no oil to rh rockers

just did a rering job on a 318 that I got from a wrecking yard it didnt have too many miles on a previous rebuld, so I just put new rod and main bearings in and new rings. put the engine together and installed it in the car. Spun the oil pump to check the pressure. the pressure is great and plenty of oil comming thru left bank rockers but could not get any oil to the right bank. removed rockers and still no oil. ive never had this happen before. can anyone tell me why I have no oil to the r-hand head, before I pull the engine out.