This is a genuine BMW chain tensioner, part number 11 41 7 505 842. The number stamped on the part is 11417505842; BMW's catalog files it under the short number 7505842. You will find it on our Engine shelf, under Oil pump with strainer and drive.
It fits every E46 body style (316i, 316ti, 318i and 318ti, 2001–2004), with the N40, N42, N45 or N46 engines.
BMW draws it on the Oil pump and compensating shaft drive (11_3175) diagram. It weighs about 80 g (0.2 lb).
We have not had one on the shelf yet. Request it and we will tell you when one comes off a car.