Mike Rocket
Rocket 3
It is possible to fit the non return valve in upside down when you are refitting the bottom sump plate. I do not know if it would stop the oil flow to the pump though.when working on something that someone else has work on u need to consider the fact that u have the original problem plus the problems he created while working on it. (maybe several things wrong.)
u might start by pulling the three oil drain plugs. this should drain the storage tank. check for debris in the oil. cut around the filter near base then open it up to see what is in it (if u cut it with hacksaw it will have the material the comes with sawing. )
the more info u can give us the more info we can give u.
wjb post looks like a good starting place.
there is an anti drain valve that may be in backwards?
i guess my opinion would be go in the front and check out what wjb said and see if thee chain is turning the pump ect.