1968 mercury 650 65 hp/cooling issues

kld10678

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Mar 27, 2010
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Hi, new user here. I just bought a boat with a 1968 mercury 650 65 hp ss outboard. It started right up but no water was coming out of the exhaust ports or the pee hole just a little exhaust smoke. I ran it for a few seconds a few times. I used a pipe cleaner to check the pee hole and i dont think it is clogged but im not positive. the motor did sit for a while not sure how long but probably at least 3 years. I know that it is probably the water pump impeller. Considering that I have done some lower unit repairs on a 69 johnson 33 hp, how hard is this repair and around how much should i expect to pay if I have a shop do the repairs. any help with this would be greatly appreciated. thanks
 

emckelvy

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Jan 16, 2004
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Re: 1968 mercury 650 65 hp/cooling issues

It isn't that hard of a job, and easier than the Johnrude in that there's no shift linkage connector to undo.

Instead, Merc uses a female-splined coupler at the lower end of the upper shift rod. This engages the male-splined end of the shift shaft in the lower unit. Rotary motion rather than up-and-down motion is used to shift gears.

So, when you pull the lower unit down, the shift shaft just "falls" out of the coupler.

The one caveat is, when the lower unit's off for service you don't want to move that shift shaft. And it's best to have shifted the control box to Neutral before you remove the L/U, and leave it there.

Most common error is to move the shift shaft, then when you put it all back together it won't shift out of Fwd gear. Since there are no flats on the shaft or coupler, they can be reassembled in any position. This won't happen if you leave things as is.

Aside from that, the only 'trick' thing is a hidden bolt under the trim tab. This is accessed from the top and could either be an allen socket bolt, 12-point head or hex. Merc used varied styles over the years. Pop the plastic plug (if it's still there) covering the hole and check out with a strong lite. If there's some rust/crud in there, dig it out and you'll likely find an allen socket.

One nut in the front, one on either side, two nuts underneath, and one bolt you'll see after the trim tab is removed.

Reassembly is very straightforward, use some waterproof grease on all the studs/bolts, also grease the end of the aluminum exhaust tube where it engages the rubber exhaust seal in the gearcase. There is a plastic 'guide tube' that sticks up out of the pump housing and helps 'catch' the water tube on the way up. Sometimes the guide tube works its way out of the pump and stays on the copper water supply tube; just pull it down and reinsert into the pump. Most pump repair kits will have a replacment anyway. A bit of grease on the end of the water tube will ease its way into the rubber pump grommet.

You can pick up parts here at the iBoats store, a few places where you'll find parts diagrams are www.boats.net www.crowleymarine.com or http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

BTW if the local repair folks want to charge you much more than an hour or so for an 'easy' impeller replacement, think twice. Unless your motor is an Old Salty Dog it should come apart and go back together with little effort. If the gearcase has other issues while it's off (such as leaky seals etc), of course more time would be involved.

HTH............ed

p.s. do a compression check before you pour a lot of $$$ into it. Hopefully the impeller is worn from years of inactivity, but it also could be an indicator of a badly overheated/damaged powerhead.

p.s.s. if you keep this motor and want to properly maintain it, get a good service manual! ;)
 

kld10678

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Mar 27, 2010
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Re: 1968 mercury 650 65 hp/cooling issues

Thanks for the info. i think i will tackle this myself. I do plan on getting the manual for it. I just got this boat a few days ago and got such a good deal I dont mind putting some money in it. Thanks again
 

kld10678

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Mar 27, 2010
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Re: 1968 mercury 650 65 hp/cooling issues

Why does it say in the manual to put it in forward gear. You said to keep it in neutral but i cant tilt the motor unless its in forward gear. i havent done anything yet
 

emckelvy

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Jan 16, 2004
Messages
2,506
Re: 1968 mercury 650 65 hp/cooling issues

While it's true that the motor locks down in Neutral, what you can do is put it in Fwd, tilt up the motor, then shift back to Neutral.

The reason it's generally recommended on this forum to leave it in Neutral when you drop the lower unit, is that there is a positive detent in Neutral. The shift shaft will tend to stay in that position. Whereas if you shift to Fwd, the shift shaft can easily be rotated away from the proper position because there's about 270 degrees of free play in the clockwise direction with the gearbox in Fwd. If you were to accidentally turn the shaft while you were working on it and didn't realize it, when you reinstall the lower unit it won't shift out of Fwd.

If you're very careful to note the shift shaft position when you pull the L/U, you can leave it in Fwd. Otherwise it'd be better to leave it in Neutral. When you reinstall the L/U, rotate the flywheel a bit clockwise to engage the driveshaft. Pull the plug wires first to remove all possibility of an accidental start.

If you should find the shift shaft out of position, for Fwd gear you would gently turn it CCW until you feel some resistance. From that point on you'd need pliers to turn the shaft (cushion plier jaws with tape if you do this). One 'click' CCW from the correct Fwd position of the shift shaft and you'll find Neutral.

If you have a lot of trouble getting things lined up in Fwd, shift the L/U to Neutral, also the control box and try again.

BTW when you're done, shift the control box to Fwd and then you can lower the motor. Never lower the motor when it's in Neutral or Reverse, as the reverse lockout hooks will bind on the tilt pin. Mercury intentionally designed it this way, otherwise if you were to chop the throttle (or the motor should quit) while underway, and it wasn't locked down, the drag at speed would cause the motor to kick up sharply and damage motor, transom, or both.

HTH.........ed
 

iliketrout

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Apr 7, 2010
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Re: 1968 mercury 650 65 hp/cooling issues

emckelvy,

Does this procedure work on a 1976 9.8HP?
 

kld10678

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Mar 27, 2010
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Re: 1968 mercury 650 65 hp/cooling issues

iliketrout, you may have to start a new post he may not come back to see your question. My manual doesnt cover that 9.8 hp so im not sure how much different it is from mine, I was able to leave mine in forward when I dropped and reinstalled the lower unit. You definitly want to get a manual if your replacing the water pump impeller or any other repairs. Good luck
 

iliketrout

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Apr 7, 2010
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Re: 1968 mercury 650 65 hp/cooling issues

Thanks kld. I purchased the Seloc manual as I didn't find anywhere to buy the original dealer service manual. Over 3 weeks and still waiting from Amazon!
 

kld10678

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Mar 27, 2010
Messages
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Re: 1968 mercury 650 65 hp/cooling issues

If you would have bought it here on iboats you would have gotten instant online access for your book while you waited for the manual. Thats what I did and the hard copy only took 4 days to arrive. Oh well probably too late now unless you can cancel your order
 
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