ engine ( newer XK ) has the same type housing and vent but attaches to the air cleaner and pulls crankcase fumes back thru engine for reburn thru cylinder firing. Filter still collects drops and must be cleaned occasionally. Just as the domestic PCV pulls vacuum from block and re-enters the air thru the mainfold for reburn, but does not have filter and pcv must be cleaned or replaced at manufactures intevals.

Thanks for additional information Larry. I guess I am laboring this question, either "laboring" or no one knows the answer? Any engine I have had apart (many) have a way for the engine crankcase to "breath". Air is drawn in from somewhere and out somehow. With either the "roaddraft-tube" or the PCV system, air has to be admitted someplace. Is it possible the Series II engine is equipped with only a low pressure "draw" of vapors with no allowance for fresh air to come in?

Greg in Montana

I know what you are asking. Early examples, steel wool mesh in oil fill cap to clean inlet air, road draught tube "baloney" cut to increase suction at speed.
Early PCV systems, same steel wool mesh in oil fill cap, but orifice controlled manifold vacuum replaced road draught tube.

Now, on Jags....
They did away with road draught tubes (or catch tanks), and now use inlet suction (not much) before the carburettors to remove fumes.
Since they haven't got a lot of flow, no need to have a "source" of fresh air on the other side.
Whatever crankcase pressure is built up immediately vents into the air cleaner plenum.
Smart?
No.
Works?
Yes.

Just make sure every 20-30K you pull the screen out at the front of the cylinder head and clean it, more often on clapped out engines.

Dave

The internal air you are looking for comes from the by-pass of piston, etc. Engine is an actual air pump and the rings do not keep it all in, nor do the valve seals and etc. With the volume of air these engines pump, it comes out in the sump and thru the breather systems, or PCV system in domestic cars.

Thank ou Dave and Larry. Now I understand the Jag engines do not allow for "intake" air for crankcase ventilation, only drawn off exhaust fumes. I fitted my breather (on the front of the engine) with lawn mower type air filter and did away with the tube to the air cleaner. I wonder if that is sufficient breathing for the crankcase? Thoughts please,
Greg in Montana

Well......you are going to have some issues, for sure.
There was one of these Brit Car Shows on a while back....where they "flip" a car...Jag....smoked like Hades.....the screen in the vent assembly on the front of the cylinder head was plugged (or, so the made-for-TV-storyline tells us).
Removed, cleaned, all good.
There is a reason engines use screen or coarse mesh steel wool, and not just to keep critters out of the crankcase.
If you use a lawnmower type filter inside....foam or paper...it is going to plug solid, if it hasn't already.....and crankcase pressure from blowby, guides, whatever....you'll be popping seals, gaskets, o-rings, it ain't gonna be pretty.

Not long if it gets caught on the timing chain and throws the thing into dishevel. The air cleaner is the vacuum for the crankcase to clean it out. If this is not there as TOC said it will blow gaskets and etc. I've been working on these Jags since I was 15 yrs. old some 47 yrs. ago and this is not the way you want to blow an engine.

Gentlemen... Thank You all for the responses. I have done away with the breather filter I affixed externally to the crankcase breather. I now run a tube to one of the air filters. Hopefully that will be sufficient. I shall monitor the screen withing the original breather apparatis.


Greg in Montana