Rover 214 Crankshaft oil seal keeps popping out

Sounds like the crankcase may be getting pressurised - check that all the breather hoses are clear. Another possibility is that the head and/or bearing cap ladder have warped, causing the hole for the oil seal to open up - this would be obvious, as there will be a gap at the mating surface. Only other thing would be camshaft bearing wear, the movement of the camshaft working the oil seal out.

It's been turning in the housing and is no longer a tight fit. Clean thoroughly and install with Loctite bearing seal - and allow time for it to set.

Assuming that the new seal does not just fall into the hole (ie it is a tight fit) Then the engine breather system is probably blocked.

The easiest way to test is to fit a new seal then start the engine, slowly undo the oil filler cap, if there is significant pressure (which will be obvious) then check the breather system. Other than that a severe crankcase pressure overload caused by a worn out set of rings (or related, like headgasket blown between cylinder and oildrain) can cause it, but if it runs ok then that is not likely.

MrCheerful