I'll give my verdict on these BMW timing chains, but first ...
...my background (to hopefully show that what I'm saying has something to back it up) : I used to work for a major oil and fuels company, in oil development and testing (on the Wirral) My current job is more in the oil extraction side of things, still testing, but a very different field.
There is, and never was, anything inherently 'wrong' with BMWs and timing chains. The problems have occurred due to two primary factors.
1. The long 'official' BMW service intervals. These were brought in to keep the fleet market happy, who get rid of cars at 3-4 yrs old and 60k miles. If only 2 or 3 oil changes in that time, then maintenance costs are greatly reduced. However, oil that has done 15-18k miles has suffered a horrible amount of degradation, and its lubricating properties are pretty much shot. Fast forward 4 or 5 years, and those timing chains end up getting stretched, jump a link, and the engine is goosed.
2. People not cooling the turbo (especially on diesels). After a long run at speed (motorway, for example), you pull into the service station and switch off the engine immediately. The oil that is around the bearings of the turbocharger stops moving, and sits there. The turbo is at a high temperature, and that oil basically gets cooked. Some of it turns to solid carbon. Eventually, those lumps of carbon dislodge and move around the engine. You HOPE that they end up in the sump. However, they'll also tend to get stuck in any really small pipe/mozzle - like the ones that spray the oil onto the timing chain to keep it lubricated, for example. Those block up, no oil on timing chain, engine goosed again.
Basically, to greatly avoid these problems : change oil/filter at most every 10,000 miles, and idle the engine for a minute or 2 after a long run at speed, or if you've been towing.
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