The timing belt should be replaced every 50,000 miles. The B230 engine is a non-interference engine, meaning if the timing belt breaks, the valves will not impact the pistons, causing great damage, headaches, and loss of money and/or time. But, if the timing belt breaks, it will leave you stranded.
Symptom: hit ignition "Start"
while someone removes the oil filler cap to see if the camshaft
rotates. If the camshaft does not rotate, then most likely it
is a broken timing belt.
On the B230 series (240 late models/740/940 Volvo) engines, the crankshaft pulley is held in place by the crankshaft bolt (unlike the 6 fasteners on the non-B230 engines of the 240 Volvo). This crankshaft bolt is difficult to loosen and remove unless you have the special crank pulley holder tool shown above. (Some die-hards prefer to remove the starter motor and have an assistant jam a heavy screwdriver into the flywheel teeth to stop the crankshaft pulley from moving while loosening the crankshaft pulley bolt. But this requires another person to help, adds extra work, and may damage the flywheel teeth.) Having the Volvo 5284 crank pulley holder tool above makes changing the timing belt a lot easier and is easily worth the $48 cost (IPD). Moreover, while it isn't exactly necessary to remove the crankshaft pulley bolt with a torque wrench (you still need a long handled wrench and a lot of muscle power), you do need a torque wrench to properly set the tension on the crankshaft pulley bolt on installation.
Check that the tensioner roller spins freely. Usually, it should be replaced every other time the timing belt is changed. Check to see that there are no oil leaks around any pulleys. If there aren't any leaks, then you may choose to not replace any oil seals. But I recommend changing the oil seals every other time the timing belt is changed. Some people replace everything as a matter of course. It's up to you.
Caveats: I've read of other people who have used (a) an impact wrench or (b) a long handled wrench set hard against an obstruction, then hitting ignition "Start" to turn the crankshaft to loosen the bolt. Realize that the crankshaft pulley boss (the gear) is not as hardy as the old one on non-B230 engines, and its locking knob (for the crankshaft pulley/vibration dampener) may break off. Also, one DIY'er used an impact wrench to set the torque on the camshaft bolt and broke it off.
Also, Volvo changed the tooth profile of the timing belt, I believe, in the early 1990s, so check your old belt and make sure your new belt has the same profile.
Download now by clicking on link below:
A Step-by-Step Guide to Changing the Timing Belt
on the 240/740/940 Volvo, B230 Engine
Appendix A: Replacing tensioner roller, with instructions for making a jig to pin the tensioner spring
Appendix B: Replacing overhead camshaft seal, intermediate shaft seal, and crankshaft seal