One last try or I sell

[911hillclimber]

The AOS function is to separate the fine oil droplets suspended in the ever moving (panting?) air in the engine.
As the engine prays oil everywhere some gets in the internal air of the crank case as a mist. The AOS gets air drawn to it via the inlet depression and it comes up into the AOS plastic body, settles in the square chamber and the oil drips down to the sump but some air is passed to the diaphragm valve which deliberately passes into the tube I refer to as wet with neat clean oil. The separator I think is not a fine filter, it only removes some of the oil in the crankcase air drawn into it, some fine mist goes into that tube to the inlet and the mist is burnt off during the combustion of the engine.

If the oil content is high however then you will get a lot of oil in that tube and hence white smoke.

I am not at all sure my problem is a duff AOS after today's work.

Ages ago I held the thought that one or more of the piston rings in this engine have migrated to the '6 o'clock' position and the hot thin oil seeps past the ring through the gap and to the combustion chamber. However, all 3 rings gaps need to be approx. in this lower position for oil to flow from under the piston to the comb chamber, all a tall order, but I do feel rings rotate around piston grooves in an engine unless the engine is a simple 2 stroke design where the rings are pinned to stop them rotting around the piston.

If the sump is very full of oil then when the engine is stopped some oil will puddle in the bottom of every bore, maybe some more than others and this hot oil will rest against the lower ring.
If this oil can get past then you have oil ready to burn white (smoke).

 

[Motorhead]

Graham,

I wouldn't be too despondent. You say that "the suction pull on the oil filler cap is much reduced and the engine stumbles far far more noticeably when you free the cap from the neck", so clearly the new AOS has had a positive effect despite the one you removed appearing to be fully functional. My only thought is that if you were able to get your hands on a suitable manometer, perhaps you could confirm that the crankcase depression is within spec, whatever that might be?

Fingers crossed you've found a cure (finally!!), but reducing the oil level could provide a last-gasp solution if not. As you say, you'd have to be very unlucky for all 3 piston ring gaps to be aligned at BDC on one or more cylinders, but in the world of statistics nothing is improbable or impossible, and excessive oil in the exhaust is never desirable for cat converter durability.

Jeff

 

[911hillclimber]

I've searched in vein to find a drg of the Boxster MA1 engine that shows the bores in relation to a full sump.
Is the sump oil level just below the bores, or well below?
If the latter then dropping the oil level a notch will do nothing.
I let the car idle for about 10 to 20 seconds after a run before switching off.
This allows most of the oil in the engine to drain down to the sump so the level will be at it's deepest, but still there will be oil squirting all over the place during that time.
Inevitably, oil will puddle in one or all of the bores, so oil will always be resting next to the rings, but this is the case on all boxer design engines, Porsche, VW, Alfasud and Subaru.(and others)

I have 3 Porsche flat 6's and only this one smokes. My 360 bhp Subaru Impreza never smoked...It is just this one engine!

Planning some runs over the next 2 weeks, so time will tell.
Thank you to everyone who has chipped-in with ideas and support. []
Graham.

 

[911hillclimber]

Couldn't resist a day out in mid Wales, so a cold (smokeless) start and to Bishop's Castle and on to see the Red Kites being fed and back, 197 miles.
Car ran an absolute dream, even 34.8 mpg but every engine start was smoke-free.

One Swallow does not make a Summer, so we shall see as things progress. I might yet fall in love again, but the wife mentioned a 997!

 

[legin]

Slight tangent. What wheels are those ?

 

[911hillclimber]

They are Italian aftermarket, squeeze formed, but can't recall the make, sorry.

I first thought they were optional wheels and I searched for ages to identify them, they are similar to Spyder wheels I think.
They came with the car. Wider than stock, 19" and seem to weigh a lot when getting them off and back on the car.
They do fill the arches well!
Haven't seen them on another Porsche in last 3 years.

 

[legin]

They look good and they very similar to 996/997 GT3 wheels, 997 given they are 19"

 

[911hillclimber]

Yes, you are right, and I thought they were GT3 wheels and wondered why this basic car had them, but there are differences.

Best bit about them is they are very easy and quick to clean!