Jimo's instructions are essentially correct. I did the t-belt change on my S90 a while back. The water pump had been replaced on the previous belt change so I left it. It is a very wise move to get a new tensioner and idler, (and a new WP if you don't know the history)...not just a new belt! I got the full Gen. Volvo kit from FCPGroton, I don't know if they still offer it. Price was decent....5 years ago.

When you have the 2 camshaft marks aligned as Jimo indicates, you can safely assume that the crankshaft is positioned correctly...really it has to be or the engine would not have been running ok. I didn't even try to find my crank marks. There is no need to remove the harmonic balancer or anything on the front of the crank - just the little metal t-belt shroud as mentioned.

Re-check the cams' timing marks when you're done and you will be OK. As this is your first go at this, take your time and think carefully about each step. Next t-belt change will be less then half the time.

Of course I was holding my breath as I fired the engine, but all was well. I sold the car 20k miles later, but see it around town now and then, so I can call my DIY T-belt job a success.
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Bob: Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), 98 S90 (recently sold) and 2010 XC60. Also '77 MGB and four old motorcycles