Mercury 7.5 water pump melt-down . . .

[tpenfield]

Last year the water pump on my 1969 Merc 7-1/2 hp crapped out (S/N 26346XX). No big deal, I figured, I'll get a new impeller. I took the lower unit off yesterday and went about disassembling the water pump.

the thing looked more like a melt-down than just a simple failure of the impeller. It seemed that the impeller and the pump housing had melted a bit.

I have new parts on order for the pump, BUT . . . .

In the process of getting the old impeller out, it seems that the bronze/brass hub of the impeller has become 'fused' with the drive shaft.

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I cannot seem to get the 'hub' (which look like a hex nut in the picture) to slide up off of the drive shaft like it is supposed to. FWIW - this driveshaft is not original to the motor - it is a stainless steel shaft from a 1980 version of the Merc 7.5

Just wondering if anyone has any ideas, tips, tricks to get the hub off. :noidea: I can see the 'pin' that acts like a key to turn the impeller with the shaft, but the hub itself seems to be one with the shaft . . . probably because of the apparent amount of heat during the 'melt-down' :noidea:

TIA for any thoughts on this. I don't want to try to cut it, fearing that I may cut into the driveshaft a wee bit.

I've been using the Johnson 4.5 in the meantime, but to add insult to injury, the Johnson decided to crap out yesterday Me thinks it is a fuel flow problem, but that is a story for another time.

 

[Scott Danforth]

use a dremel to split the brass hub

 

[tpenfield]

Quick update . . .

I can't seem to find my dremel tool . . . so maybe I'll just be careful and use a small file to cut into the hub and then split it before I cut all the way through.

Still waiting on the water pump parts, but they should arrive soon. Meanwhile, I got the Johnson 4.5 hp running again. Amazing what a little bit of acetone and seafoam directly down the fuel line can do

Additionally, the Admiral's aunt mentioned that she has an old outboard motor (3 hp of unknown brand/model) that I can have. So, for the price of a courtesy dinner, I'll have 3 outboards. I believe that outboard is about 30 years old, and was only used for 1 season, back in the late 1980's. Should be interesting to see if it 'turns' and if it can be made functional (again)

I figure with 3 outboards of 50, 40, and now 30 years of age, I ought to be able to keep at least one of them running

 

[nola mike]

Looks like it would be tough to get a Dremel in there. Does that nut need to come off to remove the housing? Or might need to sacrifice that as well. Guessing there's a woodruff key there, so you can't remove it by twisting. BTW, number of small outboards doesn't matter. I keep buying them when I find a good deal, but I haven't found the time to get any working (2.2hp Merc, 2.Something gamefisher, 2 electrics, 5hp Ted Williams, 2 hp Johnson --haven't even attempted to start the latter 2

 

[tpenfield]

Yes, the hub (nut) has to come off. I'll figure something out.

Meanwhile, the parts for a new water pump arrived yesterday. Also, I picked up the motor that the Admiral's Aunt is giving us . . .

A new (unused) 1990 Yamaha 3 HP (model 3D) . . . The Uncle bought it in 1990 and never got the chance to use it. It has been sitting in their basement for 30 years !!!

 

[tpenfield]

Correction . . . I think the Yamaha is a Model 3SD :noidea:

 

[tpenfield]

The Yamaha after sitting for 30 years works !!!


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I ran it for about 2 hours tonight with a heavy dose of oil and seafoam in the fuel to clean out the carb and get some break-in done.

This will take the pressure off to fix the Mercury.

 

[nola mike]

Lmk when want to get rid of it, I'll pick it up when I visit my dad in mashpee

 

[tpenfield]

Oh what luck . . . as I was working on removing the remains of the water pump impeller, I noticed gear lube coming out from around the propeller . . .



Looks like I'll be re-doing the lower unit seals too :facepalm:

 

[tpenfield]

Quick update . . .

I have not had much time to fiddle with the Mercury 7.5 . . . Today I was able to get the impeller hub 'sliced' open with a sharp chisel and managed to get the hub and water pump housing off of the drive shaft.


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Not much left and part of the impeller was fused to the SS 'cup' of the pump. So, it is good I got all new parts.

One thing that I did not realize is that the new housing part came with the SS cup and the lower seal . . . could have save a few bucks since I bought those parts too. :facepalm:

I just have to order the prop shaft seal and the shift shaft seal, so all seals will be new.

I have to take the retaining ring/nut off the lower unit hub, and for some reason, I cannot find the special tool that I had when I replaced the seals about 5 years ago.

I might just order another one . . . often I find that easier than searching for it.

 

[garbageguy]

...I might just order another one . . . often I find that easier than searching for it.

I hate it when that happens. Interestingly, when the Admiral and I were meeting another couple of our "vintage" last night, the woman was talking to me about her hubby doing that as well - Good to know I'm not the only one.

Nice score on the older, unused, Yammy

 

[nola mike]

Quick update . . .


I might just order another one . . . often I find that easier than searching for it.

Best way to insure that you find the old one.

 

[tpenfield]

OOOPPPS . . . I did it again. Melted the impeller/pump. . . again.

As i was untying the line for the dinghy at the bow, the prop/LU of the Merc came out of the water for a few seconds . . . that was enough to kill the impeller and then the water pump did another melt down.

It seems that the impellers on these things have a low tolerance for lack of water supply . . . more so than the Yammy's I've had.

Looks like I'll be ordering another impeller & water pump parts.

 

[racerone]

Rub your hands dry and you feel the heat.-----Running one of those or any impeller dry for 10 /15 seconds just kills them.-----Found 2 impellers burned on 70 HP motors last year.----Many novice boat owners learning the facts these days !!

 

[tpenfield]

New parts are on order . . .

Note to self . . . turn off the motor if going to the bow of the dinghy

 

[tpenfield]

With a burst of motivation, I fixed (replaced) the water pump on the Mercury and got it running again. I had to run some barnacle buster through the cooling system and blow some air through it as well in order to get a decent flow of water.

I think the cooling system could use a heavier dose of barnacle buster, but that can be a Fall put-away project.

It seems like we are supposed to have a windy day on Sunday . . . something about a hurricane . I saw , a guy tending the line on his dinghy from the bow while the motor was running. I think he toasted the impeller, just like I did.

Lots of folks taking their boats out. Based on the forecasted track of the storm we will have off shore breeze and a flat ocean.