MGB woes....

Like you were suggesting, this sounds to me like crankcase pressure pushing oil down the valve guides. Try temporarily removing the oil filler cap and see if that helps.

The only problem with that is it would only take a minute or two before the engine compartment would be covered in oil. There is definitely pressure and a steady pulsing of oil fumes coming out of the filler anytime I take it off when the engine is running.

bill

Agreed about the mess. Your problem sounds like a blocked breather somewhere. Can't help with the US spec directly but UK spec cars (mine) sometimes get blocked breather hoses that give these sort of symptoms.

John

Is it possible that the carbon canisters have become clogged with gunk from 87K miles of filtering oil fumes from this self same crankcase?

Looks like I know what I'll be doing this weekend. I'll let people know if I find this to be the case so others can profit from my problem.

All the best.

bill

You should be able to tell if there is a difference very quickly this way, if it makes no odds then you've ruled out lots of possible causes. I took my v8 for a trip up the hill and back, didn't see much oil (it's got plenty of oil around there anyway, though, not exactly concours.)

The way this works, the gap between the pistons and the cylinder walls isn't entirely air tight, especially if the rings are worn or broken. Detonating gas will "blow by" the piston into the crankcase particularly when working hard.

This pressure goes through to the head area (areas on my v8) where I have pushrods and you probably have an overhead camshaft, which may mean more oil sploshing about than me. At the end of the head is a sort of small tin can arrangement, on mine it is like it is filled with brillo pads. Oil sticks to the wire, drips back into the head (if not in too much of a draught!) and drains back into the engine sump.

The gas passes along a rubber tube and into the air filter (mine has a pancake). I can tell mines working because quite a lot of oil comes through and deposits on the filter, if that happened to be clean, I'd think "not breathing".

If the tube or tin can is blocked up with oil sludge the gas has nowhere to go and builds up in the crankcase. It also builds up pressure in the cylinder head and one of the escape routes is down the valve stems into the inlet tracts where there is a nice induction vacuum sucking on the end to aid the pressure blowing down the other. This carries oil, intended to lubricate the valve stems, in greater quantities than you want and burns it in the cylinders, producing oil smoke. This is generally ok because the guides and stems need lubrication and the oil can only go from there into the cylinder, where it will help to seal the piston rings against the walls. But you don't want too much going through there.

It'll do it more when working hard because the vacuum below and pressure above will be higher. Also, the oil and gas going into the breather tube can exceed the throughput it can manage, meaning a sudden build up in pressure once this limit is reached, but once the pressure is off, the oil trapped in the valve can return back to the drainage, reducing the hindrance on gas flow through the breather system.

Also, when the breather is working, some oil is bound to end up passing through to the carb where it will be swallowed by the engine and burned. If there is a lot of blowby gas, it will mean a lot of oil burning in this way as well.

(Additionally, in case this is significant in your engine, and for completeness, there is supposed to be a design on my engine that provides positive ventilation, which I haven't got now. The idea of this, the breather tube connects to the carb itself and is put under vacuum pressure drawing air from the crankcase rather than merely permitting it to exhaust itself under its own positive pressure. To go with this, the other head has a small tube with a fresh air inlet filter which supposedly lets air into the crankcase / heads to replace that which is drawn out by the breather.

(The idea of this is to deliberately suck out petrol vapours (which blowby gas includes) and burn them instead of letting them contaminate the oil, reducing its effectiveness and promoting engine damage. A clue that the breather is blocked, is when the fresh air filter is clogged up with oil and is blown off the tube to let the gas out there instead of sucking air in.)

BTW, if your engine has positive crankcase ventilation, removing the filler cap should mean air is sucked into the head rather than blowing out.

My engine was definitely not breathing properly, some time back, so I took off the filler and tried it like that, made a major difference. So since my breather was welded to the head, I got another head and new breather with tube, made all the difference in the world. I was being restricted to about 4800 rpm and pumped out smoke after a short period of full throttle on the motorway, all that vanished with the new breather (I actually added two breathers, but that would be a different story anyway.)

Hope this makes sense and gives pointers where to look, my eight pot is not the same as yours so I don't know exactly what to suggest. If you are worried about the oil, you could make some sort of coke can packed with brillo pads and holes cut in the top, I dunno, I wasn't too bothered because my engine leaks oil anyway and it wasn't too obvious that it was significantly more, if it actually was (might well have been saving oil since it stopped blowing it into the engine.)

You could also start off by changing the breather valves / tubing but if that's not the problem it will be money wasted. Still, it may be as simple as that and if the parts are cheap enough...

This is the valve guide seals, I had a midget that did the same thing after

Its head off and, spring compressor time. Not a hard job and while your there a good de-coke will make the job feel all nice and tidy.