I dunno, but I thought all 1098/1275's had #70 on the intake manifold:

Don't know what #70 refers to. Intake is a Pierce.

I think #70 is a pcv valve that was fit to the original SU manifold. I have no idea where it is supposed to enter into the crankcase.

#70 is for a stock manifold...so, now you have to figure out how to do something similar with your manifold...if there's nothing wrong inside the engine, this might be the problem...where you're hooking up your hoses that should do what #70 did.....does that make sense?

Tony, where is yours going to be hooked if there is no timing chain cover vent? How did these things create crankcase vacuum?

Well I'm pretty confused. Surely someone has put a Pierce intake with Weber onto an early 1098 before? Maybe even more reason for me to get the SUs back on there! I don't think that whole PCV was ever on this 1098cg, later versions only perhaps?
BTW
Thanks again for all the patient input, great community here. The experience and advice making the whole MG adventure much more fun.

If I have the story straight. The vacuum from intake going to rocker cover drew during idle/high vacuum situation, the vent tube poked down into the slipstream to get a little vacuum at speed. That's it. Maybe I just need to tap into the intake, put a port on it for the rocker cover tube instead of having it go into the air cleaner where it "shares" the vacuum with all the other air coming into the carb.?

Going thru the same problems no vent on the timing cover. Someone has added a vent off the dip stick tube and rocker cover when you hook up # 70 pcv to both vents it pulls oil into the exhaust but she doesn't leak but smokes. So I hooked up one of these and stopped smoking.

http://www.pbase.com/rsrock/oil_catch_can

Lots off stuff on the web about this and it works well no more smoke and no more leaks.

Mark

Tony I could have saved you some money, I pretty much throw everything in parts drawing in the garbage can I have never liked the idea of pulling crankcase pressure thru my carbs, it's pressure, give it a path it will find it's way out.

Details?
Where exactly in the system did you put it?

Tony,
Originally the 948’s and early 1098cc (some cg's) did not have item #70. It wasn’t until the front cover “can” as added that they ran that valve.
The metal tube on your rocker cover shown in picture post #492415 would have simply gone over to the front tube sticking out of your air cleaner housing. 100% the same manor as a 948cc engine was. Once the front cover vent was added the remaining stock of rocker covers that had the tube receive a rounded end with a very small hole in the end. They then eliminated the tube all together

Dug

Hap, I understand your point about pressure, but if you can create a vacuum then you can slow the egress of oil around the rear scroll seal.

To answer everybody's question about what I'm gonna do:



I couldn't've explained it better...thanks, Dug.....I've got the air fliter can with the tube for the vent hose to attach to...got the valve cover....&, if you remember Hap, my intake had no holes for vacuum.

This subject has been covered many times before.
No, a hose to the air filter is not a pcv.
The idea of a pcv is to give POSITIVE crankcase ventalation.
That is, to actively remove air from the crankcase.
Allowing the air to vent into the air filter is not actively removing air.
Actively removing crankcase air is to allow a vacuum supply (restricted) access to the crankcase.
And then provide a restricted air inlet to the crankcase to create a flow-through system with slight negative crankcase pressure. This helps stop rear main bearing dribble.

I took the liberty of modifying your engine picture, placing the pcv valve where it should be.

Then after doing all that drawing on my portable pc with no mouse, I found another source describing the whole thing.

http://www.vicwhit.com/spitfire/spittech.html

P.S. I like your double heater valves.

We don't use crankcase vaccum on the race cars, just give them plenty of places to breath, and the crankcase pressures on the race cars due to the rpms involves is way greater than that on a street car. The main reason for crankcase vaccum thru the carbs was it was eco-friendly, or thought to be, if your engine is sealed good, then nothing much other than air is coming from there anyway. The engine is a big ole pump, it doesn't need vaccum to evacuate, just a path.

Donn - good explanation & great link...that may solve the problem...this thread now gets 5 stars!!

That's what I was thinking in post #492497. Thanks.
I did it this morning. Can't report much yet on effect on oil. Car runs different, as expected, hopefully I can tweak it without a rejet. Pulled the line off the intake and it had oil in it.
PS
Oh, and I didn't put in a PCV valve yet, just a "metered orifice" approach, the hole on the intake fitting is tiny, 1/8" or so.

My old Opel Rekord had a metered orifice. It worked ok. I think the hole was a little smaller than 1/8". The good old Chevy, Ford or Dodge pcv valves are really quite nice. I think it was Ford who had a threaded unit, which would screw right into a tapped hole in the manifold. I wish I could get one of those valves over here. The others fit into rubber grommets suitable for a valve cover. I think a certain Chevy unit could be put inline.

My Opel GT had a metered orifice too. PO had plugged the opening at the valve cover, it had oil leaks. I put it to rights, it helped. It was quite a bit smaller than 1/8", probably closer to 1/16"
The guy with the Spitfire in the above link tried a valve but it was too restrictive, I went straight to a small opening. At the moment all I did was snip the end off a vacuum cap, put it over the barbed fitting and clamp the hose over it all. Not very sophisticated but I can change the size easy enough to play with it.
I just got back from a run, not far, 5 miles maybe. Enough to get it all warm.
No oil from drain tube. Maybe a bit yet from the dipstick but it's the wrong tube and fitment is poor, or its still residual oil from the total oil soaking it got Thursday.

In other news:
Besides tapping the Pierce for the vacuum fitting I redid the manifold gasket to address an exhaust leak.
So, on this latest run: no oil drips (dropped off my son at a friends and though I only idled in the drive for 5 seconds: no drips on the guy's perfect driveway!) no decel backfires (exhaust leak) decent brakes and smooth running.
never better, good morning's work.

WHOO-HOO!!