Piston slap in Volvo motors is annoying but nothing to worry about. The 245 beater I bought 6 years ago with 123k sounded like a diesel on start up, then would quiet down fully warm. It has 241k now and sounds exactly the same. Here is a simple test for oil pressure without a gauge, provided your light works--engine completely cold--start it--does the light go out right away--shut the motor off--turn the key back to ignition on--watch the light--does it take a few seconds for it to come on due to residule pressure in the sytem? if yes, you have good enough pressure and the likelyhood of a bad crankshaft bearing is remote.