Thanks for the very informative message. I have heard that about the long service intervals in a few places, but is the problem not accelerated by the sprockets being too sharp which guide the chain?

I asked Honest John and it was said that the timing chain is still at the back of the engine and he has not heard of any failures after 2011.

Even with the new 2011 design and a service (inc oil change) every 10k miles, will I still need to eventually replace the timing chain after 100k miles or so?

If so, is this still going to be a £2000 - £8000 job as it's still an "engine out" job?

Thanks

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.

Absolutely spot on but im yet to see the N47D20A engine fail in a car that doesnt have suspect service history, this in my opinion being the true cause of so many failures. Lease companies hire cars out on maintaince free contracts of normally 3 years 36k miles, you get the car serviced every year and hand it back at the end of the period with the mileage at no more than 36k or you pay a fee for every mile you go over. Unscrupous individuals or companies do as many miles as they like and just clock the vehicle prior to the hand back with a fully stamped service book. Invariably joe punter buys what he thinks is a low mileage car with provenance but in reality its far from it. Why do you think so many companies are still offering mileage adjustment, it can only be of use for cars of under 3 year old as all mot mileage is now recorded.