1974 Mercury model 650 water from cylinder?

[lunawhaler]

I just bought this motor on Saturday. When I got the boat I noticed that it was cooling properly, no water from pee hole. I investigated the impeller and found that it was not installed correctly. I purchased a new water pump housing (total kit) and replaced it. I also noticed that there were no washers on the spline of the drive shaft...which I have not replaced yet. Nonetheless, I hooked the motor up to the water and fired her up. The engine appeared to be cooling good now with a steady stream of water from the pee hole.

The problem is that I also noticed water coming from the first (top) cylinder spark plug!

Any recommendations on fixing this problem or troubleshooting it?

Thanks,
Tim

 

[chris.olson]

Re: 1974 Mercury model 650 water from cylinder?

The problem is that I also noticed water coming from the first (top) cylinder spark plug!​

Any recommendations on fixing this problem or troubleshooting it?​

It depends on whether the water is coming from around the base of the plug or out of the cylinder. I assume it's coming from around the base of the plug, which means the water jacket cover gasket is leaking. It's easy to install a gasket, but be VERY careful when removing the bolts because they twist off easily.
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Chris​

 

[lunawhaler]

Re: 1974 Mercury model 650 water from cylinder?

Thanks Chris,

That is exactly it. It's only leaking around the water jacket both side and front. Successfully removed both, but probably need new covers and definitely new gaskets and maybe bolts as well. I was happy to see the water not coming from the cylinder! Now I just need to source these old parts.

Tim

 

[chris.olson]

Re: 1974 Mercury model 650 water from cylinder?

That is exactly it. It's only leaking around the water jacket both side and front. Successfully removed both, but probably need new covers and definitely new gaskets and maybe bolts as well. I was happy to see the water not coming from the cylinder! Now I just need to source these old parts.

I assume by side and front, you mean the head water jacket cover and exhaust cover/baffle. You shouldn't need new covers. If they're not flat they can be lapped on a flat workbench with a piece of emery cloth. All you should need is gaskets and you can get those at any Mercury dealer.

I always re-install with new stainless steel bolts. You don't even want to know what Mercury Marine gets for stainless bolts and you can get them from a hardware supplier like Fastenal for a portion of Mercury's price. I also apply anti-seize compound to the threads and bolt shanks and clean the threaded holes in the engine block with a tap to make sure they torque properly (critical to keeping your covers flat and not warping, and preventing future leaks). I don't recall the torque specs offhand, but they're in the service manual.
--
Chris​

 

[lunawhaler]

Re: 1974 Mercury model 650 water from cylinder?

Thanks Again Chris,
Yes you read me correctly the water jacket cover and exhaust cover/assy. I'll check with my local dealer on the gaskets. The exhaust cover/assy has an issue with one of the bolt holes, but may not be an issue. Thanks for the insight on the nuts and bolts as well, great point!

Tim

 

[chris.olson]

Re: 1974 Mercury model 650 water from cylinder?

The exhaust cover/assy has an issue with one of the bolt holes, but may not be an issue.

Well, that could mean you have a cracked cover, a cover that's badly erroded around one of the bolt holes, or possibly a bolt hole in the engine block that either pulled the threads out or is loose.

The covers can be fixed with JB Weld. The stuff can be filed, sanded, machined or drilled after it cures, and it is every bit as durable as aluminum. I've fixed everything from exhaust covers to cylinder heads to crankcases on older outboards with the stuff, and it works.

If you have a bad bolt hole in the engine block, you can drill it oversize, tap the hole, coat a helicoil thread repair insert with Locktite, and screw it in to repair the threads.

Hope this helps. You don't even want to know the price of those covers, new, from Mercury Marine. They are VERY expensive. If you need a replacement cover and can't find one used, I'd explore every avenue to repair the old one first.
--
Chris​

 

[redjmp]

Re: 1974 Mercury model 650 water from cylinder?

Never mind the gasket or lapping the plate.
If you look carefully around the plug that leaks, I bet you will find some pitting in the metal on the block around the plug.
Just clean both surfaces well and get all the corrosion off and then use rtv blue and no gasket.
Its quick and easy and it works!