The part i took off was a large flat plug, behind this was a spring and a metel bit. Should there have been a ball bearing as well (im assuming its some sort of non return valve?) there was no ball bearing, the metal bit was flat on one end and had a depression in the other.
That is the pressure relief valve. Be very carefull when putting the plunger and spring back in must be spotless and able to seal the oilway but still able to move. I realy think you should get the sump plug out even if you have to cut a slot in it and use an impact driver.
Ok thanks for the help. Have just dumped all the oil again, and will check the valve. Fixed the oil light, coolant gauge and fitted a new fuel filter plus cleaned the carb out today so ready for our first camping expedition!!
Still waiting for manual, amazon slowest delivery ever! been waiting a week!
If this is the correct assembly of the oil pressure valve, as below. I think it is but id like to be sure (wouldnt want to break the engine on our trek!)