Lower Unit Removal - 1973 650

davidsain

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Aug 1, 2015
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I'm new to boating. Dad gave me his old '72 Fiberfoam 16' Columbiana with a '73 Mercury 650. The water pump doesn't work, so I want to remove the lower unit and rebuild it. There are 3 5/8" nuts, but that's not enough to drop it. I thinkI need to remove the trim tab. There is a hole above to access the nut for the trim tab, however I can't fit anything larger than a 3/8" drive 1/2" socket in there, but it's not big enough for the nut. I suppose I need to purchase a thin wall socket, but don't know what size the nut is. Any ideas?
 
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davidsain

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Aug 1, 2015
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I was trying to remove the lower unit in the evening. Now, in the daylight I was able to see that it was a 12 point bolt. I used a 12 point 7/16 socket to take off the trim tab and found a 9/16 nut underneath. The lower unit slid right off. No wood wedges or anything.

Once inside, I found a mess of rubber inside the water pump housing. Nothing left of the impeller blades. Inside of the housing has some rough crud stuck onto the top. So I'll order an entire water pump kit.

As the impeller exploded, I imagine some of the smaller bits could have made their way up the water pipe and into the cooling jacket, potentially plugging the outlet tube. I've ordered an old Mercury factory service manual and expect to find what I need in there, but any insight would be helpful.


I'm looking at http://www.sterndrive.info/mercury-o..._drawings.html to identify parts.

Below part 16 referenced in the above link, the Exhaust Leg Seal Plate (correct name?) was in pieces when I went looking around. not all of the pieces are there, so I imagine they've been gone for a while. It looks like http://www.egmcartech.com/store/Merc...651095839.html, but I haven't been able to identify that this is the correct part. Any pointers to this part would be helpful.

Edit: I found something that looks like the same, but don't know if it covers my model. It's a pn 92815 Plate, Exhaust Seal. There are a number of places (Amazon, eBay, Crowley Marine) that carry this for $10 or a little more. http://www.crowleymarine.com/mercury...rts/465_18.cfm lists this part (#9) for a 1975.



The Reverse Lock Cam is made of plastic. The ramp surface is pretty rough and there are worn spots for neutral and reverse. Is this normal and should I be concerned?

I read about how Roberta rebuilt her lower unit at https://www.glen-l.com/phpBB2/viewtopic.php?t=13928 and her's appears to be aluminum. This page http://www.nlamarine.com/products/me...ant=1110590244 mentions that both plastic and metal were made. Are they universal? Looking at 43308-1 (plastic) or 43308T-1 (aluminum) (both on eBay)

Thanks for your time

David
 
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davidsain

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Aug 1, 2015
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I've managed to figure this out. Some trial and error. The '75 plate was a match for the '73. Water pump base I ordered based on a part number from Crowleys for this Serial Number didn't fit. There is a notch on the bottom for oil to drain back to the gearbox. Different place. The flush hole isn't drilled out and the base is 3mm larger in diameter. However I was able to use the old base and the rest fit together just fine.

Had some issue with the reverse cam alignment and shifting, but once I realized I just put into forward (so the pin hits the bottom of the ramp) and the shifter into forward, all aligned perfectly.

Now I've got it running and water spraying out of #1 cylinder. Pulled the water jacket cover and there are some cracks and a hole in the #1 cylinder. New block or throw the entire thing away. New thread.
 

mlbinseattle

Petty Officer 2nd Class
Joined
Aug 1, 2015
Messages
100
Sorry to hear about that especially after all you put into it. You might try looking for a rebuilt powerhead. Probably will be a few bucks, but should be worth the money considering what entire engines cost these days.
 
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