1973 Mercury 7.5 Impeller/water pump help

[Susky_65]

Hey everyone,

I'm new here and I am seeking some advice to a problem I am having in regards to my outboard. It's an older 7.5 HP motor that I was just recently able to get back running (somewhat). I noticed that it was not pumping water so I decided to change the impeller. From what I have heard about this motor, this impeller has never been changed before( !)

After taking apart the lower shaft and the pump housing, the impeller was completely shredded as you might expect from a situation like this. The problem is that I cannot even see where the woodruff key from the pump is or how to get to it. The new impeller I ordered does not seem to fit, there is a hex brass nut looking thing on the bottom of the pump shaft. I am unsure if this belongs here or if it is somehow a remnant of the old impeller. I had to piece by piece remove the old impeller due to the condition of it.

I am at the point now where I ordered a separate part number to see if it would slide over this hex shaped nut but I have my doubts since I cannot locate the key slot like I said earlier. So I guess I am seeking some advice on whether this thing is actually part of the pump housing or if it is something that needs to be removed. It is in that spot very strong and will be difficult to remove if so. I snapped some pictures for this post as well:

As you can see there is that large nut looking thing down the bottom of the shaft. Not sure if it is somehow an old part of the old impeller or if it belongs there. Wondering if the new part will fit over it (hopefully). Thanks for your time

 

[flyingscott]

That hex is the old impeller hub with no rubber on it anymore, it needs to come out.

 

[racerone]

Did you find most of the old impeller ?-------Might want to do a compression test too.------There is a plastic washer at the very top of the copper tube going to the powerhead.----This washer often melts on severe overheat and blocks water flow.

 

[Susky_65]

Thanks for the replies...yeah I think I found most of it. This is definitely what I was thinking. I will try and figure out a way to get rid of that thing then. I do have a compression tester and I'll look out for that washer as well, I did not see it at all which probably means it was melted. Unfortunately this thing wasn't well maintained

 

[tpenfield]

BTDT . . . see the link to my thread on replacing the water pump on my 1969 Merc 7.5 . . .

https://forums.iboats.com/forum/eng...rds/10778198-mercury-7-5-water-pump-melt-down

As stated the hex is the hub of the impeller. It is probably corroded to the drive shaft, so you will need to take a file and carefully cut it off. You probably will need a new key for the shaft.

Is the rest of the pump body OK. Wonder where the fragments of the impeller went :noidea:

Inserting the impeller into the cup is a bit tricky . . . As you are looking down on the impeller, it spins clock-wise.

 

[Susky_65]

Hey, I read through your thread. Haha that is really something, that's exactly like mine! I'm glad you were able to get yours off. It is crazy what some heating can do to the engine I guess.

I managed to get the hub off today, I struck it with a chisel and hammer for awhile and didn't have a ton of luck, so eventually I took a risk and used a small drill bit and finally cut through the hub very slowly. Took about 3 hours total but managed to save the woodruff key as well. I put the new impeller on and as you said, lining it up with the key is definitely not anything I want to do for awhile again. I need to put new gear lube in the lower shaft before testing it out, but first I need to get the lower shaft back on which is a challenge. Any tips there? Thanks a lot guys

 

[tpenfield]

Do you mean 'get the lower unit back on' ?

I think the shift shaft does not like to line up and it prevents the LU from going back on. The LU will stop about 1/4" short of mating with the exhaust housing. If I recall, you got to fiddle with the shifter slightly to get the shift shaft splines to line up. Make sure you have proper shifting before you secure the bolts.

 

[Susky_65]

Yeah that was what I meant, thanks a lot for the help. I'll keep working on it. It definitely doesn't like to line up

 

[racerone]

You just need to keep the 2 parts lined up.-----Done many of them and it takes just seconds to assemble these units.