Im in the middle of fixin up a bass boat we just bought and the last thing to do to the motor is replace the impeller. I took the lower unit off and when I pulled the casing off to get to the impeller, the impeller stayed on the shaft and I can't budge it. I noticed on all the tutorials, the impeller came out with the top of the housing? The motor is an '87 135 mariner. The impeller is absolutely shot, but I cant seem to get it off the shaft and was wondering why it didn't come off with the housing? Any thoughts?

Probably been on the shaft way to long.

After you remove the cover from the drive shaft the impeller should slide off. On occasion I have had to split the impeller with a hammer and a chisel if you are unable to drive it off the shaft with a hammer and a punch. Be sure to remove the key from the shaft.

Remove the face plate and seperate it and throw the inner gasket away. It will need to be replaced. If it is so equiped remove the flush plug and gasket from the gear housing. DO NOT replace the impeller only if it is in this bad of shape. Go ahead and install the complete assembly.

I'm thinkin Im am going to have to split it. What happened was, our boat mechanic replaced the tilt trim unit and just to check, he started it up (we have not had it on the water) and he tested the water pump and it did not work. He gave us the impeller and told us to replace it. He did not give us the kit though? He said it should do it. Although, I will say, the impeller on there now is in HORRIBLE shape. The edges are torn off and it just looks horrible.

Where is the key located? Also, if I do split it, what did you use to get through the metal liner on the inside? I'm not sure what it is made out of, our how soft it is. Will it give a little if the rubber is cut off?

I just changed three impellers on some of my motors.  None were stuck to the shaft.  

The impeller did not come off with the housing because the center of it is fused to the shaft.  

You need to determine if the center of the impeller is metal or plastic. If it is plastic you can just hacksaw it just about through and finish by tapping in the cut with a chisel.  If it is metal then you can still hacksaw it and crack it the same way. Be VERY careful splitting it. You do not want to be pounding on the drive shaft if it is not supported or on the surface of the lower unit around the impeller.  There will be a key on the shaft that drives the impeller. Don't let that get lost. Check the inner surfaces on the impeller/water pump housing.  If it is all scratched up you either need to sand with fine sandpaper until if is smooth or replace. If the inner surface is rough, it will immediately chew up your new impeller.

If you take the rubber off, it will not loosen up any. The part of the impeller that is stuck to the shaft does not have any rubber on it.

If you are not sure about this, take the lower unit back to your mechanic and let him do it. Better to spend a little than a whole lot.

Did you drain the gear  lube from the lower unit?  Just as important as the impeller. If the lube is a creamy light color then you have water leaking into the lube and you will need to replace the seals around the drive shaft upper and lower.  Also replace the seals on the drain/vent screws.  You refill the lube from the bottom up. Don't just stick the nozzel of the refil bottle in the top vent hole.  Air pockets will form and you will not get the right amount to the gears.  

You say the impeller was in bad shape and your mechanic says it was not pumping....who had the boat before you and do you know if the motor has overheated. If so, there might be head gasket damage. Do a compression test. Just because the motor runs does not mean it might not need further testing.

I'm thinkin Im am going to have to split it. What happened was, our boat mechanic replaced the tilt trim unit and just to check, he started it up (we have not had it on the water) and he tested the water pump and it did not work. He gave us the impeller and told us to replace it. He did not give us the kit though? He said it should do it. Although, I will say, the impeller on there now is in HORRIBLE shape. The edges are torn off and it just looks horrible.

Where is the key located? Also, if I do split it, what did you use to get through the metal liner on the inside? I'm not sure what it is made out of, our how soft it is. Will it give a little if the rubber is cut off?

Again, do not just replace the impeller. You need to replace the entire assembly. It is obvious that the water pump has lacked the attention needed in the past. I normally change the impeller every year and the entire assembly every other year.

Just as the above post stated, do a compression check as this motor could very well have been overheated if it was run with the pump assembly in this kind of shape.

Better to catch it now than doing even more damage by running it without the check. While your at it check the poppet valve located on the starboard side of the motor. You can take it off and disassemble it, clean it, and reinstall. It is located down low and is about the size of a silver dollar. It has an internal diaphram that has a screw in the center holding it together.

Thanks for the help guys. And the compression has already been checked along with everything else. Everything checks out perfect except that dang water pump. I'm goin to try to get this thing off, and then go from there. THanks again.

Before you go beating on it just carry it to the shop and have them remove it for you. You can do more damage than you care to pay for if you are not careful.