Harmonic Balancer B200 & B230 engine
Volvo began using a crankshaft vibration damper in 1985 when the B200 and B230 engine series was introduced. The damper helps to reduce the vibration inherent in all 4 cylinder engines. A small section of rubber separates the inner and outer portions of the crankshaft pulley. Over time, the rubber begins to weaken and allows the outer section to rotate around the inner piece. This can lead to squeaky noises coming from the engine bay that sound like loose belts. The ignition timing marks will no longer line up and when using a timing light you will see the timing marks slowly rotating as the outer pulley slips.
Some owners have reported cases of the outer pulley moving inboard enough to allow the belts to rub on the timing belt cover. If yours is exhibiting any of these problems, you should replace it before it fails and leaves you stranded.