old mercury 4.5hp ..havin trouble with water pump

i have a 1979 mercury 4.5hp motor w/ serial # 5271459
upon takin the foot off and checking the water pump and checking the impeller inside i found out that the impeller was eatin to pieces.. i went out and bought a new impeller and replaced it right and still no water pumps out... i took the foot of again .. a total of 6 times and checked to make sure the impeller was turning the right way but no water comes out up top ... just hot exaust.. is there a oring that goes in there on top of the impeller that keeps air from suckin inside the water pump base and top? cause i saw a pic of a impeller kit and it had both impeller and oring and impeller plate .. my plate was good so i didn't replace it.. should i have? cause no oring was in there when i took it apart.. would a oring being missing cause it not to pump water up into the engine and out the spout?..........somebody please help me with this problem

Re: old mercury 4.5hp ..havin trouble with water pump

I just had to replace my first impeller that had literally disintegrated, on a Merc 3.3. Have you verified that all paths are clear? I found a lot of tiny pieces in the very bottom of the foot where the water intake holes are. It took a lot of shaking upside down to get all those pieces to fall out through the small pump intake holes ? I also used my earmuffs to flush the foot, holding it upside down, to help get those pieces out. Have you blown through the water tube to make sure there is a clear passage from the pump up to the motor and out the discharge tube? I had a small piece clogging the rubber tube - luckily easy to clear.
As far as whether you need a washer or not ? I?d recommend trying http://www.crowleymarine.com/ - It?s a really nice site I found that has complete schematics for motors, including OEM part numbers, and is very easy to order from - each part indicates how long it will take to ship, down to washers and o-rings. Just click on 'parts catalog', then pick your make (pick a different make, then your make, otherwise it won't populate the 'year' pull down list). Once you find your model you can go right to the schematic/order form. It should at least help you figure out if you're missing a part. I ordered from them and they came quick. From what I found in the marine parts types of webs, it?s very good, you can even go in and check the status of your orders, they email when you order & when they ship etc. FYI - If in doubt and it's $1 or $2 - order it anyway. It'll be included in your shipping and may prevent a week or more delay if you have to order something else (I had to) or save you visits to 4 stores on a Saturday night to try to find that $1.25 o-ring you could have ordered with the rest (also happened to me).
I wonder if there's a way you could jury rig a drill to turn the shaft while the foot is in a bucket of water - to let you see if water shoots out the pump or not? May help nail it down to the pump, or a supply tube clog?

Good luck,
Mike