oil filter blows off

i have a74 mgb, the motor was rebuilt an when i start the car the oil filter gasket blows out an all the oil comes out can some one tell me why????

What filter are you using, manufacturer name and filter number? Who rebuilt the engine, were some brass plug removed from the block and replaced by the engine builder? Have you noted what the oil pressure gauge does when the engine starts? Assumung the oil filter is installed correctly the most likely cause is the engine builder installed a plug in the oil pressure relief hole on the bottom of the block. The oil pan will have to be removed to check. On the bottom left rear of the block there are three holes in a line. The two smaller holes should be plugged, the center hole is bigger and is the oil pressure relief oil return passage, it should not have a plug. If its plugged oil pressure will be excessive and the weakest link (oil filter) in the oil flow system will burst or blow off.

Clifton

What filter are you using, manufacturer name and filter number? Who rebuilt the engine, were some brass plug removed from the block and replaced by the engine builder? Have you noted what the oil pressure gauge does when the engine starts? Assumung the oil filter is installed correctly the most likely cause is the engine builder installed a plug in the oil pressure relief hole on the bottom of the block. The oil pan will have to be removed to check. On the bottom left rear of the block there are three holes in a line. The two smaller holes should be plugged, the center hole is bigger and is the oil pressure relief oil return passage, it should not have a plug. If its plugged oil pressure will be excessive and the weakest link (oil filter) in the oil flow system will burst or blow off.

Clifton
Or, someone possibly buggered up the releaf valve.