I think if the oil pump was the problem Sizewell GM would of just changed it. The problem seems to be the oil & how easy it can get contaminated even there own creation Dexos hasn't helped stop it happening. GM have tryed several chains over the years but they still seem to stretch. These V6 engines were all well tested & in the US & OZ, it was also developed by an international team of engineers including input from Ricardo PLC, there's lots of them in different versions from 2.8 upwards. Some are made in Japan, Mexico, Canada, OZ & the USA. (Our 3.2 was made in OZ) over it's production run which is still current & no doubt all sharing the same oil pump too. They make something like a 1,000 engines a day so why this chain still fails without neglect is beyond them.
What history I have; with the old twin-cam Berlina's, etc, etc, when wear occurred on the chains, it generally seemed to be even across the sprocket i.e., top and bottom. The pictures shown earlier; with so much apparent chain stretch, seemed almost as if there was an extra link. Also, wear seen was on both sides of the "Trough"; mid point, of the tooth, implying, the pin was not fully sitting in the "Trough". It was also said there was little wear on the tensioners, despite the apparent stretch. For me, the only explanation is, the chain and sprocket do not match. Vis a Vis, there is some variation in the length of the links. That would result in the tensioning load sitting on the "slopes of the tooth and not fully in the channel of the tooth. Is there any chance, that a variation, minuscule; and it need only be minuscule, in chain link length/sprocket - lost for the right term at the moment - tooth contour - for want of a better word, could result from different manufacturers of these items; different machining tolerances? Those pictures imply to me, the chain and the sprocket are not matched. The chain is rotating in one direction and therefore, simplistically, predominantly wear should be on the driven face, and not on both. I could be barking up the wrong tree, but I would, even though it seems extreme, go as far as not to trust just replacing the chain, but also the sprocket, from the same supplier. I know that is an extra expense, but it is not unusual in industry; the Aerospace industry for instance, to have matched components.
Is it also possible, we essentially have two problems: Chain/Sprocket match and Oil starvation.
On the former, I will check with the guys who did my engine where the various components came from.
With regard to the latter, the observation about switching off the engine when sat in traffic jams is pertinent, given Alfa state, the oil pressure, derived from the crank mounted oil pump, varies with RPM from 3 to 6 Bar. This is on a new engine.
In high pressure Oil and gas systems, to minimize risk to personnel, with regard to instrumentation, "Snubbers" are used, to reduce the pressure by "X" times - one does not want a 200 Bar line bursting in an instrument when someone is calibrating it. All oil, water and gas lines have an effective pressure reduction, even without the element of clogging due to sludge is taken into account. There is a formula somewhere. And the length of the line/gallery adds to the pressure attenuation. Plus wear on journals and bearings, ultimately reduce this pressure further.
Knowing this, I was just pondering whether a supplementary oil pump, operating in tandem would help sustain the "Tick - over", "Low RPM Driving".Pressure. It always makes me laugh when supposed experts and celebrity car programs quote "The engine is so torque-y, one can accelerate from 30 mph to 140 mph is top gear! Think of those poor journals, grinding together because, mechanical pumps aren't very good at low RPM. That's why manufacturers give us a gear box. And some people can get a quarter of a million miles out of an engine and others; hypothetically speaking five thousand.
Anyway, I'm a retired engineer, I'm bored, I need a project and my Q4 seems like a good one. It can be done, I'm sure of that. It's just a question of how best to achieve it. I need first of all to take some pressure measurements at key points in the system. The more I read about this engine, the more I respect it.