Please don’t continue to run the engine relying on petroil because the main bearings and sealing glands are not getting any oil and you will soon do some damage. From your description of its behaviour I would also suspect stuck or broken piston rings, closely followed by missing cylinder base rings and/or wrongly fitted glands. You do not need to remove the cylinder head from the barrel to sort out your problems. I recently came across a Scott where the rebuilder had wrongly connected up the pipes to the oil pump! Do check that the supply pipe to the pump goes to the correct orifice on the pump body. This is usually the one at front/right, but there are some oddball pumps around with different internal drillings, and the feed connection elsewhere. Another thing to check is that the union that screws into the oilfeed hole on the pump is not too long and obstructing the internal drillway. I have recently rebuilt a batch of pumps and found all sorts of other rebuilder’s cock-ups such as plungers swapped into the wrong side, blobs of gasket goo blocking drillings, etc.. To check that you have the correct rotation of pump, you look at the drive end, and there should be an anticlockwise arrow engraved or stamped on the body. Pumps on the left-hand side of a Scott, such as 1939 Clubman Specials and some Sprint Specials, are opposite handed and not interchangeable. Internal parts are also not interchangeable.
Hope this helps.
