Let’s start:
The 305 engines can use anything they can get in the way of oil pressure. Stock pressure is low to begin with at (1 - 3 psi at the most) but only degrades over time with bad gears and housings. A careful look at the oil pump gears and housing needs to be made to ensure your new rebuild or restoration will last for miles to come. Here are a couple of photos that show what you might need to look for in your oil pump.
This first picture shows the housing and the groves that have been gouged into the metal by foreign material that got sucked into the pump. Look at the top gear cavity in this picture especially. You can see the groves there. These groves degrade the pressure of your pump and this in turn starves your engine of oil in some of the most critical areas.
DSCN0059 by adam.corts, on Flickr
This next picture shows a set of gears out of this same pump. Look towards the tips of the gears or the end of the teeth. See the groves in the end here. This also degrades the pressure of your oil pump. The oil is allowed to escape through these gouges and decrease oil pressure to the engine.
DSCN0063 by adam.corts, on Flickr
Unfortunately I believe these parts are trashed. Could they work . . . yes but I decided to get new or better gears and a new housing. Didn't want to take any chances. Comments welcome. Maybe there is a way to save these parts?
Let’s look at possibly improving the pressure of this oil pump. The gears sit in the housing and are covered by a thin paper gasket and then the cover. If you could get the cover closer to the gears this would increase the pressure of the pump. One thing I think you can do is to take the same amount of material off the housing as the thickness of the paper gasket. This is a very small amount and should be approached with caution. Too much and you’re in big trouble, the gears will drag on the cover. What I did was measure the housing in a few spots, then measured the thickness of the paper gasket. This paper gasket measurement is the absolute maximum you should take off the housing. Be careful, I set up a piece of glass and a piece of 400 grit sand paper (to keep the surface flat) and started lightly rubbing the housing surface until I took the right amount off.
DSCN0056 by adam.corts, on Flickr
After the right amount of metal was removed from the surface I cleaned both the housing and the cover. Make sure there is no residual paper gasket material left on the surfaces. The housing should be good to go after the light sanding but the cover could use a touch of sanding too. Very little here just enough to clean the paper off. Use other methods to get the old paper off if you like. Then, once clean I started the assembly.
DSCN0064 by adam.corts, on Flickr
This picture should show how the parts go together the only thing not shown I believe is the second washer (Not shown or listed in the parts diagram) which goes on the main drive gear shaft (the gear that is driven by the crank gear) before it goes through the housing. I have two pumps that came with these two washers, so if I'm wrong here let me know. I was surprised to not see them in the parts diagram. Only one was shown and listed. I lightly oiled the gears and the shafts as they went together. I was careful to keep the mating surfaces clean and free of oil so the paper gasket could do its job.
Once together the rest should be easy. I installed the pan head screws and tested the gear movement in the correct direction of movement. Seems to work great.
DSCN0069 by adam.corts, on Flickr
Please add comments and concerns. It is my hope that by the end of the post with your help we can have a complete rebuild tutorial of the 305 oil pump. If you don't like the upgrade to the pump please share your ideas and concerns. I hope this helps.