Yamaha and Mariner 2hp engines have a unique way of accessing the water pump impeller, the water pump sits above the the gearbox but impeller removal requires getting inside the gearbox.

This will show you how to remove, inspect and refit the water pump impeller.

This is how I would do it, if you have a service manual follow that.

Both Yamaha and Mariner water pump repair kits are available on ebay at a reasonable price, if this is the first time you have accessed your impeller for a while it’s likely you will need an impeller, wear plate,  plastic cup and metal cup so it’s cost effective to buy a complete repair kit.

SSI Marine outboards Yamaha /Mariner water pump repair kit

Then before you start to disassemble,

1. Make your engine safe by pulling the spark plug cap
2. Remove the propeller by pulling the split pin out, slide the propeller off the shaft and make sure you retain the shear pin.
3. Drain the gear oil
4. “How to – Gearbox pressure test”

If it’s fine you won’t need to do as much but if it leaks, this is definitely the opportunity to fix it or if you don’t have the right skill set, chuck it straight into someone who can fix the leak and replace the water pump impeller for you at the same time.

5. Remove the lower unit by removing the 2 bolts which fix it to the leg (1 facing up, 1 facing down), withdraw the lower unit assembly from the leg and place it on your workbench, you may have to gently lever the lower unit off as you are separating the square section drive out the engine, the tube seal the drive shaft sits in and the water transfer pipe for the seal on the water pump housing. Do not apply force enough to damage anything, if you can’t remove the lower unit with moderate tapping, pulling and levering, pop the engine into someone who can remove it for you.
6. Next you have to get access into the gearbox by removing the cap.

Heat the split line with a heat gun (Not direct flame), I use a Black and Decker 2000w heat gun.There are slots there to allow you to prise the cap up using 2 screwdrivers but I wouldn’t recommend using this method as you stand a reasonable chance of damaging the castings.

Instead, using an aluminium drift, gently tap the cap to make it rotate slightly.

When slackened simply keep rotating and drawing upwards until it is removed

7. With access to the gearbox now you need to remove the “E” clip that is retaining the lower drive bevel gear.

The E clip is sprung loaded so use a right angled pick to pull it off the end of the driveshaft, make sure you don’t lose the clip and don’t scratch the gear or casing

The clip

 

8. Next we need to move up to the water pump housing itself.

Remove the 2 x bolts that retain the water pump housing

The apply a little heat again and gently lever the housing upwards, it will not rotate (locating pins) so don’t try to rotate it you just want to shift it so there is a small gap.

9. Lay the lower unit horizontal on your workbench.
10. Looking inside the gearbox, just behind the E clip you have already removed there is a gear which has a set of   washers and shims behind it, this will differ between different models of engine but it is essential that when we remove the gear that these are retained in the order that they were removed so that they can be put back exactly the same way.

With the lower unit horizontal, take a hold of the driveshaft above the water pump housing, look into the gearbox where you removed the clip.

 

Pull the driveshaft away from the gearbox gently and you will see it starts to come out of the gear.

Exercise caution, when the driveshaft comes out about 2 cm the gear and the shims/lock-washer will be loose in the gearbox and you need to see what order they come apart.

As you continue to pull the driveshaft out, retain the shim, washer and gear, it’s a good idea to attach them together with a piece of string or something so you can see what order the came out (and need to go back in).

This is an example of what you are removing

Continue to withdraw the driveshaft until it’s fully removed

Make sure you don’t lose the impeller drive pin

And you are left with this, finally, you have access to your impeller

However you want to do it, photo, Sharpie etc, make a note of the direction of rotation that the impeller is fitted.

1. You need to refit in the same direction
2. Never turn the driveshaft in the opposite direction when the impeller is fitted

Remove the Impeller with long nosed pliers. Gently warm the casing with a heat gun and remove the impeller metal cup and the plastic housing cup

11. The inspection of the impeller and all the other bits and pieces is no different than any other outboard

Re-assembly

Re-assembly is pretty much the reverse of the removal but there are a few points to note

When you are fitting the plastic cup and impeller metal cup into the gearbox casing you need to align first of all the tang on the underside of the impeller metal cup with the slot in the plastic cup and then the plastic cup needs to align with the recess in the casing which receives the impeller tang, this will ensure that the holes which allow the water flow in the plastic and metal cups align with the holes in the gearbox casting which let the water flow in.

Also there are alignment cutouts in the plastic cup that you need to line up before you fit the cup.

If you do all of that then your alignment is good, the plastic cup is a little fragile so do be careful with that.

When you are fitting the driveshaft back into the gear within the gearbox take some care, it’s a fiddly job to align the driveshaft splines with the gear splines, just make sure that when rotating the driveshaft to align the splines that the driveshaft rotates in the correct direction.

Post Re-assembly

Carry out another gearbox pressure test, this will ensure that everything has gone back together properly

“How-to – Gearbox pressure test”

Dunk your engine into fresh water, allow a minute or so for the pump to fill up then start the engine and make sure you have a good flow of water.

If you regularly inspect the water pump on your Yamaha or Mariner 2hp engine, the whole system will remain well lubricated including the driveshaft upper splines so it will always be easy to disassemble and re-assemble.