I hope this helps someone, I have had the oil pump apart before and knew it was a bastard of a job and quite confusing at times. My engine casing got damaged so I had to get it welded and thus remove the oil pump before handing it over to the shop. Before removing the oil pump you should make a couple of alignment marks on the barrel relative to the engine casing. This is not a fall proof method for reassembly as I found out but it will confirm when the barrel pin has lined up with the hole in the engine casing. On reassembly despite my previous experience I still struggled with the nuances of reassembly. For instance, a problem that had me scratching my head this time around was the plate and oil pump cover not lining up with the locating pins in the engine casing when they were on the pump driveshaft. I figured this out when I realised that the pump barrel is lopsided and if the locating pin in the barrel isn't in the hole in the engine cover, the driveshaft won't be central and that will put the backing plate and pump cover off centre and thus it won't line up with the locating pins in the engine cover. You can tell when the oil pump barrel is correctly located in the hole in the engine casing because the backing plate and pump cover will line up with the locating pins in the engine casing. Also the barrel will be level with the surface of the engine casing (where the cover screws on), if the pin isn't in it will be about half a centimetre above. Here is the hole in the engine cover pump housing I am referring to: Here are the components that I mention: When the barrel pin is correctly in the hole in the pump housing on the engine casing it should fit together like this: I think the locating pin may come out of the barrel and could be put in the pump housing on the engine casing but I don't think that would make it any easier. The tolerances of the barrel inside the pump housing are such that it is difficult to accurately rotate the barrel when it is in the housing to line the barrel up with the pin. This means that normally you have to take it all out again if you don't get it right the first time. I found the best method is to assemble the back rotors, barrel, washer and driveshaft all in one so that the washer keeps the back rotors from falling out as you put it in. It also helps to hold the engine casing upside down. Another problem you might come up against is the pump not turning when you put the cover back on. This is due to the gasket compressing too much and the pump cover pressing down on the end of the pump drive shaft. Don't panic, it just means you need a new gasket. I hope this helps someone with this fiddly and exasperating job! Another tip, if you find your gasket/backing plate and oil pump cover being miss aligned like this: It is due to the backing plate being upside down. Turning it around 180 degrees solved it. Lastly, do not underestimate how sneaky the oil pump housing is. It will try to trick you into thinking you have the pin in the slot when you really don't. Sneaky oil pump housing! Observe: There was nothing to tell me that the barrel wasn't aligned from this. The oil holes in the barrel were in line with the oil holes in the housing. The only clue was that the barrel was only slighty proud of the oil pump cover. To get the barrel in is a tricky business and you will find yourself having to hold the clutch cover casing in all sorts of different ways to be able to line it up and get it in first go. PS: This is the wrong way around for the oil filter: The o ring goes in facing the housing! It will still pump but a lot will leak out of your housing.
