Hi and welcome to mightyram. The oil pump sprocket should have full free movement when the belt is off so something is up. I would not attempt to install any belts and set timing etc until the oil pump housing and attached balance shaft has been pulled and inspected. If the balance shaft bearings are shot, it'll chew up the pump and result in a catastrophic loss of oil pressure. When the balance shaft bearings fail they automatically cause a severe loss of oil pressure - it'll take out #1 main journal and rod bearings, seize the engine and rip up the cam journals in the head. Check the engine oil for metal and it's general condition - it will give you a clue on the status of the engine. We have a downloadable PDF for setting the timing on the G63B engine (they are actually pretty easy to work on) - http://www.mightyram50.net/vbulletin...2&d=1371362714