Water Pump Kit Installation

This article does warrant some pictures so bare with me as I go through this process.  What sometimes is supposed to be realllllllllllllllllllllllllll simple to do, can turn into an outright nightmare.  Good thing I'm cheap and stick it out so I don't get hosed by some unscrupulous mechanic!


I only had 425 hours on the Yammy F150 when I decided to complete this project.  If you read about water pumps and their impellers, the manufacturers recommend every 2-3 years.  I suppose if you put on 300 or so hours on a year and in dirty water then that prediction could be right.  However, after taking my unit apart and looking at it, I could have gone another 425 hours on it with no problems.

Wherever you decide to work on your motor, if on or off of your boat, make sure its in a spot that it can be moved if necessary.  I thought this would be a 3-4 hour job but it turned into more like 10-12 hours, due to unforeseen circumstances.  Obviously because of the size of my motor it was left on the boat, backed into my garage for easy access to tools and stuff.  I first took the prop off and found my first malfunction.  Although I dinged the prop just recently at the boat launch I hadn't taken the prop off to fix it.  What I found was that the brass spacer that sits behind the prop and actually holds the prop away from the aluminum casing, was 75% gone!!!  I mean, it was busted and all the pieces somehow vented out through the small spaces where the exhaust exits the prop.  I found a replacement spacer at a local dealer and the mechanic there said that in 33 years of marine stuff never saw that happen before.  What could have happened would have been catastrophic to say the least.  I'm guessing that if the rest of the spacer had broken off that the prop would have gone into a death wobble and imploded the gearcase of the outboard!

As long as I was working on the leg I also figured I may as well change the leg oil, a maintenance thing I do every two years anyways.  There are the two screws that need to be removed and drain the oil out, replacing it with a quality Marine grade gear oil.  I use Shell Nautalis in my legs.


I should point out that I do have a very through manual on my motor and while it did help alot during this procedure, it would have helped alot more if I had read it properly!  My leg has two "split" areas, both held by 6 bolts.  The book did not say whether it was the top or bottom "split" that had to be removed but from all the pictures in the manual I was able to make a good guess and got it right.  What I failed to read was something about a "hidden" bolt that needed to be removed.  I assumed it was this (photo) bolt that was hidden beneath a small rubber grommet.  However, it turned out to be this (photo) beggar that was located under the trim tab!  I failed to find this bolt and after much swearing and beating with a mallet and being almost brought to tears, I re-read the book and looked at the pictures and finally figured out what was wrong!  When I took this last bolt out the entire leg fell apart like your favorite school girl on prom night!  Good grief, sometimes I amaze myself.

It is quite obvious that all motors may be different than mine but the procedure may be the same.  The internet can provide any an all info you would probably need, especially if you read it properly!


One the leg is apart, the pump is right there.  Although I was just going to replace the impeller, once you have all of this apart you might as well replace the other items that are included in the kit.  I should point out that the main reason I was replacing my stuff was due to my negligence last year when I ran aground in the mud on Mara.  There is nothing that will shred up your impeller quicker than a dose of gravel/mud, short of you running the impeller when its dry. When I pulled my pump apart I did find gravel (photo) inside of it.  There is a stainless steel "tub" that the impeller actually rides in but, the gravel wound up on the outside of that, which is shown in that picture.  A good thing no doubt, as gravel that size could have either torn the impeller up or else clogged the cooling system somewhere along the way.

All was going well with the kit (photo) installation until I came to an area where a pressed fitting with a teflon washer was holding down a piece of the pump.  Although the book said it could be pried off of the shaft, I wound up having to cut it off with a air tool, and order new pieces.  Galleon Marine in Richmond is great for parts and service and have most everything you'd need.



I thought, or hoped, that the pressed fitting fiasco was my last problem but another one of course cropped up.  There is a Woodruff key that is inserted into the main drive shaft, which holds the impeller in place.  The kit had a replacement key so it was obvious that I would replace it.  As well, this key had to be removed to also replace a stainless steel floor plate that the impeller sits on.  This key is just pressed in however, it would appear it was glued at the factory to make installation easier.  Pound on it as much as I could, it would not come out or even loosen up.  Because that shaft goes through the aluminum casing and into the gearbox, you can't beat it up to much without causing more damage.  There is also a rubber seal directly below it so you can't apply any amount of heat to it with wrecking that.  So, what's a backyard mechanic to do?  Call on your buddies to see if they have any suggestions.  It was finally Kunckle's in Enderby that came up with the solution.  He saw the same problem in a shop he worked in and they drilled the key out!

I drilled a pilot hole right in the middle of the key first, and then drilled a bigger hole, which was the same width of the key.  I used a micrometer to measure the depth of the key so I wouldn't drill to deep.  Once the hole was complete, all it took was a little tap with a punch on one side of the key and it popped right out.  Judging by some goo on the key, it was indeed glued in!!  With the key out that plate was replaced and it did show some wear on it, possibly from dirt and/or gravel.


With no further malfunctions encountered, the installation of the remainder of the parts and pieces went together without a hitch.  Although I anticipated a problem with mating the two halves of the leg back together, it turned out to be the easiest and in fact I did it the first time!  Some motors you have to disconnect the shifting arm (especially on kickers) but on the bigger motors there is a splined shaft that has to be mated up.  Obviously my shaft wanted to be mated because it fit in most naturally! On a precautionary note and something that was also noted in the manual, make sure you put some marine grease onto the impeller, the stainless "tub" walls and on that bottom stainless plate.  When you first start the motor up there will not be any water in the pump to lubricate it and damage can occur in less than 30 seconds!

I put the leg back together and hooked up my "ears" to it.  I let the water run until it pee'd out of the top holes in the leg.  This ensures that there is sufficient water in the leg to prime the water pump.  Once this was done I fired the motor up and it did take a good minute before the water came out of the discharge hole.  This is likely because there was absolutely no water in the system after I dismantled it and hence lubricating the impeller and parts when assembling them.  There'd be nothing worse than ruining the impeller on your first start!

As you can see from the picture to the left, the used impeller blades have a slight bend to them.  I measured them and the new ones and there was no discernable difference as far as wear.  The one on the left had small crease's on the insides of the blade where it bends, but that is normal.  I spoke to Knuckles who has replaced the impeller on his inboard Merc (procedure the same) and he also said that his did not need replacement but he did anyways.  He had less than 300 hours on his motor at that time.  I should make mention, seeing as we`re talking about rubber here.  I went to our local NAPA dealer and enquired about an aftermarket impeller.  They recommended to stay with the OEM impeller, as the rubber used is the best quality you can get.  When you consider what it would cost to replace an entire motor, I`m guessing he`s right.  The complete kit cost $170 at the Yammy dealer while just the impeller runs around the $60 mark, your call on that one.  If you do decide to take on this task and need any other info plse feel free to email me and I will do what I can.  I think it is something that most backyard guys can do, even with the odd problem cropping up here and there.