I'm finding people don't have much knowledge of the multi-stage pumps so I thought I would share everything I could.
There have been a couple manufactures of the the multi-stage pump and to my knowledge all the parts interchange with each other.
Hamilton made them for a while, now Kodiak (KEM)is making them, and Marine power.
Lets start at the grate. Most come with a 13 bar grate but a 9 bar is available. Our experience with the 9 bar grate is better performance but it also lets bigger sticks enter the pump so I would not recommend the 9 bar in areas with lots of trash. There also is a stomp grate available though I don't have any experiance with it.
Now off to the impellers. Hamilton and KEM both have impellers very simular to each other. Both have what is called the overlap with is a 4 blade impeller that looks like this
Also what is common with the lead impeller is a standard impeller with a bullet shaped piece of brass infront of it. The overlap does cut down your RPM's a little and is suppose to load the pump better but I get mixed reveiws with it. But recently Scott started producing a new lead impeller which they are calling their bullet impeller. Same idea but this impellers blades are longer, there is 3 blades instead of 4, and it feeds the pump and keeps it loaded. Its showed in the fallowing picture.
Okay now lets look at what fallows. The housing is called the stator. The fallowing picture shows the stator in place. With the first impeller still in the boat. My understanding is the fins inside the pump help stop the rotation of the water as it goes threw the pump. When these get holes or start having fins break they need to be replaced.
Okay now the wear ring is inside of this and is the surface in which the impeller is running inside of. Now take your impeller and push it to one side and measure a gap between the impeller and the wear ring, if the gap is greater then .075" either your impeller or wear ring is wore out. The fallowing picture shows the impeller in place so that it can be measured. Remember push it to one side so that the impeller touches then measure the opposite side.
Okay now to measure the impeller you mearsure the diameter. Measure from tip of blade across the impeller to the opposite side to the tip of the blade if the measurement is 7-5/16" or less your impeller is wore.
Okay now common problems that can cause the pump to perform poorly.
1. Something is in the pump. (You laugh but they will run with a stick stuck between stages)
2. Pump is wore out.
3. Impellers are damaged.(Nicks and dings)
4. Impeller put in backwards. (Very easy to do and yes it will usually still run)(Looking at the pump from the rear the impeller should turn Counter-clockwise.)
5. Impellers in the wrong Order. Remember less pitch then more pitch as it moves towards the back.
6. Impellers are the wrong size. (Over reving or lugging the engine) (Boat blows the pump out)
7. Multi-stage pumps have a bucket adjustment make sure the bucket is clearing the jet stream.
8. Poor reverse! Make sure the bucket is dropping far enough. Again they have an adjustment.
9. Hard getting in reverse. (Idle is to high)(Bad cable)(Cable is in a bind)
These I have found to be common problems that people run into sure there are more but I see these alot.
Okay now you ask how to tell the impeller pitch. On the rear of the impeller you should find one of the fallowing 3; numbers that say the degree of the impeller, a number that is the part number, or letters and numbers. Here are the ones I have ran into.
#5 19 degree
#4 24 degree
#3 23 degree
#2 22 degree
80620 Course Impeller for 771
80609 Standard Impeller for 771
JE104 Fine Impeller for 771
JH106 Standard (19 degree) for 772-773
103348 Course (22-24 degree) for 772-773
If for some reason there is no numbers there is one other way you can tell what you have. As close to the base of the blade as you can get (Part that attaches to the hub) meassure the distance between the back of the blade to the front of the other directly above it. Take that measurement and multiply it by 12 and you have your pitch. For example the distance on a 24 degree impeller will measure 2" from base of blade to front of the other. I measured another 1.58" with a micrometer multiply that by 12 and you get 19. That would be what Hamilton said the pitch should be. I checked this with 5 impellers and they all came out correct.
Please feel free to add more info or correct me if I'm wrong. Also I have tons more info so if you have anymore questions please feel free to contact me.