My 91 318i kind of sounds like a diesel when running

[bmwm42]

i would suggest the same replacing the tensioner on already worn parts is flat out retarded, you are going to wear the guides at a faster rate. do your self a favor and replace them all at once.

[genocide98]

Desktop Dave from M42 club advocates caution when replacing a tensioner in an unknown condition timing gear setup. I would suggest that you start saving for an entire timing gear/chain overhaul, if you want to keep the car that is. Also, be sure to read up on installing the piston, I cannot remember if it is to be installed compressed or extended, and what the break in procedure is exactly.

You install it compressed, then you press the guide against it to release it, it'll take a while for the pressure to build, so you might want to rev it for a few (30?) seconds on startup.