Astra 17dti can not fit cam belt not timing up as i have changed head gasket?

What year is your astra? Do you know if the isuzu engine is fitted or vauxhalls own engine? If its the vauxhall engine then you need to time the cam up with a specail tool and a dti guage.Astra 17dti can not fit cam belt not timing up as i have changed head gasket?align the timing marks on the crank shaft and cam shaft the pump should have been locked up before strip down,fit belt adjust tensioner remove lock pin turn over by hand make sure all marks line up and thats it.