Changing your water pump will not throw off your timing.
Im not sure about the 98s but there is a service bulletin out there recommending replacing your plastic impeller pump (if you are equipped with it) because there has been incidents where the impeller litterly falls apart on you.
I had the stock plastic impeller on my dealer maintained car with 80k. I replaced it when I did my pulley kit, fan delete, thermostat, and anti-freeze swap in the fall. If I wasn't changing anti-freeze I probably would of waited.
There was no signs that the impeller was on the way out. I did see a picture on a forum of an impeller that was cracking when it swapped out at the same mileage.......
1996- BMW 328IS
<img src='http://img.photobucket.com/albums/v242/gws226/TEX/neverleanedsig.jpg' border='0' alt='user posted image' />
Performance: Zimmerman Cross Drilled Rotors-- PBR Deluxes-- Cosmos CAI---- Turner Pulley Kit--- Fan Delete mod---
Beauty: 18 polished M-Parallel replicas, Inpro Euros w/ Enchanced Angel eye kit, 20% tint
Clear corners/sidemarkers ---- Eurospec (Depos)
To do list:
UUC System U TDM- 3/05
M50 manifold converstion 3/05
off to the tuning shop for custom software 4/05
Cams/lightened flywheel, throttlebody........ well lets see what happens