KH7 water pump

[mercuryman]

I just got a Mercury KH7 and it has the old style small water pump impeller. What can I do for a new water pump impeller ?

[billw]

I don’t know but I would sure like to see it. I have never seen one. If you at least post some dimensions of what you’ve got, maybe we can come up with something, if nobody has a direct answer to your question…..which I hope they DO!

Long live American manufacturing!

[richardg]

You need to pull the original water pump cavity out of the lower unit and then install the new longer one. The replacement water pump cover is much thinner than the original. Together these increase the volume of water pumped to help the motor run cooler. Hopefully the pistons and cylinders were not overheated badly in its former life.

It is also necessary to drill additional inlet holes in the lower unit on the opposite side as the ones originally provided.

I think these notes are covered in the service manual and parts lists.

Sometimes it is easier to find a whole new lower unit since there were other issues associated with an too small bearing on one of the gears.

[johng]

You want to look for a Mark 15 or a Mark 20 Lower Unit they are more plentiful. It is a bolt on swap for the KH-7 with all the right parts and correct water inlet holes. Same impeller fits MK 15, MK 20, MK 25, and MK 30. The early KH-7 impeller was only about 1/2" tall. the new style is almost 7/8". New impeller # is 47-20813 Mercury part. or Sierra # 18-3008 good luck.

[billw]

While it is easier and better to change the whole lower unit or water pump cartridge, you don’t want to get rid of the original, either. It is kind of historically significant, if in a bad way. It would make a great conversation piece. If you’re just going to ding the old one, I’d love to have it…..

Long live American manufacturing!

[mercuryman]

Well it looks like a special tool is required to pull water pump so a new lower unit might be in order. I will keep you in mind BillW if I get a new one.

[billw]

Even if you had the special tool, it is very doubtful that the tool would work as advertized. It might work fine on a factory fresh motor; but on one where the cartridge has been sitting in there corroding, forgedabowdit. You can disassemble the gear case and use the drive shaft to pull it out. Much more likely to succeed, that way….and you can reseal the whole thing while you’re there, because odds are very strong that it could use it….It’s a lot of work and other gear cases are available; although I would not call them plentiful. Most old Mercurys left the planet to return to Carl, BECAUSE of gear case failure, due to water intrusion. IMHO, you might just consider fixing the one you have, that is, hopefully, still intact.

Long live American manufacturing!

[20mercman]

You should be able to pull the lower unit apart by first pulling the prop shaft. Then remove the drive shaft pinion nut, have the water pump cover off of course. Then place the drive shaft in a vice and with either a dead blow hammer or protecting the housing with a block of wood, you can drive the lower unit off of the drive shaft and this will remove the water pump housing at the same time. There is no need to swap out lower units unless you want to. I have two KH-7’s and two other motors that have KH-7 lower units on them. There is nothing wrong with them. They do take a F-11K forward bearing, same as the reverse bearing in all of them. Mercury did upgrade the forward bearing, but I have never seen one that was damaged by anything other than rust. There are differences in the drive shaft, but that also is not a problem. You just need to use a short pin for the water pump drive key. Like I said, don’t fret it, it is not difficult. Also, as you lower unit is unconverted, you will most likely need to add the additional water intake holes just forward of the prop. Some folks turned their lower units into Suisse Cheese by drilling a bunch of holes. You need 12 total, 6 on each side.

Steve

[mercuryman]

Now I think I understand how to remover pump housing, is it the roller bearing that pushes the pump.

[20mercman]

quote mercuryman:

Now I think I understand how to remover pump housing, is it the roller bearing that pushes the pump.

Yes, the ball bearing under the water pump will force the pump assembly out of the housing with the drive shaft.

There is a small alignment pin on the side of the housing. Be sure to grab it as the assembly comes out. This pin keeps the assembly in proper alignment with the inlet and outlet cavities in the housing.

Steve

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