[supernova1]

I have 2013 (January build) X3, 60K that started producing high pitch whine at 2-3k rpm. I turn off ASS each time I start engine. I also do not usually rev up the engine, although I have no idea about previous owner driving style.

Dealer was great to offer the whole set (timing chain and oil pump chain) replacement under CPO warranty.

To my surprise they did not replace original chain tensioner (11317567680) with updated part 11318685091.

I know that updated part has the same size but has much stronger spring. I try convincing myself if timing chain really needs that much force or it just leads to its premature stretch and plastic rail guide wear. Anyone can comment on this?

As for oil pump chain failure, I tried looking everywhere for possible cause. After very long search, it seems to me that chain metal is too soft for this application - either design or manufacturing flaw.

I used these picture as a reference: https://fotki.yandex.ru/next/users/a.../597166?page=0

Oil chain is of silent type. It consists of 4 thin plates per link (one link has 2 plates per 1 tooth and 2 outer plates, and another one has 2 plates per 2 teeth). What happens is that chain sprocket flattens all teeth making them a bit thicker. This leads to chain losing its flexibility, and that friction of distorted plates of adjacent links against each other creates force that leads to each tooth plate pin hole elongation, and eventual chain break. Pictures of broken chains usually show that inner 2 plates break at the pin hole wall, despite presence of outer 2 guide plates that are supposed to share tension. Chain pins are fine - measurements showed no size/shape change.

If you look at the updated oil chain pictures, it has 2 thick solid plates that replaced 4 thin plates of link with 2 teeth. This allowed designers to slightly taper that link 2 teeth thickness, eliminating effect of teeth getting thicker - adjacent link teeth no longer rub against each other even if they are distorted with time.

I believe that old chain design/manufacturing is flawed, and they will eventually break regardless of oil quality and oil change intervals. The only way to prevent this is to replace old chain with new assembly (11417605366)